THE MAGAZINE FOR CONSUMER ELECIRONICS SERVICING ... · ELEGT111311THE MAGAZINE FOR CONSUMER ELECIRONICS SERVICING PROFESSIONALS .0 Se c (-g & Te C rrology JULY 1989/$2 5C Servicing

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Servicing Zenith Microcomputers • Scan-Rectified Voltage Sources

Implementing an Electrostatic Discharge Awareness Program

Setting up an electronics

servicing workbench

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Contents Volume 9, No. 7 July 1989

r

11:11E-M1111 MIME CD NOCE CLI 113

Page 6

FEATURES 6

12

Setting up an Electronics Servicing Workbench By Conrad Persson If you're still using the same old tools you've been using for years, you probably don't even realize how much nicer the job would be with the right tools, kept in top shape. Whether you're setting up your first bench or improving your old one, here are some ideas for setting up a top-notch shop.

Servicing Scan-Rectified Voltage Sources By Homer L. Davidson One plus of scan-rectified B+ voltages in TV design is the elimination of unwanted heat from B+ dropping resistors. One minus is they are guaranteed to stop producing voltages when the horizontal deflection ceases, and when you add start-up and shut-down functions, the problem can be a bit intimidating.

38 Servicing Zenith Microcomputers Part I: The Backplane By John A. Ross This article begins a series on servicing Zenith microcomputers. In Part I, the author introduces the

g it ac e t iNi o gvi gn ia g

&

Page 12 Page 50

44

series with a detailed look at Zenith's backplane design, which interconnects all the circuitry contained on modular printed circuit boards. A close look at the backplane gives the servicer an understanding of how the circuitry works — a big help when you have to figure out why it doesn't work.

Implementing an Electrostatic Discharge Awareness Program If you want to make the world a safer place for those poor little static-sensitive devices, take a page from the program developed by the Airborne Electronics Division at Robins Air Force Base. You might not need to be as detailed as the Air Force — they even specify the floor wax — but you'll get an idea of how big the ESD problem is for performance-critical components.

DEPARTMENTS 2 Editorial Managing Information Overload

4 News

10 Troubleshooting Tips

20 What Do You Know About Electronics? Voltage Phasors

22 Feedback

24 Test Your Electronics Knowledge

27

46

Profax

Products

48 Symcure

49 Books

50 Business Corner Setting a Fair Price

51 Literature

52 Audio Corner Troubleshooting Problems in the De-emphasis Circuit — Part I

54 Computer Corner IBM Personal Computer Servicing Do's and Don'ts

56 Video Corner Using Logic in Troubleshooting — Part I

58 Readers' Exchange

60 Advertisers' Index

ON THE COVER Setting up an electronics servicing workbench requires the right tools and clean-ing products, plus some extras the servicer might not think about, such as proper lighting and ventilation. Even if it doesn't save time, a well-planned workbench can make any job easier and more enjoyable. Photo courtesy of Contact East, a supplier of electronic products.

July 1989 Electronic Servicing & Technology 1

Editorial

Managing

information

overload

Not too long ago, I saw a show on PBS that dealt with the problems of being a pilot in the new generation of fighter air-craft. It dealt with such things as the sheer physical challenge of remaining conscious through a multi-G turn, out-maneuvering crafty enemy pilots, and many other concerns facing today's fighter pilots. One of the most fascinating — and

chilling — segments dealt with the con-sequences of information overload. One Vietnam War U.S. Air Force pilot with whom the show's producers talked had been shot down; he had failed to take evasive action even though his wingman had shouted at him repeatedly that there was an enemy fighter on his tail. The pilot's eyes and ears were bom-

barded with information. He was watch-ing the terrain below glide past his air-craft; in the air he watched many aircraft, both friendly and unfriendly; and he had to monitor his radar and his instruments. His earphones crackled with radio transmissions — the air controller was issuing information and instructions for all friendly aircraft in the vicinity, the surrounding aircraft were com-municating to coordinate the battle. The pilot's mind was like a computer, racing to process all of this input and react to it. When the critical warning came, all of his faculties were stretched to the limit, and it didn't get through. The con-sequence was that the enemy had a sit-ting duck for a target and the plane was shot down. Sometimes I think that in today's com-

plex and fast-moving world, we're all a little like that pilot. We're constantly assailed by information that's important to our lives, so much so there's a serious danger we'll miss a critical piece of in-formation. That's especially true in oc-cupations where the pace of technological change is so fast it's almost impossible to assimilate it all, as in the case of consumer electronics servicing technicians. Think about all of the technology

developed for consumer use in the past few years: compact discs, personal com-puters, cellular telephones, facsimile, satellite TV, stereo TV, surface-mount components, Walkman-type products. Now there's news of high-definition TV, fiber optics and more. Is something out there shouting a warning we can't hear because of the other noise?

I don't know, but here are a few thoughts about keeping the noise at a manageable level: • Try to separate the interesting from the truly critical. For example, there's been a lot of talk about HDTV. It will be here one day, and technicians will have to deal with it. But a standard has yet to be developed, so it will be years before anyone is called on to service an H MV set. Keep an eye on this kind of technol-ogy, but don't let it distract you from what's here now or just around the corner. • Once you have sorted out what's im-portant, sort that information into what's important to you and what's important to someone else. In other words, com-puters, facsimile and cellular telephones are all facts of life today, and every technician should be aware of them. However, if you plan to concentrate on servicing computers, you might want to put learning about the intricacies of fac-simile machines on the back burner. • Concentrate on the technologies that affect several areas of electronics. For ex-ample, some readers might pass right over articles about ESD, but with microminiaturization as the wave of the future, ESD is real and here to stay. On the other hand, if you see an article about a technology that really doesn't interest you or affect your area of expertise, target another article. • Don't force yourself to remember everything. Keep up your files, and if the files themselves become overwhelming, consider investing in a computer that can manage the unmanageable stack of infor-mation. And don't rely on memory to the detriment of good, basic troubleshooting skills. Remembering that diode xyz is a troublemaker in model abc TV is only helpful if it is a common problem in a common model. If you try to file away every case history on the off chance you might see that particular symptom again, you're sure to frazzle some brain circuits. • Try to keep an open mind. One way not to deal with information overload is to refuse to accept any new information. If you only want to service TVs and someone brings in a VCR, stop and think about it. You won't know whether it's a potential gold mine until you at least look at the technology.

2 Electronic Servicing & Technology July 1989

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News Survey rates service quality

Americans rate the repair service they receive higher than some recent publici-ty would suggest, according to studies by W.J. Lynott, Associates, a Glenside, PA, consulting company. Using what they call Customer Satisfaction Audits, the company surveys recent service customers of client companies to learn their attitudes in five key areas of customer satisfaction: quality of workmanship, promptness and depend-ability of the service, courtesy of the service personnel, the price charged and overall satisfaction. The replies are converted to numeric

scores in each of the five areas. A na-tional average of all respondents is maintained so client companies may compare their scores with the average of their competition. The current na-tional averages are (on a scale of 1 to 10): quality of workmanship, 8.33; promptness and dependability of the service, 9.28; courtesy, 9.33; price charged, 6.83; overall satisfaction, 8.03. For a brochure with further informa-

tion, write W.J. Lynott, Associates, 614 N. Easton Road., Suite 200, Glenside, PA 19038, or call 215-886-3646.

Report analyzes future trends Revenues from integrated optical and

optoelectronic circuits will increase from $662 million to $1.06 billion from 1988 to 1994, according to a report published by Frost & Sullivan. "The U.S. Optoelectronics and Integrated Op-tics Component Market" (#A2087) analyzes optoelectronic technologies, the products and expanding product markets, industry trends and competitive strategies. Product markets examined in the study range from light- and infrared-emitting diodes, which have reached commercial maturity, to the still emerg-ing growth areas of integrated optical and optoelectronic circuits. According to the study, by 1994 or

earlier, the market for integrated optical and optoelectronic circuits will be ready for a rapid upturn. Although the present U.S. market for optical ICs (OICs) is still small — $8 million in 1988 — that market is expected to increase to $56 million by 1994. Other trends forecast in the report include the following: • The optocoupler market should grow from $120 million in 1988 to $190 million by 1994.

• The largest optoelectronic market. LEDs and IREDs, will grow from $224 million in 1988 to $353 million in 1994. • LED display revenue will increase from $134 million to $169 million be-tween 1988 to 1994. • Diode lasers, a $54 million market in 1988, will be a $90 million market in 1994. • The photodetector market will in-crease from $68 million to $112 million from 1988 to 1994. • The photovoltaic market will expand from $54 million in 1988 to $88 million in 1994. For more information on the report,

contact Customer Service, Frost & Sullivan, 106 Fulton St., New York, NY 10038; 212-233-1080.

NPEC publishes seminar schedule The national Professional Electronics

Convention seminar schedule will in-clude sessions on VCR servicing, digital and microprocessor technology, oscilloscopes and more. The convention is scheduled for August 7-12 at the Loews Ventana Canyon Resort in Tuc-son, AZ. The seminar schedule includes the following sessions: • Troubleshooting VCR system-control servos, presented by Sharp, August 7 • Basic digital, a 2-day school presented by the Electronic Industries Association (EIA), August 8-9. • Advanced microprocessor, a 2-day school presented by the EIA, August 11-12. • Servicing Super VHS, presented by JVC, August 8. • LaserVision videodisc technology. presented by Pioneer, August 8. • Technical operation of the CEBti. presented by the EIA, August 11. • Troubleshooting microwaves to the control-panel level, presented by Sharp. August 11. • Camcorder servicing, presented by Hitachi, August 12. • A scope school, featuring advanced techniques for waveform analysis in servicing high-tech consumer products, presented by Sencore, August 12. • Service familiarization on the SVS-990 VCR with a handscanner, presented by Toshiba America, August 12. For more information, write to NPEC '89, 2708 W. Berry St., Fort Worth, TX 76109, or call 817-921-9061. •

GIGO MIMIC Servicing tikchnology

Electronic Servicing & Technology is edited for ser-vicing professionals who service consumer elec-tronics equipment. This includes service techni-cians, field service personnel and avid servicing enthusiasts who repair and maintain audio, video, computer and other consumer electronics equipment.

EDITORIAL Nils Conrad Persson, Editor Carl Babcoke, Consumer Servicing Consultant Tom Cook, Senior Managing Editor Alisa Carter. Associate Editor Andrew Naugher. Editorial Assistant

CONSULTING EDITORS

Homer L. Davidson, TV Servicing Consultant Christopher H. Fenton, Circuit Fabrication Consultant Victor Meeldijk, Components Consultant Kirk G. Vistain, Audio Consultant Sam Wilson, Electronics Theory Consultant William J. Lynott, Business Consultant

ART Kevin Callahan, Creative Director Barbara Miles, Graphic Designer

BUSINESS Cameron Bishop, Group Vice President Eric Jacobson, Group Publisher Greg Garrison, Sales Manager Marcia Durrett, Marketing Director Evelyn Hornaday, Promotions Manager Darren Sextro, Promotions Coordinator Dee Unger, Advertising Business Manager

Catherine Grawe, Advertising Coordinator

ADVERTISING Greg Garrison, 913-888-466a

ADMINISTRATION R.J. Hancock, President Chuck Rash, Corporate Circulation Director Sandra Stewart. Circulation Director Donna Schlagle, Circulation Manager Customer Service, 913-541-6628

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Member, Audit Bureau of Circulation

Member, American Business Press

Member, Electronic Servicing Dealers Association

CORRESPONDENCE Editorial, advertising and circulation correspondence should be addressed to: PO. Box 12901, Overland Park, KS 66212-9981 (a suburb of Kansas City. MO); 913-888-4664. Home office tax: 913-541-6697 Home office telex 42-4156 INTERTEC OLPK

SUBSCRIPTION PRICES: one year. $19.49: two years. $3298 in the USA and its possessions. Foreign countries: one year. $2349. two years. S36 98. Single copy price: $2.50; back copies. $3.00. Adjustment necessitated by subscription ter-mination to single copy rate. Allow 6 to 8 weeks for new subscriptions.

PHOTOCOPY RIGHTS: Permission to photocopy for internal or personal use is granted by Intertec Publishing Corp. for libraries and others registered with Copyright Clearance Cen-ter (CCC), provided the base fee of $2 per copy of article is paid directly to CCC, 21 Congress St., Salem, MA 01970. Special requests should be addressed to Eric Jacobson, publisher. ISSN 0278-9922 $2.00 + 0.00

Elechnok Seeking & Technology (ISSN 0278-9922) is pub-lished monthly for $19.49 per year by Intertec Publishing Corp.. 9221 Ouivira Road. Overland Park. KS 66215. Second-class postage paid at Shawnee Mission, KS and additional mailing offices. POSTMASTER: Send address changes to ELECTRONIC SERVICING & TECHNOLOGY. P.O. Box 12960, Overland Park, KS 66212 1989 All rights reserved.

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Setting up an electronics servicing workbench By Conrad Persson

Today, with technology changing almost continuously, it takes almost a constant effort to remain aware of the current technologies and to be equipped to diagnose and service them. Given the rapid pace of technological

advance today, it might not be a bad idea to look at the tools, test equipment and accessories on your workbench as often as once a year to see if it's time to add or replace something. Of course, many of the old tools and test equipment still perform the function they were designed to do, but much of the new technology

either hand wired or based on printed-circuit boards with wide traces, the type of lighting available at the service bench wasn't really critical. Today, with vanishingly thin circuit traces and tiny, surface-mounted components, it's dif-ficult to see the smallest connections even at noon in full sun. Given the am-bient lighting available at many elec-tronics service benches, it's a wonder that the technician can see well enough to find the test points to probe, or to remove and replace components. With today's tiny circuits, if techni-

cians are going to be effective, every bench needs good general lighting, task lighting and magnification.

requires more sophisticated servicing equipment, and there is now a require-ment for more ancillary equipment than ever before.

Lighting and other visual equipment Back in the good old days, when most

consumer electronics products were

Persson is editor of ES&T.

ESD protection You can't see it, you can't smell it, you

can't taste it, and you often can't feel it, but it's lurking in every servicing facili-ty, just waiting for an opportunity to damage or destroy a sensitive compo-

nent. It is electrostatic discharge (ESD), and today it is a common cause of failures in consumer electronics prod-ucts. Take a look at the schematic diagram of any of today's sophisticated electronics products found in the home: TV, CD player, VCR, microwave oven. Have you seen one lately that doesn't feature at least one IC? Not every IC is static-sensitive, but

many of them are. As discussed in the article "Implementing An Electrostatic Discharge Awareness Program" (see page 44 of this issue), in many cases it doesn't take much to damage or destroy some of these components. The voltage threshold at which a human can detect an electrostatic discharge is around 4,000V. Some sensitive components will be damaged by discharges in the range of one-tenth of this magnitude. It should be clear, then, that the presence or absence of crackling discharges is no guide as to whether ESD protection is required. The answer to this problem is clear

and compelling: Every consumer elec-tronics product, every circuit board and every component should be treated as if it's susceptible to ESD damage. Every bench position and every tool kit for servicing consumer electronics products should be equipped with antistatic wrist straps and antistatic mats. Plastic materials such as styrene-foam cups and cigarette, cookie and cracker wrappers, which are capable of generating and holding a static-electric charge, should be banished from the work bench. Every technician should be instructed in the use of antistatic products and in the importance of keeping static-generating products away from elettronics that are opened up for servicing.

Test equipment It's probably possible to still get by

in electronics servicing with a simple DMM, a 20MHz scope and a few other


simple pieces of test equipment. However, today's sophisticated con-sumer electronics products almost cry out for sophisticated tools and test equipment to service them. For exam-ple, in his book "Troubleshooting and Repairing Compact Disc Players," published by Tab Books, Homer David-son recommends the following list of test products if you want to service com-pact disc players:

• a dual-trace oscilloscope • an optical power meter • a digital multimeter • a low-frequency AF oscillator • a signal generator • a capacitance meter • a frequency counter • test discs • special tools, filter adjustment cir-cuits, manufacturers' special jigs, a wrist strap, etc.

The same is true with VCR repair. Take a look at any VCR servicing manual. If you want to get serious about servicing them, you might consider pur-chasing from a list of test gear like this one from a Quasar VCR service manual:

• a VHS alignment tape • a tape back-tension meter • a reel table-height fixture • a dial torque gauge • a tension-post adjusting plate • a post adjustment plate • a retaining ring remover • an H-position adjustment fixture • a fine adjustment screwdriver • a post adjustment screwdriver • a V-hold adjustment tool • a lock screw wrench

If your preference runs to servicing computers, here's another list: a disk drive exerciser, logic probes and pulsers, logic test clips and a lot more.

In addition to the test equipment, there are such things as diagnostic disks that can make servicing computers and peripherals much easier and faster.

Cleaning supplies and other chemicals

These days, many consumer elec-tronics products, such as VCRs and camcorders, are actually elec-tromechanical devices. You also have computer floppy disk drives with mov-ing parts that wear and break, and sen-sing heads and other mechanical com-ponents that are subjected to wear and travel of the magnetic medium. As a result, many service calls require little more than thorough cleaning of the heads or other parts of the tape path. This kind of service requires the right

kinds of supplies and techniques, which should be readily available at the bench or in the portable tool kit. For example, if you will be servicing VCRs, you will want to have available the right kind of cleaning aids and appropriate cleaning liquids such as isopropyl alcohol or Freon TF. You don't want to clean a VCR with cloth, cotton swabs or any other kind of material that might leave lint or any other kind of residue. The two materials generally recognized as appropriate for cleaning VCR heads and tape paths are chamois and plastic foam. Both of these materials are available in sticks or swabs, onto which you spray the cleaning liquid, then carefully wipe the heads and transport parts clean. There are also cleaning tapes for

VCRs and cleaning disks for computer disk drives. From the information avail-able, it appears that most cleaning disks for computer disk drives are safe to use. In the case of VCR cleaning tapes, we used to say forget them. However, there are now at least one or two (and possibly more) that seem to be garnering a reputation for being safe and effective. Choose among these products careful-

ly. Some of them are thought to induce the very problems they are supposed to eliminate.

Microfiche readers Servicing technicians who rely entire-

ly on paper servicing documentation are finding that they are using huge volumes of room just to house the filing cabinets that hold the manufacturers' servicing literature and Sams Photofact folders. However, most manufacturers now of-fer their service literature on microfiche. Storing microfiche takes up far less

room than does storing paper manuals and schematics. There has been some objection in the

past to the use of microfiche, but some servicers who have converted to microfiche wouldn't do otherwise. One of the objections has been the cost of the microfiche reader. Yes, they cost as much as a few hundred dollars, but the small storage space for microfiche


III A

REPRINTS Interested in ordering article reprints out of this or another issue?* Reprints can be excellent learning tools for your technical staff and great marketing tools for your sales staff. Call or write Kelly Hawthorne at Intertec Publishing Corp., P.O. Box 12901, Overland Park, KS 66212; (913) 888-4664.

• Minimum order 500 copies.

• A

Equipment for

a well-stocked workbench

ESD protection: Wrist strap Antistatic mat Antistatic holders

Lighting

Magnifying lens

Test equipment and accessories: ac leakage tester Multimeter Oscilloscope Vectorscope High-voltage probe Logic analyzer Disk-drive exerciser Video-camera light box Test-lead kits Digital probes/pulsers Current tracers Logic test clips Break-out box VCR test devices: tape-tension gauge, spindle gauge

Computer diagnostic software Distortion analyzer Frequency counter Function generator Gauges Field-strength meter Signal-level meter Microwave leakage tester Semiconductor tester Spectrum analyzer

Tools: Screwdrivers

Pliers Wrenches/nutdrivers Wire cutters Wire strippers Crimping tools Drill/reamer Computer keycap puller

Accessories/miscellaneous: Isolation transformer Variable voltage transformer Holding fixtures/vises Ventilation system Microfiche viewer Vacuum cleaner Inspection mirrors CRT testers/restorers

Soldering tools: Soldering iron/station Solder Flux Desoldering tools: Solder sucker, etc.

Desoldering braid IC insertion/extraction tools Printed circuit track repair kits

Chemicals/cleaning supplies: Coolant spray Tuner/control cleaner Video/audio head-cleaning solvents

Computer disk-drive head-cleaning disks

Lint-free swabs Screen cleaning wipes

eliminates the necessity of purchasing several filing cabinets at $100 to $200 each, so the overall result is a smaller, not larger, investment.

Ventilation products Every day, research is finding that the

human system is more susceptible than anyone realized to the deleterious effects of all kinds of chemicals used in manufacturing and servicing. The average servicing facility uses a host of these chemicals: solder that generates objectionable smoke when it's applied, cleaning solvents, coolant sprays, resins and more. If a service shop can't afford to provide fume hoods to vent these fumes directly to the outdoors, it might

make sense to at least provide fans to keep these vapors from collecting in locations where the air is stagnant.

Keeping up with the changes The workplace continues to become

a scene of increased sophistication. Manufacturing plants are now bristling with robots, automatic machinery and sophisticated control systems. Offices abound with computers and other sophisticated products to make workers more productive. Servicing has changed just as much as manufacturing facilities and offices, and it's important for serv-icing technicians to have at their disposal the latest equipment to get the job done safely and efficiently. •


New Smart Scope makes troubleshooting trouble-free When you're looking for trouble, the new 100 MHz Tek 2247A will help you find it—fast. With its integrated counter/timer, Auto

Setup, unique Smart-Cursors TM and voltmeter, the 2247A makes short work of the measure-ments you need most. Time-saving automa-

tion and ease of use are built into every measure-

ment routine. The 2247A gives you one-button setup, storage and recall of up to 20 setups, time and voltage cursors, plus on-screen readouts. It also measures rise/fall time and propagation delay auto-matically, with counter accuracy to 0.001%. Best of all is the price: only $2795! This is the most exten-sive set of capabilities ever

assembled in a low-cost scope. And it's backed by Tek's standard 3-year warranty on parts and labor including the CRT.

The built-in counter/timer/ voltmeter automatically calcu-lates and displays more than 11 different voltage and time measurements.

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Copyright .1989 Tektronix. Inc All rights resented TAD 947

Troubleshooting Tips

Symptom: Rapidly flashing screen, sound fluctuation. Set ID: RCA CTC 108A Sams Photofact: 1937-3

Just when you think you've seen every kind of strange problem, along comes one that's different from anything you've ever run into. This situation occurred for me with

an RCA CTC 108A. The sight and sound coming from this TV were so weird they were intimidating. By instinct, I im-mediately pulled the plug. After a scratch or two of the skull, I turned the set back on for a short time to try to determine just what it was I was look-ing at. The flashing of the screen was so

rapid I couldn't decide whether it was high voltage, which would also affect the 26V scan-derived sound supply, or video information flickering on and off. Using the high-voltage probe at the

CRT anode showed a steady 24kV. Col-

1 L2502 212pH

C250 .—.---101/F

lector voltage at Q412 horizontal output transistor was a solid 119V as per spec on Photofact 1937, folder 3. This meas-urement ruled out problems with either the high or the low voltage. I turned the set on and off for short

periods of time to observe the symptom while minimizing the possibility of causing any damage. I noted that the LED channel display did not always display a numeral. I pulled the IF cable link out of the

tuner. As I expected, the sound and video signal disappeared, but also — a bonus — the fluctuating screen was gone. The TV displayed a solid raster. I injected a video signal with 4.5MHz

sound carrier at the IF link cable. The result was a good pattern on screen with a steady 4.5MHz sound tone. Without a doubt, the problem was in the tuner. A good number of technicians would

be intimidated with one of these all-electronic tuners in general use today and would simply put away the

LED CHANNEL DISPLAY

C2541 1,000pF

I

U2503 LED DRIVER

13

RESOLDER LARGER THAN NORMAL LEADS

C2534 TO.014F

\ R2501 616Q 2W

CR C2512 2,504 T 470pF

— 16V

U2501 FREQ. SYNTH.

CR2503

TP2503 fb--/

schematic, remove the tuner and send it away for repair. This method is not always prudent because it will delay the repair, and you'll be left with another set cluttering up the place. I don't advocate getting out the did-

dle stick and adjusting everything in sight. With the present solid-state design and its low operating voltages, factory adjustments in the critical areas general-ly remain stable for years. The fault usually will be a defective component (generally an IC or capacitor), or it might be one of a surprisingly large number of cold solder joints and defec-tive cable connections. The longer a given set has been in service, the greater is the likelihood of such a defect show-ing up. Some of these electronic tuners, such

as the Zenith 175-5101 microprocessor remote, are certainly intimidating with their maze of connecting cables. In con-trast, this RCA tuner, consisting of two modules, MSC 006A and MST 005A,

KEYBOARD

U2502 OP-AMP/ BANDSAW

TP2505

TP2502

• C2520 0.047pF

TP2501 19V

J2 MSC

R2502 470Q 2W

CR2506

CR2505 I 0

19V

—60V PULSE

Figure 1. The symptoms with this RCA CTC 108A were a rapidly flashing screen and fluctuating sound. When no other leads panned out, the servicer finally looked for a cold solder joint in R2501 and R2502, the only components with larger-than-normal leads.


is a honey to service. The two modules, held together by a few screws and a minimum of connect-ing cables, separate nicely and can be serviced without any additional exten-sion cables. Limited repairs can be undertaken by merely following the same common-sense approach used dai-ly on any digital equipment. The approach here was to trace the

symptom most apparent and easiest to follow on the schematic. The channel display was intermittent, so it stands to reason that the same intermittent was also causing the video signal to fluctuate. The schematic for module MSC 006A

showed that the display panel was powered by the 8.7V supply derived from —60V pulses at plug J2-MSC5, rectified by CR2503 and filtered by 470µF C2509. Voltages were as follows: test point 2504, 5.1V (OK); test point 2505, 28V (OK); test point 2501, 19V (OK).

Test point 2503 read 6.4V. This meas-urement didn't appear to be low enough to cause complete outage of the display, but because the 8.7V source fed only the display, I opened the circuit at L2502 to see if the display panel was loading down the circuit. This action had no ef-fect. I checked C2509 for leakage. It was normal. A logic probe at point Y indicated a logic low for the keyboard master-slave with any button depressed. Everything seemed to be correct. Looking at the schematic, I decided

to take some advice from way back: "When everything seems to check OK but nothing is working right, eyeball the components with the larger-than-normal leads." Only two components fit that description in this portion of the TV cir-cuitry: R2501, a 6.60, 2W resistor; and R2502, a 4700, 2W resistor. I didn't bother to check the values on these two resistors because TP2504 and TP2505 were upstream and the voltages at these test points were OK.

I inspected the solder joints on these two resistors under a magnifying glass, and they appeared to be fine. Never-theless, I heated up the soldering iron and resoldered both ends of each resistor. Once I had finished resoldering, I

turned the set on and immediately two things happened: A perfect picture ap-peared on screen, and a big grin ap-peared on my face. The channel display was a nice, bright numeral 2 and the sound was fine. In retrospect, because I resoldered

both resistors at the same time, the ques-tion arises — which of the two had the cold solder joint that caused the prob-lem? R502 is the voltage source for the tuning control voltage, but no doubt it was R2501, the supply going to the keyboard, U2501 (the frequency syn-thesis IC), and U2503 (the LED chan-nel display driver IC). Frank P. Stoklosa Southgate, MI

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Servicing

scan-rectified

voltage sources By Homer L. Davidson

A built-in fault of all scan-rectified B+ sources is the certainty that they will stop producing voltages anytime the horizontal deflection ceases. Also, when start-up and shut-down fitnctions are added, the circuit operations become highly interactive and complicated. We recommend that you study these prob-lems step-by-step in articles such as this where nine different circuits are examined.

During the past 10 years, most TV manufacturers have obtained some or all low B+ voltages from circuits that rec-tify horizontal pulses (not 60Hz sine

Davidson is ihc TV servicing consultant for ES&T.

waves as in the past) usually taken from windings of the flyback transformers. Small transistors require low-voltage B+ supplies, and these various voltages are produced by rectification of the pulses from several windings having dif-ferent numbers of turns. This method eliminates the unwanted heat otherwise emitted by B+ dropping resistors. Defects and repairs of typical low-voltage B+ sources will be discussed in this article.

Preliminary troubleshooting A dc-voltage supply can develop one

or more defects internally, or defects can occur in a circuit that draws current from a dcV supply. Either condition

Figure 1. A Truetone model CNR4019B was missing both high voltage and sound. R957 tested nearly open, thus reducing the +46V to +7.1V. R957 was replaced along with diode Y957 on the suspicion that it previously had caused the overload that ruined R957. Other deflection-powered supplies were not affected.

usually reduces the dc-output voltage from that supply. Therefore, for the first troubleshooting steps, we should deter-mine whether the problem originates in the voltage supply or in its loads. Sometimes the picture or sound quali-

ty can point to a defect in the video, chroma, vertical or sound circuits. In these cases, measure the B+ voltages that feed the circuit. Some defects produce a black screen,

perhaps from a loss of high voltage. However, many defects are not in the horizontal-deflection system even when the high voltage is missing. In those cases, it might be necessary to find out whether the receiver is in shut-down. If it is in shut-down, the next step is deter-mining whether the shut-down is caused by excessive high voltage. When the high voltage is not excessive, the search brings us to the low-voltage sources. Ex-cessive load on a source can produce shut-down because of the resulting heavy load on the flyback system and the horizontal-output transistor. Alternatively, an overload on a low-voltage source might stop or degrade the performance of one signal circuit because the B+ voltage was too low, but it might not cause shut-down or stop the horizontal deflection. This localizes the problem. Remember, as stated in previous ar-

ticles, deflection-derived B+ voltage supplies depend on normal horizontal-deflection operation. However, with many solid-state models, horizontal deflection cannot function until the horizontal oscillator and driver stages have B+ dc voltage. Unfortunately, the low-voltage supplies cannot have voltage without normal deflection, so the oscillator and driver remain dead. To break the impasse, a start-up circuit sup-plies B+ voltages to oscillator and driver for a brief time after ac power is


Multiple and interconnected low-voltages

Although the RCA CIC111 low-voltage power supplies appear very complicated, they are not when taken separately. The key to understanding these first five dcV supplies is CR107, which produces the workhorse +25.1V source and the two others derived from it. CR107 conducts to ground only the most negative parts of the pin-I3 pulse/scan waveform from the T402 flyback. After the waveform's negative parts are connected to ground by CRIO7's conduction, the remainder of the waveform (including the signal at pin 11, which is the supply's voltage-output terminal) is totally positive and ready for filtering by C119. (Remember, CR107 operates in the scan-rectification mode. Therefore, the dc output voltage is lower than if the polarity of the signal were to be inverted.) This rectification of the signal's negative peaks is an inversion of the usual circuit as shown previously in Figure 1, where the diode conducts only during the most positive peaks of the in-put waveform. (By the way, both circuits are different forms of clamping.) A capacitance-input voltage doubler is

formed by C124, CR112 and CR105. In most circuits, CR112 would return to ground, but here it returns to the +25.1V supply. thus increasing the doubler's out-put dc voltage by +25.1V. Without the in-verted supply's +25.1V, the doubler's +211V output voltage would be reduced to +186V. Coupling capacitor CI23, diode CRIO9

and diode CR110 compose the second

Figure 2. In this chassis, five positive dc voltage supplies are obtained from one flyback Winding. In addition, two transistor/zener regulators operate with power from the work-horse +25V supply. Another flyback winding, diode CR108 and a 1pF filter capacitor supply 5V to several circuits. From this one flyback winding come two voltage doublers.

voltage-doubler circuit. It is similar to the other doubler except the coupling capacitance is smaller and CRIO9 returns to ground, not to the +25.1V source. For these two reasons, the second doubler's dc output of only +64V is lower than the first doubler's output. The remainder of the schematic is con-

ventional, with the +20.5V source com-

ing from the +25.IV source via R604. Also, the +I6.5V source comes from the +25.1V source except through a regulator using series-pass Q600, which has its out-put voltage determined by zener CR600. For the 5V source, the circuit is sim-

ple and conventional. Notice the polari-ty of diode CRIO8 for producing negative dc voltage.


first applied. This voltage kick-starts the oscillator and driver functions that trig-ger horizontal deflection, thus providing high voltage and the low-voltage B+ sources that power the oscillator and driver for continuous normal operation. The following case histories show

typical circuits and problems.

No high voltage, no sound Symptoms of no high voltage and no

sound were noticed in a Truetone model GEC4019B-08 portable color TV. Voltage tests showed higher than normal dc voltage at the horizontal-output tran-sistor's collector, but no dc voltage at the

Remember that defective components in low-voltage, horizontal-derived B+ supplies can cause a multitude of different symptoms. Unless the problem's location is unmistakable, first

perform quick tests on the low-voltage supplies.

driver transistor's collector. (See Figure 1.) The path of the driver's collector voltage was checked back to the +46V supply produced from flyback power. Although normal voltage should have been +46V, only +7.1V was measured at C955. Diode Y957 tested OK, but because the open in R957 indicated a previous overload, I replaced both. This solved the no-HV/no-sound problem.

Multiple voltage sources One example of multiple and inter-

connected low-voltages is the RCA CTC111 color chassis. (See Figure 2.) Five positive dc voltage supplies are ob-tained from one flyback winding. In ad-dition, two transistor/zener regulators operate with power from the work-horse +25V supply. Another flyback wind-ing, diode CRIO8 and a 1µF filter capacitor supply 5V to several circuits. From this one flyback winding come

two voltage doublers. This type of cir-cuit configuration is a rarity. Also, the essential +25V supply is produced in a circuit that is inverted from the usual practice. If you follow step by step. all these functions should be clear. With power supplies that recut)

horizontal-deflection power, the supply's dc-voltage polarity is determined only

by the rectifying diode's polarity. Voltage from a diode's cathode is positive, but from the anode, the voltage is negative. However, the amount of dc voltage is determined by the pulse/scan polarity. For example, rectification of the sweep waveform's pulse provides far more voltage than rectification from an inverted pulse waveform. This latter is called scan rectification, or rectification of mostly the baseline between pulses. For example, scan rectification via CRIO7 and C119 yields the +25V source, and the higher-voltage +211V and +64.1V supplies are powered from pulse rectification. See Figure 2 in the accompanying sidebar for more infor-mation about these supplies. Leaky or shorted diodes, such as

CR106, CR112, CR107, CR109, CR110 or CR108, cause a severe power-supply overload that can produce shut-down. Of course, a near short in a component that is supplied by a dc-voltage source can also cause shut-down. Open or burned current-limiting resistors, such as R109, R110 or R601, might reduce or eliminate the output of the supply of which they are a part. Open or reduced-capacitance electrolytic-filter capacitors can reduce a supply's dc voltage. A shorted voltage-regulator transistor might increase that supply voltage; a leaky regulator transistor can cause poor regulation of the supply.

Shut-down Shut-down that is delayed a few sec-

onds is usually caused by a shorted diode or filter capacitor or by excessive current drain in a low-voltage supply. Sometimes this situation is called chassis shut-down. By comparison, overloads from a flyback with shorted turns or a shorted horizontal-output transistor usually produce shut-down immediately. This distinction in symp-toms can help you find the problem more quickly. In many RCA color chassis that have

an integrated high-voltage transformer (IHVT), the IHVT flyback can be tested quickly by using an isolated-type variable-ac transformer to supply the ac power. Prepare by shorting across 2.5µF C113 and connecting a jumper wire or test lead between gate and cathode of SCR100, the +130V regulator. Then connect a meter to the horizontal-output transistor's collector (case) and, by us-ing the variable-ac transformer, increase the line voltage from zero up to whatever applies about +80V to the out-put transistor's collector. Scope the col-lector. A normal but lower-amplitude waveform hints at a +130V regulator problem. Excessive ringing or smaller pulses between the correct horizontal-frequency pulses might indicate a severe overload or shorted turns in a IHVT winding. Erratic noise spikes mixed with the normal pulses might show arc-ing of the internal HV diodes. If either ringing or noise spikes are viewed on the scope, replace the IHVT flyback. If the output transistor's collector con-

CR404

CR406

C433 1.-0.001,T 7-

C416 IT ,1 50 F

CR405 R432 L405

0.47c2 — — — — —

C414

* — V V V- -( Y ) ffi

4700F y

SHORTED OPEN

B. —40.9V

ao. +202V

+27.2V FOR HORIZ. OSC. qt.

Figure 3. One of the most common power-supply defects caused shut-down in an RCA CTC92. Diode CR405 shorted, which burned open resistor R432, thus eliminating the +27.2V sup-ply Without the +27.2V supply, the receiver achieves start-up, followed instantly by shut-down.


Figure 4. Low brightness was the major symptom of one Goldstar CNR-845. Several voltage measurements disclosed low voltage from the +16.2V supply, and only +2.2V was measured at the +11.8V supply that powers the horizontal oscillator. Filter capacitor C442 (1,000pF) was found open during tests of filter capacitors. Replacement of C442 increased the brightness, providing a normal picture.

tinues to show distorted waveforms, pro-ceed with the low-voltage ac input. Test the dc voltages of all horizontal-powered B+ sources. They should measure about 65% to 70% of the normal dc-supply voltages. If one supply voltage is low, disconnect the diode rectifier and notice if the output transistor's waveform has become normal. If it is now normal, the diode is defective or there is a severe near-short in the dc-voltage output. An alternative method for testing

suspected diodes is to use the diode test of a DMM to check all rectifier diodes in-circuit. If one appears to be leaky or shorted, disconnect one end and repeat the test. Replace any defective or strong-ly suspected diodes. In an RCA CTC92L chassis, the high

voltage would rise normally, followed by a delayed chassis shut-down. The only symptom was a faint tic-tic sound from the flyback area. Although the IHVT flyback was suspected of internal arc-ing, all low-voltage diodes (CR404, CR405 and CR406 in Figure 3) were checked for shorts or leakages. In the +27.2V source that supplies the horizontal-switch, inverter and buffer transistors, I found CR405 was shorted and 0.47i1 R432 surge resistor was burned open because of the shorted diode. This fault eliminated the +27.2V supply. Indirectly, absence of the +27.2V

supply removed the B+ voltages from the horizontal oscillator switch, inverter and buffer transistors. (Tracing the B+ circuitry is complicated by two supply voltages that are connected through a switching diode to two branches of the start-up circuit.) The 27.2V supply passes through a diode to produce the required +26.5V for the horizontal-buffer transistor; the other path is through a +22V regulator and then through diode CR301 to produce the +21.2V for the oscillator switch and in-verter transistors. Therefore, without the +27.2V supply, the receiver achieves start-up, followed instantly by shut-down because the oscillator and buffer do not have B+ voltages and cannot operate.

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Figure 5. The screen of a Sharp model 19C80 held only one horizontal white line, proving that the vertical deflection was not operating. Vertical-output transistors 0502 and 0503 had no B+ voltages. Rectifier diode D503 was very leaky and R521 current-limiting resistor had increased from the original 220 to about 1600.

INCREASED 602 TO 160c) LEAKY

BACK .7 D503 , +48.5V

FOR VERTICAL

R521 Li.-1 C505 0502 & 0503 22Q

47k,F —

T503 FLYBACK

1 .

8 L501

9

D514 L512

± C537 470,F

go. +23.2V

+23.1V

R552A t C550 750c 4 7 AF 50 = [+4.7V]

+11.38V FOR IC501

c536 OSC. & SYNC

OPEN ,"=I 330,F

Figure 6. Drifting horizontal lock was the problem with a Sony SCC-340A-A chassis. Measurements of the dc voltages located only +4.7V at the +11.38V source that supplies the horizontal-sync stages. Installation of a new C536 capacitor stopped the drift.

Figure 7. A defective CR106 diode reduced the CRT screen voltages in an RCA CTC71A, causing a dim, blurred picture. Replacement of CR106 solved the problem.

Figure 8. Low brightness and a dark left side of the raster were symptoms of the problem with one Panasonic T126-A B&W chassis. A dc voltage test showed that the +105V boost was only +65.5V because peak-reading boost capacitor C420 was open.

This shut-down is from lack of horizon-tal deflection, not from overload. After I replaced CR405 and R432, I

slowly increased the line voltage and was pleased to find that the set resumed normal operation before 120Vac was reached. I allowed the set to operate with full line voltage for the remainder of the day before replacing it in the cabinet.

Brightness problems In most cases, insufficient brightness

is caused by defective video stages, low HV or a weak CRT. But do not overlook the possibility that insufficient low voltage can show symptoms of a too-dark picture, brightness that cannot be turned down or scanning lines on the CRT screen. Some suspects for causing dark pic-

tures include: • a CRT screen voltage that is too low, perhaps from an open isolation resistor or a leaky screen-voltage diode rectifier. • insufficient horizontal-oscillator B+ voltage from an open resistor, a defec-tive filter capacitor or diode rectifier in the B+ supply. One likely cause of excessive

brightness with retrace lines is an open isolation resistor or a leaky diode that produces about +200V for the color-output power transistors. Measure the three transistor's collectors (heat sink). They should be several tens of volts lower than the +200V. In a Goldstar CNR-845 color porta-

ble, only +2.2V was supplied to the horizontal oscillator inside IC301. Tests proved that D441 rectifier and R442, the 5.1f1 isolation resistor, were normal. (See Figure 4.) However, replacement of C442, the 1,000µF peak-reading filter capacitor, restored the +16.2V and +11.8V supplies to the usual performance.

Vertical problems Incorrect dc voltages applied to the

vertical circuits from deflection-powered B+ supplies can produce symptoms of insufficient height, no height (one white horizontal line), ver-tical rolling or picture pulling. One cause of vertical rolling and sync pull-ing of the picture could be insufficient filtering of the low-voltage B+ supplies. On a Sharp model 19C80, the screen

showed only a single horizontal white line, indicating a lack of vertical deflec-tion. Measurements at Q502 and Q503, ' the vertical-output transistors, indicated


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ervicing & Technology

a loss of 13+ voltage from the +48.5V supply. (See Figure 5.) These measure-ments were verified when I traced the voltage source to diode D503 (very leaky) and resistor R521 (increased from 220 to about 1600). Replacement of the diode and resistor restored nor-mal vertical deflection.

Horizontal lines Unwanted horizontal lines in the pic-

ture sometimes are produced by defec-tive filter capacitors or increased-value resistors that bring B+ from a horizontal-deflection-powered source. Sometimes the undesired lines will be at one side of the picture, or the picture will drift out of horizontal lock. First check all supply voltages that are

connected to the IC or transistor horizontal oscillator. The cause of ex-tremely high B+ voltages (not likely) or too low voltages must be identified. During our tests, a Sony SCC-340A-

A began operating with out-of-lock horizontal lines replacing the picture. (See Figure 6.) Before an hour had passed, the picture drifted back into proper locking with a normal picture. The +11.38V source for the horizontal-sync function measured only +4.7V. Diode D514, resistor R552 and coil L501 tested OK. When I paralleled 330AF C536 with another capacitor of equal value, the voltage increased to normal. (Of course, turn off the ac-line power before attaching any large capacitor for test. Otherwise, the voltage

An electronics servicer is using a digital meter to check low-voltage B + from horizontal-deflection power.

supplies that operate

A finger points to an integrated high-voltage transformer (IHVT) that is similar to many in the latest model color TV chassis. All high-voltage diode rectifiers are located inside the transformer (flyback).

surge might damage an IC or transistors that operate from that B+ source.) After C536 was replaced, I could

rotate the RV501 frequency control from end to end without losing horizontal lock. This is proof of excellent and stable locking.

Incorrect screen voltages Symptoms of incorrect screen

voltages include a dark screen with on-ly the highlights visible, or a near-normal picture when the brightness con-trol is at maximum or the screen con-trol has been reset for a higher than nor-mal voltage. In such cases, the first step should be readjusting the color-temperature controls in a recommend-ed set-up procedure for a normal white raster. These adjustments include the screen control, video-drive controls and bias controls. If the picture cannot be brought up to

the usual brightness or if the picture re-mains blurry, suspect and test for incor-rect screen voltages, a defective focus circuit or a weak CRT. On the screen of an RCA CIC71A, the

picture was dark and blurred. Voltage measurements at the CRT socket re-vealed low screen voltage. (See Figure 7.) The screen-voltage circuit was traced back to a +800V supply that was powered by a 1401 flyback winding. When the components were checked, diode CRIO6 measured leaky during ohmmeter tests. When the low dc voltage is measured

at the boost- or screen-voltage source, sections of the raster's left side might be too black. Often the cause of these dark vertical bars at the left is an open filter capacitor in the screen or boost circuit when the circuit is powered by horizon-

The location of SCR100, the SCR regulator, is shown by a pointing finger. Look above and to the right for the flyback transformer in this photograph.


tal pulses. This insufficient filtering pro-duces an unwanted waveform that blanks the left side of the raster. Usually the low voltage and the dark side are caused by an open first filter capacitor, the one at the rectifier. Parallel the suspected capacitor with another capacitor of like value, and notice if the dark section disappears and the brightness increases. The capacitor should be replaced by another of the same (or slightly higher) capacitance. Above the minimum, the capacitance value is not critical. Make certain the voltage rating is sufficiently high to prevent a short. When the open filter capacitor is found in the B+ boost circuit (which has lower voltage than does the screen voltage), the original capacitance value often is 1µF. The left side of the raster was

noticeably dark and the brightness was low in a Panasonic T126-A B&W chassis. (See Figure 8.) Adjustments of all controls did not remove the dark area. Voltage at the CRT cathode was low, and the boost voltage measured on-ly +65.5V because C420 was open. C420 is rated at 1µF, but I replaced it with a siLF capacitor, which removed the dark bar from the left side and in-creased the brightness to normal.

Unusual deflection A 3-inch-wide vertical line was the

only thing visible on the screen of a J.C. Penney CTC72P chassis. The line was visible for about five minutes and then disappeared. The high voltage was very low when measured at the CRT anode. When scoped, the gate waveform of

the trace-switch SCR (ITR101) was nor-mal. (See Figure 9.) The gate dc voltage was 4.5V and the anode tested +4.7V rather than the normal +35V. After a lot of troubleshooting, I located the basic problem in the +207V source: diode CR403 was shorted. I speculated that the shorted diode was loading down the flyback pins 4 and 1 winding, thus preventing the trace switch from operating correctly. A new CR403 produced a full raster

with a good picture.

Summary Overloads in horizontal scan-derived,

low-voltage sources can produce many different symptoms. Excessive overloads across flyback-secondary windings often drive the receiver into shut-down. Very low brightness or ex-cessive brightness that cannot be turned down might be caused by incorrect or

In all horizontal-deflection-powered, low-voltage supplies, always check diodes, current-limiting resistors, bypass capacitors and filter capacitors, looking for opens, shorts and leakages. The servicer in this photo is pointing out a critical capacitor.

Figure 9. Nothing was visible on the screen of a J.C. Penney CTC72P chassis (refer to RCA CTC72 for the schematic) except a single 3-inch-wide VE rtical line. Voltages indicated that the trace-switching SCR was overloaded. A shorted CR403 in the +207V supply was iden-

tified as the problem.

low B+ from a low-voltage source. Horizontal lines in the picture or ver-tical problems can result from defective (usually open) filter capacitors in cer-tain low-voltage supplies. A leaky diode rectifier in a low-

voltage supply might cause shut-down or merely eliminate that voltage. Open electrolytic capacitors can produce lines, shaded areas or critical horizon-tal locking. Burned or open surge resis-tors in a low-voltage supply might eliminate all dc voltage. Defective resis-

tors also can produce low dc voltage. Using the DMM diode test, check

transistors and diodes for shorts, opens or leakages. After a shorted diode is located, check for an open or off-value resistor or an open coil. Remember that defective components

in low-voltage, horizontal-derived B+ supplies can cause a multitude of dif-ferent symptoms. Unless the problem's location is unmistakable, the servicer should first perform quick tests on the low-voltage supplies.


What do you know about electronics?

Voltage phasors By Sam Wilson, CET

You are, no doubt, familiar with the impedance triangle shown in Figure 1. It is drawn — in this case — for a typical RC circuit (also shown in Figure 1). If the impedance triangle is drawn to

scale, the phase angle (0) between the voltage and current in the circuit can be measured on the triangle. The fact that the angle is negative means the voltage lags the current. Current is usually used as the reference because the current in all parts of a series circuit is the same. With the same current flowing

through R and C, the voltage across the capacitor (I x K) is 90° out of phase with the voltage across the resistor (I x R). These voltages are shown as phasors in Figure 2. You may have used the term vectors for these arrows that represent voltages or other quantities. However, a vector has magnitude (size) and direc-tion. The direction is related to the sur-face of the earth, such as NE and SW.

Wilson is the electronics theory consultant for ES&T.

:= PHASE ANGLE

TYPICAL IMPEDANCE TRIANGLE

Figure 1. If the impedance triangle for a typical RC circuit is drawn to scale, the phase angle (0) between the voltage and current can be measured on the triangle. The fact that the angle is negative means the voltage lags the current.

IA

TYPICAL VOLTAGE TRIANGLE

Figure 2. With the same current flowing through R and C, the voltage across the capacitor (I x X) is 90° out of phase with the voltage across the resistor (I x R). These voltages are shown as phasors.

Figure 3. The phasors in Figure 2 can be shown with the voltage on the reference (0°) line. Note the 90° angle between the resistive and capacitive phasors.

ONLY FIVE POINTS ARE SHOWN.

IF ALL POINTS WERE SHOWN, THE SINE WAVE WOULD BE COMPLETELY

TRACED.

Figure 4. Sine-wave voltages can be represented by projecting the tips of the phasors onto a time axis as the phasors are rotated. All sine waves can be represented by phasors.

Phasors have size and a direction at a central point that is sometimes called the origin. This direction is an angle be-tween the phasor and a horizontal reference line. The phasors in Figure 2 can be shown

with the voltage on the reference (0°) line. This is shown in Figure 3. (Note the 90° angle between the resistive and capacitive phasors.) Remember that sine-wave voltages

can be represented by projecting the tips of the phasors onto a time axis as the phasors are rotated. This is shown in Figure 4. The importance of Figure 4 is in the fact that it shows how phasors and sine waves are related. In fact, all sine waves can be represented by phasors. In the following discussion, phasors will be used to illustrate sine-wave relationships in circuits.

Representing an RC differentiator There are several facts to keep in

mind regarding the phasor diagram: • The output of a differentiator is the voltage across the resistor (V.). • In a true differentiating circuit, the voltage across R (V.) must be 90° out of phase with the applied voltage (V). • When you increase the capacitance of a capacitor, you decrease its capacitive reactance. If you make the capacitance infinitely high, you replace C with a straight piece of wire. In the following examples, the applied

voltage (V) is constant. In other words, the length of its phasor is constant. Keeping these things in mind, we will

first try to get the phasor for the voltage across the resistor closer to 90° by in-creasing C. (See Figure 5.) That decreases the capacitive reactance and rotates the resistive phasor toward the applied voltage. You can see that this doesn't work because the phase angle should be getting closer to 90° and all we have accomplished is reducing the phase angle. Next we will try reducing C. That will

increase the capacitor voltage phasor (Ve) and rotate the phasor for the


ATTENTION

VCR TECHNICIANS

,A ATi0.164‘.. Yen RIIPAIR

DECREASING V REDUCES THE PHASE ANGLE. THE LENGTH OF V IS CONSTANT. IT REPRESENTS THE

APPLIED VOLTAGE.

Figure 5. If you increase C to try to get the phasor for the voltage across the resistor closer to 90°, you will decrease the capacitive reactance and rotate the resistive phasor toward the applied voltage. As the figure shows, the phase angle is actually reduced.

voltage across the resistor counter-clockwise. (See Figure 6.) Now we are getting closer to 90°. However, note that the length of the voltage phasor is decreasing. If we go all the way to zero capacitance (an open circuit) and keep the applied voltage the same, the resistive voltage phasor goes to zero. The closer we get to 90° with the resistive phasor, the shorter it becomes. There is no way to get the resistive

phasor positioned at 90° with respect to the applied voltage and, at the same time, have a measurable output voltage. To get a full 90°, the resistive phasor (V.) would have to be reduced to zero! In a differentiating circuit, the output

voltage is taken across R, so the 90° phase condition can only take place when the output of the differentiating circuit is zero and, at the same time, the resultant phasor (V.) no longer exists. All of the applied voltage, in that case, would be across the capacitor. The message here is clear: You can't

get true differentiation from an RC cir-cuit. However, you can get very close.

The op-amp differentiator By adding an operational amplifier,

INCREASING V. INCREASES THE PHASE ANGLE. HOWEVER, IT

DECREASES THE OUTPUT VOLTAGE ACROSS R.

V.

V — v

Figure 6. This diagram shows whether reduc-ing C will make the phasor for the voltage across the resistor closer to 90°. Reducing C will increase the capacitor voltage phasor (Vc) and rotate the phasor for the voltage across the resistor counterclockwise. However, note that the closer you get to 90° with the resistive phasor, the shorter it becomes.

the differentiator becomes a better cir-cuit. This arrangement is shown in Figure 7. As I have pointed out in previous ar-

ticles and in my monographs, op-amp circuits can always be analyzed on the basis of the virtual ground. The loca-tion of this point is illustrated in Figure 7. The op-amp will always do whatever

is necessary to keep the virtual ground at OV. Consider what happens when a pulse

is applied to the input of that circuit. This situation is shown in Figure 8. At point (a), the voltage rises rapidly to point (b). That, in turn, produces a rapid, positive-going voltage at the vir-tual ground (VG). To get that voltage back to OV, the op-amp feeds a pulse from the output to the virtual ground. The feedback pulse is negative, so

when it is added to the positive rise from the input, it cancels the pulse. That keeps the virtual ground at OV. The op-posite feedback pulse occurs when the input voltage goes from C to D. The polarity of the differentiator out-

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July 1 989 Electronic Servicing & Technclogy 21

Figure 7. With the addition of an op-amp, the differentiator becomes a better circuit. Op-amp circuits can always be analyzed on the basis of the virtual ground. The op-amp will always do whatever is necessary to keep the virtual ground at OV.

Figure 8. When a pulse is applied to the in-put of that circuit, the voltage at point (a) rises rapidly to point (b). That, in turn, produces a rapid, positive-going voltage at the virtual ground (VG). To get that voltage back to OV, the op-amp feeds a pulse from the output to the virtual ground. Because the feedback pulse is negative, it cancels the pulse when it is added to the positive rise from the input.

Figure 9. The gain of an op-amp circuit is roughly equal to the feedback impedance divided by the input impedance. In the tradi-tional amplifier, the voltage gain (A,) is given by the equation Av

Figure 10. To keep the circuit shown in Figure 7 from breaking into oscillation at higher fre-quencies, you must reduce the amplifier gain. In this revised circuit, the input resistor (F11) Increases the input impedance. The feedback capacitor (Cf) decreases the feedback im-pedance as the input frequency is increased. The overall result is a decrease in gain and a reduced tendency to oscillate.

put is the reverse of what you would get in a simple R-C circuit. However, the shape of the output signal is correct. The output signal would have to be in-verted to get the correct polarity.

An improved version The circuit in Figure 7 works well in

theory, but when you build one, you find that it has a nasty habit of breaking into oscillation at higher frequencies. That is easy to understand. The gain of an op-amp circuit is

roughly equal to the feedback im-pedance divided by the input im-pedance. In the traditional amplifier in Figure 9, the voltage gain (AO is given by the equation

= —RIR, In the circuit shown in Figure 7, the

input impedance decreases (because of the lower capacitive reactance) as the frequency goes up. At high frequencies, the input impedance is very low, so the ratio of the feedback impedance to the input impedance becomes very high. That results in a very high gain. If you have a function generator, you

can easily demonstrate the frequency in-stability of the circuit in Figure 7. Use a 0.05µF capacitor and a 2.21c1/ feedback resistor. Start at 11cHz with a triangular input wave (not a sawtooth). If you're having a good day, a

triangular-wave input should produce a square-wave output. As you increase the frequency, the leading edge of the square wave will overshoot. A further increase will cause ringing at the leading edge. That indicates that oscillation is taking place. How do they get around that problem?

They reduce the amplifier gain. The re-vised circuit is shown in Figure 10. The input resistor (12.1) increases the

input impedance. The feedback capacitor (Cf) decreases the feedback impedance as the input frequency is increased. The overall result is a decrease in gain

and a reduced tendency to oscillate.

Found and lost I have sent many, many letters to

technician friends trying to locate two technicians I knew in the past. My phone bill looks like the city directory. For all of you who promised to help

— I found Dan Loper a couple of months ago. (It turns out that he only looks in his mailbox once every six months.) I still haven't found Bob Rosandich. •

Feedback

The good old days Re: "Hope for Better Days:' your

April 1989 editorial, I believe the bet-ter days have been here all the time. My own common sense tells me one

thing about TV — the picture tube is the next thing to go in a very short time. There goes the section that is and ever was the most failure-prone item. I'm sure that the most failure-prone

item of the future will be the audio out-put section. We had needed about 75W to make the picture, about 8W to make the sound, and about 3W to handle everything else. Those 450W color TVs are going to come down to about 15W. I am dime you realize what that means. Also, witness an article that describes

the making of a solid film for elec-trolytic capacitors instead of the wet film that was used. There goes the capacitors we replace by the handful each month. What have we got left? Well, there's

the lightning storms (I rub my hands at the approach of a thunderstorm); the ac-cidental spillage of a soft drink into the works; the curiosity of the precious sib-lings; the invasion of electronics into everything; the reluctance of consumers to learn the mind-boggling fancy controls. I have and always will service

anything that comes into the store. I've even got a business name to reflect what I do: Eugene's Carry-In. Just about anybody will gamble a bit

of money to get their favorite item repaired. There's your chance! Get a deposit of reasonable proportions to pay for your efforts to look at the equipment, and be very honest with the owner. I get a turn-down rate of about 10% and have been paid for it. Eugene Spooner, CET, AAS Charlotte, NC

Tracking the sun I read with interest Mr. Kluge's arti-

cle, "Understanding Sun Transit Ef-fects," published in the February 1989 issue of ES&T. He specified for three latitudes the peak dates, spring and fall, for the effects. He further noted that, barring some celestial upheaval, these peak dates would be the same each year. Being an ex-science teacher, I was

bothered by this contention and con-sulted with Dr. Ira Dubins, professor of earth sciences at our campus, who was similarly perplexed. He concluded that


there was an apparent failure to consider variations in the vernal and autumnal equinoxes. He provided the following information:

Equinoxes

1987

March 21, 3:52 a.m. Sept. 23, 1:45 p.m.

1988

March 20. 9:39 a.m. Sept. 22. 7:29 p.m.

1989

March 20, 3:28 p.m. Sept. 23, 1:20 a.m.

1990

March 20, 9:19 p.m. Sept. 23, 6:55 a.m.

It should be concluded that if the sun's crossing of the equator can vary over nearly a 3-day period, the location of the sun at a particular latitude in that same year will be subject to the same variation. In light of this fact, the peak dates to which Mr. Kluge referred can-not be the same each year. Joseph S. Gardiner Director, Instructional Resources Center

State University of New York Oneonta, NY

Thank vu for your interest in my arti-cle. The point you make — that the equinox can vary over nearly a 3-day period — is a valid one. Dr. Dubins also is correct in concluding that I failed to consider these variations of the vernal and autumnal equinoxes when defining the peak days. However, the point I would like to

make is this: The total period during which the danger exists to an operator can extend from six to seven days. The peak day is important only in that it defines the week during which the operator should beware of intense solar flux impinging on the feedhom. It behooves the operator to be cognizant of the feedhom's shadow during this week-long period if the antenna is pointed toward the sun. From the figures you provided in your

letter, the maximum peak-day variation from 1987 to 1990 is only 18 hours, 16

minutes; the minimum variation is less than 6 hours. Nevertheless, I'm sure that the readers ofES&T still appreciate this additional information you have offered. James E. Kluge

Computers for small businesses I follow Mr. Lynott's Business Cor-

ner with much interest; because I run a "tiny" 2-man operation, I usually find it helpful and enlightening. I must, however, disagree with the views he ex-pressed on the column, "Using the Computer in the Shop," published in May 1989. I. like most, started on a practically

non-existent budget. Spending $2,000 on a computer system seemed unreasonable and was out of the ques-tion. Being a computer enthusiast and having worked in the field, I realized the great advantage of having one to help out in the shop. I find that the "now seriously outdated" 8086- and 8088-based systems are going very, very cheap — some as low as M O and even cheaper if you are handy enough to put it together yourself. Think of the uses you might have for a shop computer. I keep track of the sets in the shop and their status; I organize the calls for the day; I keep all the expenses we have in there, as well as the income. I have a small database to keep a "help" file. with common failures of certain models. And lastly, it functions as a word pro-cessor. I could not think of any applica-tion that would be so crucial to the operation as to NEED a hard drive — a 40Mbyte drive, no less. It's nice to have one and you can't compare the ac-cess speed and the convenience, but it\ hardly a must. There's enough software out there to

take us well into the next century. Again, I fail to see the need to shave 50µs of the access time with an updated version of the same program. There are excellent databases, spreadsheets and word processor software available for the "outdated" 8086/8088 machines at very reasonable prices. I get the feeling Mr. Lynott is

overlooking the really small guys, like my partner and I. We also want to run our business competently and be suc-cessful. Obviously, a 2-man shop can't afford to spend $2,000 on a printer, let alone up to $5,000 for a system.

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Electronic Servicing & Technology 23 July 1989

Feedback

I run my business on what Mr. Lynott (and most of the civilized world) would consider a toy. I'm using a Commodore 64 with an Okidata printer and two 1.3M floppy drives. The software is mostly homebrew. Marcos Virdo Brooklyn, NY

Many thanks for your thoughtful let-ter. I appreciate you taking the time from your business to write. Be assured that I'm not "overlooking the small guy. -

I 'm one myself, and Business Corner is specifically aimed at the small elec-tronics service company. Your points are well-taken, par-

ticularly from the standpoint of someone like yourself who is computer-literate and capable of writing your own soft-ware for basic tasks. It is, as you have proven, possible for a talented person to put together a minimum, entry-level system for less than the amounts I discussed in my column. However, I must stand by my comments for several reasons. My work with service dealers centers

around one basic goal: growth in sales and profits. The systems you mentioned as being available for as little as $500 or less are available at that price for the very reason that they are limited in their capacity to accommodate growth beyond the most basic functions. Although such a system may seem adequate while your business is so small, I suspect that it won't be long before you will be look-ing around for a system that will sup-port all of your business needs, par-ticularly if you enjoy the growth that I hope is in your future. I wish you could meet a few of the service dealers I know who put together the lowest priced system they could find for their businesses, only to scrap them in favor of systems that were more appropriate (and profitable) soon after. In my view, a computer system for a

service dealer is a tool just like a scope or a signal generator. It's always possi-ble to go the minimum price route, but that is usually not the best choice. I want to stress again that my column did not recommend an advanced computer system that would cost many thousands of dollars. I do feel, however, that one step above the barest minimum will be the best long-term investment. William Lynott •

Test your electronics knowledge

By Sam \Nilson, CFI'

NOTE: There may be more than one correct choice for the multiple-choice questions.

I. What is another name for a beta-squared amplifier?

2. Which of the following are not characteristics of transformer-coupled amplifiers? A. low cost B. impedance matching C. can be tuned to a range of frequencies D. step up or step down voltage E. blocks dc

3. Which of the following are not disadvantages of direct-coupled amplifiers? A. level shifting B. power-supply stability problems C. temperature stability problems D. poor low-frequency response E. ripple in the power supply can cause serious burn problems at audio frequencies

4. Which of the following are char-acteristics of JFET amplifiers? A. low partition noise B. low Johnson noise C. high input impedance D. high input capacitance E. high gate current

5. Connect the transistors in Figure A into a Darlington configuration.

Wilson is the electronics theory consultant for ES&T.

6. Write the equation for impedam_ e matching in a transformer.

7. If you increase the gain of an amplifier, you automatically

the bandwidth.

8. Gate current in a properly operating JFET amplifier is A. dependent on V DD • B. dependent on V DS • C. dependent on VG.,. D. None of these choices is correct.

9. Use of degenerative feedback causes A. a decrease in amplifier gain. B. a reduction of noise and distortion. C. an increase in amplifier bandwith D. All of the above.

10. Negative dc feedback is used to A. increase the bandwidth. B. reduce the gain. C. stabilize the operating point. D. change the phase.

Answers are on page 37.


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RCA CTC135 SIGNAL CIRCUIT SCHEMATIC

Product safety should be consiaered when not have the same safety characteristics as found on other Profax pages. component replacement is made in any area recommended in factory service information of an electronics product. A star next to a may create shock, fire, excessive x-radiation All integrated circuits and many other component symbol number designates corn- or other hazards. semiconductors are electrostatically sensitive ponents in which safety is of special and require special handling techniques. significance. It is recommended that only ex- This schematic is for the use of qualified act cataloged parts be used for replacement technicians only. This instrument contains no Callouts next to wiring plugs indicate connec-of these components. user-serviceable parts. tions to other schematics.

Use of substitute replacement parts that do The other portions of this schematic may be

0301 6303 !F 7700 Are

C300 1000

Ii 301 T F8301 L301 .132,A 14309i P 3 8 C301

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s 5600 61116317 S

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180 1000 5 35V

1303

6319 1800

RCA CTC135 SIGNAL CIRCUIT SCHEMATIC

Product safety should be considered when not have the same safety characteristics as found on other Profax pages. component replacement is made in any area recommended in factory service information of an electronics product. A star next to a may create shock, fire, excessive x-radiation All integrated circuits and many other component symbol number designates com- or other hazards, semiconductors are electrostatically sensitive ponents in which safety is of special and require special handling techniques. significance. It is recommended that only ex- This schematic is for the use of qualified act cataloged parts be used for replacement technicians only. This instrument contains no Callouts next to wiring plugs indicate connec-of these components. user-serviceable parts. tions to other schematics.

Use of substitute replacement parts that do The other portions of this schematic may be

0302 v1c€0 Mc

CF 301

8320 620

'1310

C312„ C328 (32-61

.91/4

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CONP_O_L1E VIDEO _

50 80

Copyright 1989, Electronic Servicing 8 Technology, P.O. Box 12901, Ovedand Park, KS 66212

70 PA REM-14 OR FY 14," .77 TUN N6 SYSTEM 5 USED

3051 pnimis NannulaVu',,,S rg!riviPINWOR 3051

RCA CTC135 DEFLECTION/POWER SUPPLY SCHEMATIC

Product safety should be considered when component replacement is made in any area of an electronics product. A star next to a component symbol number designates com-ponents in which safety is of special significance. It is recommended that only ex-act cataloged parts be used for replacement of these components.

Use of substitute replacement parts that do not have the same safety characteristics as recommended in factory service information may create shock, fire, excessive x-radiation or other hazards.

This schematic is for the use of qualified technicians only. This instrument contains no user-serviceable parts.

The other portions of this schematic may be found on other Profax pages.

All integrated circuits and many other semiconductors are electrostatically sensitive and require special handling techniques.

Callouts next to wiring plugs indicate connec-tions to other schematics.

SCHEMATIC NOTE5. 1. ALL CAPACITORS ARE 50V, EXCEPT WHERE INDICATED. 2, ALL RESISTORS ARE 1/4W 5%, EXCEPT WHERE INDICATED. 3. CAPACITANCE VALUES 1.0 AND ABOVE ARE IN pf, CAPACITANCE VALUES BELOW I 0 ARE IN F. EXCEPT WHERE INDICATED.

4. RESISTANCE VALUES ARE IN OHMS, K. X 1000. 5.4 DENOTES CHASSIS GROUND.

6. VOLTAGES MEASURED WITH SIGNAL APPLIED. AND SHOULD HOLD WITHIN 10%.

7. “AvErOW75 TAKEN WITH Kola RAINBOW SIGNAL APPLIED. EXCEPT WHERE NOTED.


DEFLECTION

COMPOSITE VIDEO

SYNC

6601 C603 300 1pF

6602 ii330K C602 1 1000,A

46 OV 32-F

7P 1

CR601

C6011 6603 I pF 3.91441

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57

56

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3.45 1402, ..) ..../.. • a 1 "A".. H. P IN 1 6412 C427 -+. R429 Il 000T C402_-

(30-F) 470301 R405 2201 1 C405 3000 1/ear .022

i

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C404 6431 R430 12% 33K , TO 1/2W E402 1/ew IF 60

59

C407 .0082

TP411

4.590 63 VCO IN

Y401 ..-- -10t

6403 CERAMIC 1000 RESONATOR 1/81.1

✓ -T1 77113-1 I is

6400 620 I AM. 2% 4. 92V

C403-1- 2400 $ 6404,

1000i 1/8W 5% 2% 4.920

TP403 ( C409 - 100T 5%44

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6424 1000

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62 VCO IN

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TO E513 (9-H) I DEFLECTI ON

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R513 S UF I 20 C504], 2.2oF (501 *

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1/Bw 2.2AF i/ew E502 3 , R503 PART I ISO

TP 10 1403 R409 6.8 ph I Spew

61 05 330% I /26 -1 96)/

0104 Pu.SE 6104 REG 1000

A ALL INTEGRATED CIRCUITS AND MANY OTHER SEMICON-

.6.11- DOCTORS ARE ELECTROSTATF CALLY SENSITIVE AND REQUIRE SPECIAL HANDLING TECHNIQUES OESC NIED WOO -ELECTROSTATI-CALLY SENSITIVE (ES) DEVICES- IN THE SAFETY 1110 SERVICING PRECAUTIONS POUCATION.

CALLOUTS NEXT TO WIRING PLUGS IN-DICATE CONNECTIONS TO OTHER SCHEMATICS

PRODUCT SOFTY NOTI COMPONENTS 111TH A (.1 HAVE ORE. CIAL CHARACTERISTICS IMPORTANT TO SAFETY BEFORE REPLACING ANY Of THESE COMPONENTS READ CAREFULLY THE PRO DUCT SAFETY NOTICE IN THIS SERVICE DATA DO NOT DEGRADE THE SAFETY OF THE SET THROUGH IMPROP. ER SERVICING

73V-~

4120V (27-0)

* R112 75%

1/211 is

* * * R133 6132 6131 6130 6139 4640 75% 150% 680%

1- PA-R1 OF - -1 1/711,1% tiew 1/116 1 1/81.1 PW RC 21 Ell 3 E1032% 2X TO

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1

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$ 1 5K R1 0111

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0401 C410 HOR I 27 DRIVER

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110n

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36

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P 1 18

5.650

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6.870

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HEAT 51 I• 0402

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START PULSE (106

CR1 I S .120V (26-6)

C415

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R415 1402 E 1000 1/211

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1160

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1.2kV • 2%

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C112 680

CR1 1; -3 1

TP110

R144 4.7 1/2w 11

12

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R113 Tp/R119 OR RIG 16 cp c )1 07 TP120

• :34 C120 1500 F.t.,114, 25.1V .1Rio3

1 L -134700 047

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CI 22 F8104 TR221010; I/81d 1/2W •

1000

116v

CR105 _

6.20,2K

•

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2833411-011718-00-JK-P9DEF1350

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S.CR 101150 F8101

Li 03 200 ph 2

E107 C125

120VC1 62 0 R136 270 26

CI 23 , *C121 : 0001

(34-11) EI 01 E111 TO

(34-6)

1500 SOOV

EI 02 (112 9

II

II

II

II

II

II

II

II

II

II

1 I

E712

NOR

R129 77K

6 2y

C114 680

CR109

TO R431 (19-E)

R127 75 7V

CR110 4 3V

10 1 El 20 TO 16 2%

CRlIl (36-C] £S013

4.70 16, 2%

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3 I

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3051 M HO! Manufacturers schminshcs Ri m pRomm 3051

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PART OF

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1R5035 BUFFER

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RED BIAS

R5028 220 i/Ow TP54:11 51.R5041

27° 5.66V °'7V- 76031$

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9:11 R5042 DRIVER -„ 5.63V

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ES016 1 ES006

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12.0V

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R5011 1000 12.011 1/8W

BL 7P E ouip rc,112 05003

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6E5014

SCREEN

TO * R4210 1 5

[3(41-5H1) 1 ja

0

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LI N T .033i__.. TO

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R322 100 7d £109

•

TP405 CR302 R414 12vt. 920 CR403 1W, 5% 74

R413 6200 36

R407 6200 sw 81E401

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TP112

* C I I a'51_. 0,0sei

C3161 C320 1. .01 1 f r

CR402 -t C420.I C408

. OV, 2%1186°

L703 3.9µ1+

.26V SOURCE

.12V SOURCE

TP115

C11:I C117 1 1000 /222%F i

C11 61

.6.8V SOURCE

.9V8 SOURCE

TO C716 (15-0)

F.S.R.A.SE(*) J302-6

£105 (1-13)

E104 F.S.PULSE(-) J302-1

(1 -D)

SOURCE

E110 TO E5010 (36-0

6. VOLTAGES MEASURED WITH SIGNAL APPLIED AND SHOULD HOLD WITHIN 10%.

7. WAVEFORMS TAKEN WITH KEYED RAINBOW SIGNAL APPLIED,EXCEPT WHERE NOTED.

470µF 200V

C104 680 1KV

CR103

-A 70 (loll EISI E152 *C105 * E1Il.. (27 -61 • 0 680 R102

.

i 1KV 470K 1/26.10K

TO £S012 (37-C)

SCHEMATIC NOTES.

2. ALL RESISTORS ARE 1/4W SS, EXCEPT WHERE INDICATED. 1GAU 122COIL I. ALL CAPACITORS ARE SOV, EXCEPT WHERE INDICATED.

3. CAPACITANCE VALUES 1.0 AND ABOVE ARE IN pF,

EXCEPT WHERE INDICATED. CAPACITANCE VALUES BELOW 1.0 ARE IN µF, USED WITH MTTOO r

404 4. RESISTANCE VALUES ARE IN OHMS, K. X 1000.

W RR2B

L 01

J104 C.

J11103

2 0

TO

(5 7117,2- ". 5 TPACIPME POWER PITT

5

CR151

FPW RR2A .1104A:

RL101 *

J104

5.4, DENOTES CHASSIS GROUND.

• •

3 TP116 ------ I

R101 .26V * (32-E1 GI) 3,9 RT101

76

1 * C102 680 1KV

70 STAND BY

ó P102 POWER PITT

411 b102 I

* * 1 R1S1 R152. 2200 7200' SW SW

USED WITH mTTOOS, TMA012

P101

"HOT" CHASS I 5

JW104

5 0

USED WITH 111129

USED WITH H MO

PIOIA

L101

, LC2

F101 „,‘„, 4AMP P109

8: 4 1:AC

WIDE BLADE SIDE OF POWER CORD

JULY 1989 RCA CTC135 COLOR TV


Product safety should be considered when component replacement is made in any area of an electronics product. A star next to a component symbol number designates com-ponents in which safety is of special significance. It is recommended that only exact catalog-ed parts be used for replacement of these components.

Use of substitute replacement parts that do not have the same safety characteristics as recommended in factory service information may create shock, fire, excessive x-radiation or other hazards.

This schematic is for the use of qualified technicians only. This instrument contains no * user-serviceable parts.

The other portions of this schematic may be found on other Profax pages.

All integrated circuits and many other semiconductors are electrostatically sensitive and require special handling techniques.

Callouts next to wiring plugs indicate connections to other schematics.

Reprinted by permission of Thomson Consumer Electronics Copyright 1989, Electronic Servicing II Technology, P.O. Box 12901, Overland Park, KS 66212

schematics Manufacturers' RBFAH ES414„

July 1989 Schematic

HITACHI CT2066 color TV 3050

RCA CTC135 color TV 3051

Reprinted by permission of Thomson Consumer Electronics

Copyright 1989, Electronic Servicing 8 Technology, P.O. Box 12901, Overland Park, KS 88212

Answers to the quiz

Questions are on page 24. 1. Darlington amplifier. The name comes from the fact that the beta of the Darlington pair is equal to the betas of each of the two transistors in the pair multiplied together. If the transistors are identical — or nearly identical — the beta of the combina-tion is beta squared.

2. A — low cost. All the other choices are characteristics of transformer-coupled amplifiers.

3. D — poor low-frequency re-sponse. All the other choices are disadvantages of direct coupling.

4. A, C and D — low partition noise, high input impedance and high input capacitance. These are typical char-acteristics of the JFET as an amplifier.

5. See Figure B.

6. (MINX = 4/4. (This assumes 100% flux linkage.)

7. Decrease. Gain and bandwidth is called the gain/bandwidth product. It is a constant, so if you increase one, you automatically decrease the other.

8. D — None of the choices. There isn't supposed to be a gate current.

9. D — All of the choices are char-acteristics of degenerative feedback.

10. A, B and C — increase the band-width, reduce the gain and stabilize the operating point. Negative feed-back is the same as degenerative feedback.

Call PTS 800 Express toll free. Order direct from the world's largest inventory of quality replacement parts for T.V.'s and VCR's. One convenient source. All makes. All models. Quality backed by the industries best warranty. Just say "charge it". Call today to order or to receive your free replacement parts catalog.

1.

C T D a 'sr EXPRESS 1-800-333-PTS1=

VKA



Servicing

Zenith microcomputers

Part I: The backplane

II) John A. Ross

The Zenith microcomputer is an IBM-compatible personal computer that use a backplane type of design rather than a motherboard. All circuitry for the computer is contained on modular printed circuit boards that are intercon-nected via an interconnection backplane at the back of the computer. This setup is in contrast to IBM and compatible computers that have the processor. memory and other circuitry on a master motherboard, which also contains sockets into which other circuit boards, such as the monitor interface, printer in-terface and modem, are plugged. To open the Zenith computer up for

inspection or servicing, remove the metal top cover. To remove the cover, unscrew the seven machine screws. Two screws attach on each side of the cover while three screws fasten to the back of the cover. After removing the screws, slide the cover toward the rear of the microcomputer and gently lift the cover up. Removing the cover exposes the backplane, power-supply module, at least four printed circuit cards, disk drives and interconnecting cables. Referring to Figure 1, some differ-

ences between the Zenith microcom-puters and some other name-brand microcomputers become readily appar-ent. Zenith computers are designed to be easily serviced. Although this block diagram features an early Z-158PC ser-ies microcomputer, Zenith continues to follow this formula in their present line of desk-top microcomputers. Instead of employing the commonly

used motherboard concept in the Z-158 and other models, Zenith uses a back-plane as an interconnection between the various cards that make up the micro-computer designs. As a matter of note, the motherboard concept surfaces in dif-

Ross is a technical writer and a microcomputer consul-tant for Fort Hays State University. Hays. KS.

62-PIN CONNECTOR SOCKETS

BACKPLANE

I.

ni +5 PSG +12 —12 —5

0 0 0 0 0

DIAGNOSTIC b) LEDs

me.

FROM +5Vdc POWER — +12Vdc SUPPLY — GND

HARD DISK DRIVE

CONTROLLER CARD

OPTIONAL — CARD SLOT

OPTIONAL — CARD SLOT

OPTIONAL CARD SLOT

OPTIONAL CARD SLOT

VIDEO CARD CARD

CPU/MEMORY CARD

HARD DISK DRIVE

FLOPPY DISK DRIVE CONTROLLER

POWER SUPPLY

+12Vdc TO HARD +5Vdc DISK DRIVE GND

KEYBOARD

Figure 1. Instead of employing the commonly used motherboard concept in the Z-158 and other models, Zenith uses a backplare as an interconnection between the various cards that make up the microcomputer designs.


BACKPLANE -5Vdc FILTER CAPACITORS REGULATOR

C101 C102 C103 C104 C105 C106

—0, —0+

0.

csi ET.

—0, 0+

ET.

- 0 +

0.

4.0

C107 C108 C117

0+ +0 R101

C119 - =.0 R102

r-

—0+ -0, —0 , - 0+ - 0, - 0. - 0+ - 0+ C109 C110 C111 C112 C113 C114 C115 C116

FILTER CAPACITORS

P109

Ui

-1UN-0 R103

R104

R105

15

P110

C118 DIAGNOSTIC LEDs

5Vdc

-12Vdc

12Vdc

PSG

+5Vdc

Figure 2. The backplane contains two Molex connectors, five LED indicators and their respec-tive current-limiting and voltage-dropping resistors, a -5Vdc regulator, filter capacitors and eight input/output (1/01 expansion slots. P110, a 15-pin Molex connector, couples the backplane to the power supply of the microcomputer.

P110 SYSTEM POWER CONNECTOR

+5Vdc .411

-12Vdc .6

+12Vdc

+5Vdc

14

11

15

12

SYSTEM GROUND

Figure 3. The pin-out diagram shows that three voltages — +5Vdc. +12Vdc and -12Vdc — and the system ground connect from the power supply through the connector to the

backplane.

ferent series of Zenith microcomputers.

The backplane configuration Pictured in Figure 2, the backplane

contains two Molex connectors, five LED indicators and their respective current-limiting and voltage-dropping resistors, a —5Vdc regulator, filter capacitors and eight input/output (I/O) expansion slots. Although this backplane resembles an ordinary circuit board, it features multilayer construc-tion. Used on the other printed circuit cards in the microcomputer as well, this type of construction calls for soldering and desoldering techniques different from those techniques used for the com-mon single-layer printed circuit boards. Technicians may find an excellent reference to these techniques in the May 1987, August 1987 and the May 1988 issues of Electronic Servicing & Technology. Located in the middle-right side of the

backplane, a 15-pin Molex connector couples the backplane to the power sup-ply of the microcomputer. Figure 2 shows the physical location of this con-nector, labeled P110. Figure 3 displays the pin-out diagram. Three voltages — +5Vdc, +12Vdc and —12Vdc — and the system ground connect from the power supply through the connector to the backplane. On the backplane, the +5Vdc is connected via lines B3 and B29, the —12Vdc is connected through line B7 and the +12Vdc is connected via line B9. Lines Bl, BIO, and B31 establish the ground plane. Because of the need for heavy

current-carrying capacity, this design uses multiple sets of pins for the ground and for two of the three voltages. Along with the 15-pin connector, the backplane also contains a smaller Molex connec-tor. Because the video driver board of the microcomputer requires +12Vdc for operation. Zenith built in a separate


2-pin connector, labeled as P109, for this purpose.

The LEI) indicators Five LED indicators give the techni-

cian a feel for the start-up voltages of the microcomputer. A glance at four of the indicators, one labeled for each of the three power supply voltages and the regulator voltage, gives an indication of the presence or absence of those voltages. To check for voltage tolerance, you need only to look at the fifth in-dicator, labeled PSG for power supply good. A lit PSG indicator shows that each voltage falls within the required ±3% tolerance. As we will see later, you can't rely on these indicators as a cure-all, but only as a preliminary diagnostic aid. Each LED operates on a steady

2.5Vdc at 20mA supplied through current-limiting and voltage-dropping resistors R101 through R105. Figure 4 schematically depicts this operation. Labeled as R101 and R102 respectively, 5600 and 1,5000 resistors connect the cathodes of D101 and D102 to the re-quired voltage bus. Two other 5600 and 1,5000 resistors, R103 and R105, con-nect the anodes of D103 and D104 to sys-tem ground. This return to ground

allows the LEDs to properly sense the +5Vdc and +12Vdc signals. Also, +5Vdc is connected through another 5600 resistor connected in series to the anode of D104. As mentioned in an earlier paragraph,

Zenith uses D104 as the power supply good diagnostic indicator. While the microcomputer goes through the various stages of power-up, the design of the cir-cuit allows a few hundred seconds for power supply stabilization. Until the power supply outputs have reached com-plete stabilization, the cathode remains at a potential of +5Vdc. This potential, supplied through pin 10 of P110, keeps the LED extinguished. If the protective sensing circuitry of the power supply "sees" normal operating voltages, the sensing circuitry pulls pin 10 to near ground potential. At near ground poten-tial, the LED lights and indicates nor-mal power supply operation. Consequently, normal operation also

means triggering the only output sup-ply voltage generated on the backplane. Integrated circuit U101 supplies a regulated —5Vdc to the bus connector at pin Bfi through a 47µF filter capacitor labeled C118. U101 derives the —5Vdc from the —12Vdc line. Again referring to Figure 4, pin 0 of the regulator sends

—5Vdc to the parallel bus connector. As pin G returns the signal to system ground, pin I receives the —12Vdc filtered through a 0.01µF capacitor, C117, and a 2.2µF capacitor, C119.

The signal bus All of this takes us to the signal bus.

On one level, the signal bus simply serves as an interconnect between the power supply, the backplane, and the CPU, video, disk-controller, I/O and memory cards. Physically, the eight identical 62-pin edge connector sockets, eight filter capacitors and the actual backplane make up the bus. Arranged with 31 pins on each side, labeled Al through A31 and Bl through B31, the connector sockets give the microcom-puter two things: IBM compatibility and the possibility of expansion with addi-tional cards. Room for expansion sets the Z-L58 and other newer models apart from those models in the Zenith line that are constructed around the motherboard design. In a later article, we'll take a closer look at possible ways to expand the capabilities of a microcomputer. Because of the identical nature of the connector sockets, the technician may insert any card in any location. Eight 33µF capacitors, placed between every

TO LINE 135 ON BUS

-5Vdc

TO LINES +5Vdc B3 AND 829

ON BUS .0,

TO LINE 87 ON BUS

-12Vdc

TO LINE +12Vdc 89 ON BUS

-, C118 47,,F 35V

-5Vdc REGULATOR.

R101 R102 2 R103 R105 560S? 1,5013,.,2 560s2

R104 5602

P109

2_1

P110

33 F/10V REPRESENTS EIGHT FILTER CAPACITORS ON BACKPLANE (C101. C103. C105, C107, C110, C112, C114, C116)

Figure 4. Each LED operates on a steady 2.5Vdc at 20mA supplied through current-limiting and voltage-dropping resistors R101 through R105. Labeled as R101 and R102 respectively, 560Q and 1,5000 resistors connect the cathodes of D101 and D102 to the required voltage bus. Two other 5600 and 1,5000 resistors. R103 and R105. connect the anodes of 0103 and D104 to system ground. Also. +5Vdc is con-nected through another 5600 resistor connected in series to the anode of D104. D104 is used as the power supply good diagnostic indicator.


other pair of connector sockets, filter the +5Vdc supply voltage. On a more complex level, the bus

supplies a myriad of data to the in-dividual cards that make up the microcomputer. Unfortunately for most technicians, learning about this data also means learning new terminology. For starters, you will have to learn the ter-minology that describes the bus' eight bits of bidirectional data, twenty address lines, six levels of interrupt, lines for memory, I/O read and write, and clock and timing control. Additionally, the bus provides the aforementioned operating power, a channel check line for memory error checking, and an I/O channel ready line for peripheral devices. Although these terms seem intimidating, a careful examination will show how these functions interact as the microcomputer operates. Compatibility with the IBM design

dictates the type of signals found along the bus connectors. Figure 5 shows the signal lines. At line Al, Zenith employs an I/O channel check signal. Normal-ly, the technician will find the I/O ch.ck signal at an active high level. If an er-ror, indicating either a problem with memory or other I/O devices, appears along the I/O channel, the signal goes to an active low.

The lines of communication For communication between the pro-

cessor, memory and I/O devices, Zenith uses lines A2 through A9 of the connec-tor to transfer eight bits of bidirectional data. Each 8-bit group equals one byte. Two bytes equals a word. Jumping ahead to microprocessors for an instant, a 16-bit processor can transfer either one or two bytes at a time. Internally, a 16-bit processor can work on or process 16-bit data or instructional codes. An 8-bit processor transfers only one byte at a time. Subsequently, we'll examine the more recent 32-bit technology. Not surprisingly, Zenith uses a micro-processor that has a 16-bit internal struc-ture, the 80088, in the 150 series of microcomputers. However, moving back to the bus, they employ an 8-bit data bus. Looking at this data, each line works at an active high. Significance ranges from DO at line A9 as the least significant bit to D7 at line A2 as the most significant bit. Line A10 shows as the I/O channel-

ready line. Again normally operating at an active high level, the line pulls to an active low state to lengthen the I/O or

memory cycle. An active low state oc-curs with the attachment of slower peripheral devices and ensures that the line retains all data. In a normal operating condition, the active low or not ready state can hold for 10 clock cycles or 2.1 ps. Zenith designates line All as the ad-

dress enable line. As with all other signals, this signal normally works at an

active high level. When at an active high, the CPU or any other devices become disabled with the direct memory access controller taking con-trol of the line. With the DMA con-troller controlling the address bus, data bus and the read and write command lines, a direct memory access can take place. This particular operation allows for the transfer of information from the

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Technology 41

GND RESET DRIVE +5Vdc IRQ2 -5Vdc DR02 -12Vdc N.C. +12Vdc GND MEMW MEMR I/O W I/O R DACK3 DRQ3 DACK1 DRO1 DACKO CLOCK IRQ7 IRQ6 IRO5 IRQ4 IRQ3 DACK2 TIC A.L.E. +5Vdc OSC. GND.

81 82 83 B4 135 B6 B7 B8 B9 Blo B11 812 B13 B14 B15 B16 817 B18 B19 820 B21 B22 B23 B24 B25 B26 B27 B28 829 830 B31

62-PIN BACKPLANE CONNECTOR SOCKET

Al A2 A3 A4 45 A6 A7 A8 49 A10

All 412 413 A14 A15 A16 A17 A18 A19 420 A21 A22 423 A24 A25 A26 427 A28 A29 A30 A31

CH.CK. D7 06 05 04 03 D2 D1 DO I/O CH.RDY A.E.N. A19 A18 A17 416 A15 A14 A13 Al2 All A10 A9 48 A7 A6 45 44 A3 A2 Al AO

EIGHT DATA LINES

TWENTY ADDRESS LINES

Figure 5. Compatibility with the IBM design dictates the type of signals found along the bus connectors.

Figure 6. A preliminary check for a possible fault in the backplane connector signal operation involves simply switching the printed circuit cards from location to location. If the fault does not show, clean all edge connector contacts and inspect the backplane for poor solder connections.


processor to the memory. During the operation, the processor writes to the memory by placing data on the bus along with address and control signals. Generally, the microprocessor generates a 16-bit address code that indicates the memory storage location that will receive the data. With the address enable and the memory-write enable ac-tive, the memory performs a write operation and stores the information. On the data bus, line B11 serves as the memory-write enable line and causes the storage of information when operating at an active low condition. Similarly, the memory-read enable

line operates at an active low condition when the processor needs to retrieve data. In this operation, the processor receives either the next instruction code for the executing program or data code from the memory. Starting the opera-tion, the processor sends the data transfer lines into an input mode and places the address location code on the address lines. Sequentially, the memory-read enable signal, found at line B12, reaches an active low state. When the memory-read enable signal reaches the active state, the memory cir-cuit responds by placing the requested binary code on the data transfer lines. After receiving the code, the processor stores the code in an internal instruction register or into a data register. Obvious-ly, the selected register depends on the type of code, program instruction or data sent to the processor.

Getting the processor's attention Taking a closer look at the actual

direct memory-access operation, you will notice several things happening in rapid sequence. When a device initiates a transfer, lines B18, B6, and B16, called the direct memory-access request lines, reach an active high level. At an active high level, the DMA controller receives the request for a data transfer. In turn, the DMA controller sends a signal, called the DMA acknowledge, through lines B17, B26 and B15 to the requesting device. With the designation of "avail-able for user assignment:' line B17 stands unused. Line B26 serves the flop-py disk-drive controller and line B15 serves the hard disk-drive controller. Ef-fectively, the acknowledge signal tells the peripheral device that the DMA con-troller has reached a ready state. Also, the terminal count line, B27, relays a pulse when any direct memory-access channel signal reaches the terminal. To

initiate the memory-refresh cycle, the DMA controller sends a signal through line B19 to the system random access memory. Several important things happen when

a printer, floppy disk drive, hard disk drive or some other peripheral device

A detailed look at the backplane architecture gives the technician an idea of what happens

during the microcomputer system operation. Although the operation detailed in the backplane description occurs within an instant, the technician needs to recognize the action of the

various signals.

requires attention from the processor. Comparatively, the data transfer be-tween the devices and the processor resembles the memory transfer opera-tions. As the name memory-mapped I/O suggests, the processor considers the in-put and output locations as memory locations. Imitating the memory transfer

routine, the processor sends input/out-put on the data transfer lines; it sends an address code on the address lines; and it then enables the I/O write or read signal on lines B13 or B14, respective-ly. Both lines serve as bi-directional lines at an active low state. When at the high or idle state, both lines send an in-put control signal to the processor. Receiving the input control signal from line BB, the processor latches the signal into an internal data register and loads information into the DMA controller. Receiving the input control signal from line B14, the processor begins to read the control registers. At their active states, the signals serve as an output control signal. During the DMA transfer, the signal from line B13 con-trols the loading of data into the peripheral device. When line B14 reaches the active low state, the DMA controller uses the signal to access data from a peripheral device during the direct memory-access write transfer operation. After either the memory or I/O

address-enable occurs, the processor ad-dresses the memory and I/O devices with active high levels on lines Al2 through A31. These twenty address lines provide access to approximately one million memory address locations. Con-secutively numbered down from the most significant bit to the least signifi-cant bit, address line Al2 carries ad-dress bit 19. Address line A31 carries address bit zero. Typically, the DMA controller generates address bits zero through seven and the processor generates address bits eight through 19. As the processor generates addresses, the bus controller sends the address latch-enable signal through line B28. Primarily, this signal latches valid ad-dresses from the processor, but it also acts as another indicator. Acting in series with the address enable signal from line All, the address latch enable signal shows the I/O channel that a valid processor address exists. Three lines remain in the description

of backplane signal lines. Working at an active high level, the reset drive signal at line B2 monitors the system logic. As the microcomputer goes through power-up, the reset drive signal initializes the system logic, synchronizing to the fall-ing edge of the system clock signal. Similarly, if the reset drive signal senses a low power supply condition, it resets the system logic in the same manner. Lines B20 and B30 carry clock and oscillator signals. As line B20 carries the 4.77MHz signal of the system clock, the 14.31818MHz clock signal flows through line B30. When we examine the actual CPU card, we will also take a closer look at the two clock signals. Essentially, a detailed look at the

backplane architecture gives the techni-cian an idea of what happens during the microcomputer system operation. Although the operation detailed in the backplane description occurs within an instant, the technician needs to recognize the action of the various signals. For the technician, a logical troubleshooting procedure depends on a sound knowledge of circuit action. If you look at the troubleshooting flow chart, the need for that knowledge becomes readily apparent. In future ar-ticles of this series, we will discuss the individual functions of each card and the peripheral devices of the Zenith microcomputer. Not surprisingly, as we look at the cards, we will also find ourselves continually referring to the backplane signal operation. II


Implementing an electrostatic

discharge awareness program

You walk across the carpeted room, reach for a door knob and — Zap! — you find yourself on the receiving end of a tiny shock. Nothing particularly extraor-dinary about that. Those little shocks can happen any time and almost anywhere. But in the electronics world they become a far more serious affair because they are a threat to sensitive electronics components. That's why the U.S. military is con-

cerned about it. Information provided by the Office of Public Affairs at Warner Robins Air Logistics Center at Robins Air Force Base, GA, said that the Direc-torate of Maintenance's Airborne Elec-tronics Division is stepping up its efforts to control the hazard known as elec-trostatic discharge (ESD). Its concept, which combines formal ESD training with awareness and protective measures, is expected to lead to a long-term, com-prehensive program to safeguard the vast majority of components in the avionics center. The plans are detailed, right down to the type of floor wax that will be used. Some of the details of that pro-gram are presented here. Adapted by consumer electronics servicing facilities, these measures could reduce damage to ESD-sensitive components and products.

The ESD problem Static electricity is generated whenever

two substances are rubbed together and then separated, or whenever they flow relative to one another, such as when a gas or liquid flows over a solid. The static electricity is stored on non-conductive materials and tends to remain in the localized area of contact, awaiting the opportunity to discharge to the first available ground source. Many of today's electronic components

are susceptible to some degree of damage from electrostatic discharge of 100V or less, and numbers of such static-sensitive components will continue to grow. On a dry day at 1.5% relative humidity, no

activity can be performed, not even the simple act of raising your arm, that will not generate more than IOW. The construction and design features

of modern electronics technology have reduced the size of the components to greatly miniaturized dimensions over all previous technologies. This microminiaturization is increasing the susceptibility of components to damage by ESD. Microminiaturization has resulted in

parts that can be destroyed or damaged by ESD voltages as low as 20V. A per-son can detect a static electric shock only at voltages above 4,000V. Most ESD damage occurs below the

human detection level, and the damage it does is often invisible under the microscope. Sophisticated analysis is re-quired to detect ESD failures, and some do not become apparent until some time has elapsed. These so-called latent ESD failures are malfunctions that occur because of earlier ESD exposure that did not result in an immediate detectable failure. In short, ESD is a serious problem that

calls for serious solutions.

All components are static sensitive Much of the electronics industry has

been treating all of its parts as ESD-sensitive because it is more economical and easier to handle all the parts the same way. Warner Robins ALC will start treating all ESD-sensitive components and its related printed circuits as ESD-sensitive. This new management concept is a total ESD environment. It's an ounce of prevention is worth a

pound of cure approach that focuses on cost-effective ways to enhance reliabili-ty and maintainability.

Training is the key The division started its program with

training, which is offered in two levels. Twenty-five people assigned to the elec-tronic warfare area already have received the formal 3-hour training course, the first level. An estimated 1,700 produc-tion and software workers will receive the first-level training. Second-level training is a videotaped

presentation for management and support staff who do not work on the equipment directly, but who still occasionally come in contact with ESD-sensitive devices. Long-range plans call for the develop-ment of a 40-hour course. Employees completing the training

will receive special decals. The decals of first-level trainees will authorize them

Type

MOSFET JFET CMOS Schottky diode Polar transistor ECL SCR

Table 1. Component static susceptibility

Typical susceptibility level

100V to 200V 140V to 10,000V 250V to 2,000V 300V to 2500V 380V to 750V 500V 680V to 10,000V

Adapted from a paper by the U.S. Air Force.


Understanding static

A static charge is the result of an ex-cess or deficiency of electrons on a sur-face. The relative amount of electron imbalance determines the static charge level. Simply stated, a charge is generated by physical contact between, then separa-tion of, two materials. One surface loses electrons to the other. The types of materials involved and the

speed and duration of motion between them determine the charge level. Common non-conductive plastic packaging materials such as polyethylene, polystyrene or mylar films are particularly prone to this electron imbalance. Even relatively low levels of static elec-

tricity can destroy or degrade certain elec-tronic components. Sensitive devices in-clude metal oxide semiconductor (MOS) devices, junction field-effect transistors (JFEB), diodes, thick-film resistors and various bipolar circuit elements. The typical ranges of static susceptibility for

such devices are listed in Table I. These kinds of devices are manufac-

tured with multiple oxide layers with tolerances measured in millionths of an inch, and they are designed to operate at low voltage levels. Static electricity can create shorts, opens or changes in critical performance values, and the damage may not surface unless the device is called on to operate at or near its rated load An electrostatic discharge event that oc-

curs during the handling of a device is the most obvious form of damage. However, many devices can be ruined or degraded without direct contact or noticeable spark. The key is to protect a component at all times from static charge and voltage fields exceeding its rated breakdown voltage.

Reprinted from the article "Static Control, A Con-tinuous Concern," by Mike Voss of the 3M Static and Electronic Control Division, Austin, TX, published in the May 1988 issue of MSM magazine.

August 7-12, 1989

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to work in areas with ESD-sensitive items. Second-level trainees receive decals that give them access to such areas, but not authorization to work on ESD-sensitive items.

Keep untrained technicians away Another part of the plan is to establish

ESD zones, identified with dots or lines, where sensitive components are handled. Only certified employees will have ac-cess. A prototype is being set up in one production area, and lessons learned there will be applied as the zoning con-cept is developed elsewhere in the avionics complex. Also, standardized storage and packag-

ing procedures will be used to protect items against ESD buildup when they are not being worked on. The ESD plan uses an approach to en-

sure that all program elements are in-tegrated as a system and to reduce the ESD hazards throughout the facility, especially where ESD-sensitive items are handled outside of their protective wrap-pings. The plan considers existing equip-ment and facilities and how they can be effectively converted consistent with the

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ESD control requirements for the sen-sitivity of the items involved. One of the most important aspects of

the ESD plan is education. The most elaborate ESD prevention and handling procedure will not provide the protection needed if personnel are not properly trained in their correct use. Employees are being trained to effec-

tively use materials and equipment and to understand the theory behind many of the ESD procedures. The most impor-tant part of the ESD plan is to inspire a greater sense of awareness and respon-sibility toward ESD damage prevention.

Protecting static-sensitive equipment Much has already been done to pre-

vent ESD damage. For example, items slated for repair are inspected for ESD sensitivity before they are routed to the production areas. ESD-sensitive devices are typically

packaged in two bags. An inner bag of antistatic polyethylene material prevents static buildup. The bag is impregnated with a soapy material that provides a "sweat" layer on the outside of the bag. The outer bag has a thin layer of metal that prevents static from going through the bag. Electronic components are placed on

a table equipped with ESD-protective devices. A conductive mat dissipates static. Production workers wear wrist straps that connect by wire to a ground. Resistors between the straps and ground prevents the possibility of shock. The grounds, which in the avionics center are water pipes or air lines, have to be at a certain depth to be effective. Plastics are hazardous to ESD-

sensitive items because plastic is a purely non-conductive material that can be charged with the slightest friction, heat or pressure. Common items, such as plastic cups and tape, will be removed from ESD-sensitive zones when the full plan is implemented. Plastics commonly found on tool

handles can be used if they are treated with antistatic spray. Such sprays and conditioning foams also figure in the overall control plan. A program such as the one used in the

Air Force ZNiolliCs installation is ex-tremely important because it's possible that they might affect people in a life-threatening situation. It's not as critical in the servicing of consumer electronics products, but it's important, nevertheless, because it could prevent needless, cost-ly damage. •

Products Digital video probe

The DP-100 digital video probe from Tektronix gives the user an analog view of digital data. The user can tap into a data bus, convert the signal to analog and display it on a scope, waveform or picture monitor or a vectorscope. Features include a fully buffered ECL/TTL probe, up to 50MS/s data rates, a precision 10-bit DAC, a switch-able reconstruction filter, and adjustable clock phasing and sync timing.


Roll pouch kit The RP3926 39-piece lab roll pouch

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Waveform monitor/vectorscope The model 5872 combination

waveform monitor/vectorscope from Leader Instruments offers simultaneous vector and waveform display for obser-vation of two video sources on the same screen. Features include sweep rates of

1H, 2H, IV, 2V and 1H MAO, 2H MAG, 1V MAO and 2V MAO; a x5 vertical gain magnifier; chroma and IRE filters that can be inserted on a full-time or line-shared basis; and a switching mode power supply.


BNC connector adapter kit The model 5511 BNC connector

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case interior is fitted with a contoured foam liner to separate and protect the metal adapters.


Aerosol product line The Cramolin aerosol product line

from Caig Laboratories uses only ozone-safe propellants. The fast-acting, de-oxidizing solution cleans, preserves and lubricates metal surfaces, including gold. The solution maintains maximum electrical conductivity to prevent contamination.


Memory chip tester adapter The RAMCHECK 1Mbyte adapter

for the RAMCHECK memory chip tester, manufactured by Aristo Com-puters, can test 1Mbyte, 256K by 4 and 64K by 4 chips in addition to the stan-dard 256K and 64K chips. A bad chip or the correct chip type is identified on the RAMCHECK display. Existing owners get a free EPROM upgrade that provides an improvement in error-detection rate for the standard 256K and 64K chips.


Cleaning/polishing/burnishing kit The All Kit from The Eraser Com-

pany contains a selection of Rush In-dustrial cleaning, polishing and bur-nishing brushes. The kit contains dif-ferent sized stick brushes in coarse- and fine-grade FybRglass; a set of refillable, pen-type brushes; nylon, brass and stainless steel refills; a rotary polishing wheel; palm-held and rotary brushes; two metal, refillable brushes; two small abrasers; and a utility brush for clean-ing hard-to-reach areas. All can be used on metallic and non-metallic surfaces.


Analyzer The LC102 Z-Meter capacitor and in-

ductor analyzer from Sencore tests capacitor values from 1pF to 20F by charging the capacitor through a preci-sion resistor, measuring its time constant and displaying the value on the digital LCD readout. Capacitor leakage is dynamically tested at the operating voltage. When the test is completed, the capacitor is safely discharged. Inductors are also tested dynamically, in or out of circuit, from 1pH to 20H. Features in-


dude a dielectric absorption test, an ESR test and a ringing test. The meter compares results to EIA standards and displays a good or bad indication.


Color pattern generator The Philips PM 5518 TXI color pat-

tern generator, available from John Fluke Mfg., offers full remote control through a standard GPIB/IEEE-488 in-terface for use in automated testing sys-tems. This generator covers TV stan-dards NTSC, PAL and SECAM, as well as PAL N and M standards. The unit features composite video outputs, sound

'as

.L 40 _ - $ 12 di — ci

modulation in dual channel and mono, and special test patterns, including a 250kHz multiburst, a VCR pattern and a demodulation pattern. All available TV and sound modulation can be selected remotely. More than 70 test pat-terns and carrier frequencies between 32MHz and 900MHz can be selected by direct entry at the numeric keyboard or over the GPIB/IEEE-488 interface.


Digital multitester The DM310 digital multitester from Universal Enterprises has a 31/2-digit LCD digital display with 1/2-inch-high numerals. The meter features overrange and low-battery indication, an audible continuity buzzer, 33 ranges, a data-hold button, auto polarity, diode and tran-sistor check function, and a 10Mil in-put impedance on ac and dc voltage ranges. The ruggedized meter can withstand a 7.5-foot drop and offers safety features such as surge voltage pro-tection, resistance and buzzer circuits protected to 250Vac, and fuse protection on all current ranges except 10A.


Digital sampling scope The PCIP-SCOPE from MetraBytes

is a 20MHz digital sampling oscilloscope that provides dual-channel operation, 8-bit vatical resolution and

full input protection. Both channels pro-vide ac and dc input capability. Input signal bandwidth is 10MHz, and the maximum real-time sampling rate is 20MHz, which yields a 5Ons sample period. Effective sampling rates can reach as high as 500MHz. The scope features simple programming, 5mV to 5V input sensitivity, and free software with pop-up control menu.


DMM The SOAR model 3060 DMM,

developed by Carlo Gavazzi In-struments, incorporates a 3,200-count, full-scale analog bar graph, high-speed auto or manual ranging, a diode test, a continuity beeper function, and speed sampling of the 32-segment bar graph display. The DMM is fully protected on all ranges to 450V. It uses dual-slope in-tegration for measuring ac and dc voltages to 450V and resistances from 3000 to 30MO.


Digital decade substituters The IET portable substitution boxes,

available from HMC, are used to set resistance, capacitance and inductance values. The desired value can be dialed in with side-by-side thumbwheel switch-es, which are colored according to the various impedance ranges. The im-pedance values are preset and read directly to avoid mistakes. Four series of substitution boxes are available: RS series sets resistance; CS series sets capacitance; RCS series sets both resis-tance and capacitance; and the LS series sets inductance. The units are also avail-able in precision models.


Circuit tester Vortec has developed a compressed-

air-powered circuit tester that uses —20° air to chill circuit boards, sensors and electronic components. The model 138 circuit tester cools sensors and com-ponents in five to 10 seconds with a stream of cold air that leaves no residue. The cold air outlet is sized to permit targeting of tiny electronic components and circuits. An integral muffler to ex-haust the hot air and an insulated hous-ing allows the unit to never become hot or cold to the touch. Each unit has no moving parts to wear out or maintain

and comes with a filter, regulator and six inches of airline.


Soldering station The model 7050 temperature-con-

trolled soldering station from Endeco offers the convenience and safety of temperature control for users who do not need to meet MIL standards. The unit maintains temperatures with an on/off controller and features a standard three-wire grounded iron with a temperature range of 450°F to 950°F.


Screwdriver The PA 1955 screwdriver from

Paladin has six bits (two Phillips, two slotted and two hex). The driver design allows the user to unscrew the handle cap and select the proper bit, which is stored in the handle when not in use. The ergonomic handle is formed to fit the user's hand to generate more torque. Each handle is injection molded on the shaft during the assembly process to eliminate breakage. Paladin offers a guarantee against breakage on the screwdriver shaft.


Oscilloscopes Beckman Industrial has introduced

three oscilloscopes: the model 9102 (20MHz), model 9104 (40MHz) and model 9016 (60MHz). The scopes are equipped with trigger circuitry that en-sures display stability. A variable hold-off control ensures proper triggering on

complex signals. Each model features A and B sweeps with delay and segment magnification; TV sync coupling for easy video service; a camera-mount CRT bezel, variable scale illumination and single sweep operation for waveform photography; and Z-axis in-put for blanking or intensified markers.



Sym c ur e Symptoms and cures compiled from field reports of recurring troubles

Sears 564.49010250, 564.49020250-251. 564.49060350-351 1 Photofact 2177-2

D012

R103 180kQ

R015 56kY

D010 1S1555

D003 1S1555

LEAKY

D004 EaA01-06SB

Symptom: Shutdown/no voltage regulation. Cure: Replace shorted D003, leaky 0004.

Sears 564.49010250 Photofact 2177-2

C455 + 4.7 F I — 1

•-r•

REPLACE

Symptom: Foldover and loss of vertical deflection at top of picture. Cure: Replace C455. 4.7pF capacitor.

2


/,,,

3

TO CHANNEL TIJNA•GIDOA010

412 All

AIS 17 •

14 ,0

AI,

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Pf

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Symptom: Will not change channels, but will tune. Cure: Replace M51233P.

o.

Sears 564.42101151 4 Photofact 2100-2

112V

C004 220pF

IC001

•

LA5112N ERROR DET-POWER REGULATOR DRIVE

L002

REPLACE

120V

R013 5.600S?

Symptom: No voltage regulation, shutdown. Cure: Replace LA5112N and 0005 (SK9188, Sears 46-13428-3).


SW901

-cflo ON/OFF

POS001 PTC 9.0 c 4, 2

TOTAL COLD

12 D001

111-- 101 —

VDR ERC4-06 001

ROO 1005: 6W

"=-•

28

R002 1.2Y

-‘.A/Vs

C003 470pF L 11 ,

5

R004 821(Q

CHECK AND REPLACE

Symptom: Low dc voltage. Cure: Check and replace C003 if it has reduced capacity.

Sears 564.42072050, 564.42230050 Photofact 1990-1

R448 10,-) 6W

TJ401

C440 47,4F

,N\ REPLACE IF

CAPACITANCE IS REDUCED

Symptom: Picture is half width. Cure: Check C440 for lost capacity.

T-40-31

6 •


Books/Photofact Customize Your Home Entertainment System: TV and VCR Enhancement Projects, by Steve Sokolowski; TAB Books; 288 pages; $15.60 paperback, $24.95 hardbound. The inexpensive projects in this book

allow the reader to have a custom enter-tainment system with improved sound and video. The book also includes a mini-course in basic electronics, em-phasizing development of project-building skills. Enhancements included are noise-reduction systems, graphic equalizers, surround-sound decoders, stereo simulators, a stereo audio con-trol, an audio power meter and a bass boost filter. TAB Books, Blue Ridge Summit, PA 17294-0850; 800-822-8138.

Radio Operator's License Question & Answer Manual, 11th edition, by Milton Kaufman; Hayden Books; 550 pages; $19.95. This manual is a resource for anyone

trying to pass the FCC General Radio-telephone License Exam, Marine Radio

Permit Exam or private industry elec-tronics certification exams. The book uses a question-and-answer format, em-phasizing solid-state circuitry and state-of-the-art radio communications. Hayden Books, a division of Howard W. Sams, 4300 W. 62nd St., Indianapolis, IN 46268; 317-298-5604.

Encyclopedia of Electronic Circuits, volume 2, by Rudolf F. Graf; TAB Books; 744 pages; $29.45 paperback, $60 hardbound. This second volume of practical cir-

cuits includes all new circuit designs, including temperature controls, os-cilloscope circuits, probes, stereo balance circuits, buffers, crystal and RF oscillators, pulse generators and more. An index lists the 728 circuits presented in this volume along with the 1,300 cir-cuits presented in volume I. TAB Books, Blue Ridge Summit, PA 17294-0850; 800-822-8138.

Principles of Digital Audio, second edition, by Ken C. 1Pohlmann; Howard W. Sams; 432 pages; $29.95. This revised edition gives the reader

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a comprehensive look at digital audio, complete with technologies such as CD-I, CD-V and DAT. The book begins with the fundamentals of numbers, sampling and quantizing, and covers topics such as digital audio recording and reproduc-tion, alternative digitization methods, error correction, optical storage and transmission, and the compact disc. Howard W. Sams, 4300 W. 62nd Si, Indianapolis, IN 46268; 317-298-5604.

Understanding Electronics, third edition, by R.H. Warring, edited by G. Randy Slone; TAB Books; 230 pages; $11.60 paperback, $1&95 hardbound. This basic guide to electronics is an

updated edition with redrawn circuit diagrams; a glossary of commonly used electronic equations; and expanded coverage of industrial automation, digital computers and microprocessors, transistors and high-voltage power sup-plies. The 51 circuit projects from earlier editions are also included. TAB Books, Blue Ridge Summit, PA 17294-0850; 800-822-8138. •

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Business Corner

Setting a fair price By William J. Lynott

It's no secret that some electronics servicers have come up against hard times. The increased reliability of to-day's technology and falling prices for new electronics products have combined to put the squeeze on many service dealers, especially those who aren't do-ing a good job of diversifying and marketing. Unfortunately, too many servicers feel

that the solution to this problem is to lower their service rates or maintain rates that are already too low. Some dealers feel that it's only an "ivory tower" theory to suggest that most customers will gladly pay the going rate

as long as they feel they are getting prompt, professional service. As a result, some dealers have con-

vinced themselves that they must manipulate their bills in order to hide their true labor rates, or scrape by on rates that are too low to generate a de-cent profit. If you are among those who feel that way, consider these few obser-

Lynon is president of WI Lynott. Associates. a man-agement consulting firm specializing in profitable ser-vice management and customer satisfaction research.

vations. They are the result of my hav-ing worked as a consultant for dozens of service organizations, large and small, over a period of many years.

Aim for the average customer In my first job as a TV service techni-

cian many years ago, the company I worked for charged $3.95 for a home service call. That's right, $3.95! And I can assure you that complaints about service rates were every bit as prevalent then as they are today. That's just the way it is in the service business. People do not like paying for intangibles, regardless of the price.

There is, of course, a small percen-tage of people who will unrelentingly pursue the cheapest price in town for anything they buy, without regard for any other considerations. These people are out there, no denying that, but it's important to remember that they are but a tiny percentage of your potential customer list. To allow one of your most important business policies to be in-fluenced by such a small minority is simply not a sound business decision.

As often as not, those same people are the sort of customers whose business you are better off without — customers whose business seldom yields a reasonable profit for anyone. At the other end of the scale is that

small percentage of customers who give price hardly more than a passing glance. Getting the best of everything — or at least appearing to — is what is most im-portant to them. It is these people who make it possible for the "premium" labor-rate dealers to exist. I know a number of such dealers and, although my own preferences tend toward a more moderate approach, they seem to have no trouble finding customers. It is in between these two extremes

that you will find the overwhelming ma-jority of all potential customers. These are the people who are willing to pay a reasonable price for what they buy, provided they feel they are getting value and satisfaction for their money. These are the people who represent a secure financial base for the competent and honest service dealer. These are the people for whom both your pricing structure and your policies with regard to customer satisfaction should be fashioned.

Is it the price or the quality? It has long been established by in-

dustry surveys that most customers' complaints that appear to be centered on the price actually have their roots in the customers' unhappiness with the quali-ty of the product or service that was pro-vided. In other words, many complaints that seem to be about price would never have been born if the customer had been given the satisfaction to which he or she was entitled. These are just a few of the reasons

that I feel the way I do about service rates. The service dealer who attempts to get by on labor rates that are anything less than he is entitled to, or who engages in misleading practices in ex-pressing labor rates, is not only doing himself an obvious disservice, but he is also undermining the fiscal health of his business. •


Literature Test instrumentation catalog RAG Electronics is offering a 12-page

guide to new and used electronic test in-strumentation. The used equipment sec-tion features spectrum analyzers, ac and dc power sources, environmental chambers, signal sources and oscilloscopes from Tektronix, Hewlett Packard, Wavetek and others. The new equipment section features selected products from Fluke, Hitachi, Power Designs, PowerVar and more.


PC catalog The 68-page "Personal Computer In-

strumentation Catalog" from Rapid Systems shows the company's complete line of turnkey instruments, including oscilloscopes to 100MHz, real-time FFT spectrum analyzers, signal proc-essing systems, universal 100MHz counters, waveform recorders, educa-tional courses and more.


Workstation service catalog Jensen 's 32-page "Workstation Serv-

ice Catalog" offers products for trouble-shooting, service and repair of data processing equipment. The catalog in-cludes information on the company's workstation tool kits, diagnostic soft-ware, tools and test equipment.


DMM selector guide Beckman Industrial is offering an il-

lustrated selector guide describing the company's line of heavy-duty digital multimeters. The guide covers the HD150 Series, a line of 31/2-digit, heavy-duty, autoranging DMMs.


Watch battery guide Batt-Tronic has published a com-prehensive watch-battery inter-changeability guide that lists more than 1,000 battery numbers from more than 20 manufacturers in alphabetical and numerical order. Each battery number is cross-referenced to the proper Batt-Tronic drawer number. The drawer number system guarantees that any bat-tery in the designated drawer is inter-

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Test equipment catalog A 32-page catalog of electronic testing

and prototyping equipment is now available from Global Specialties. In-cluded in the spring catalog is the com-pany's line of breadboarding products, logic test equipment, power supplies, test instruments and accessories. Also featured is a new line of data com-munications equipment.


Parts catalog MCM Electronics is offering its 176-page catalog containing more than 11,000 parts and components, including more than 500 new items. Among the categories of products offered are semiconductors, TV parts, computer equipment, power centers and regulators, telephone parts and ac-cessories, connectors, tools, batteries, speakers, VCR parts and audio parts.

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Audio Corner

Troubleshooting problems in the

de-emphasis circuit Part I

One of the less well-understood audio circuits is the de-emphasis circuit. Pre-emphasis of higher frequencies at the broadcasting location, accompanied by equal but opposite de-emphasis at the receiver, results in a reduction of noise in FM radio and TV audio. As with any other circuit in an audio system, the de-emphasis circuits can develop faults. A fault in an audio de-emphasis cir-

cuit could manifest itself as abnormal-ly high audio noise levels or, in the case of a complete failure of the de-emphasis circuit, a tinny sound, as if the treble had been boosted all the way up. Here's a little detail about how pre-emphasis and de-emphasis work, and a suggestion on how to diagnose the de-emphasis cir-cuit if you suspect problems in it.

The effects of noise Noise is present in every electronic

system. It interferes with the reception and reproduction of wanted signals. Nature generates noise — electrical storms, solar activity and the stars in-terfere with audio transmission. Human activity also introduces noise because of rapid and random motion of electrons in the molecular structure of electronic components and circuits. These noise sources will limit the performance of any electronic system.

The effects of noise on FM reception From the time an RF signal carrier

is transmitted to the time it is detected by the receiver, the carrier may be modulated by noise. The largest effect will be in changing the amplitude of the carrier. An indirect effect of noise on the frequency is a small carrier devia-tion (phase modulation). The limiter stage (before the FM detector) prevents amplitude changes on the carrier from passing to the receiver's detector stage,

Adapted with permission from Tech Tip #I23, "Understanding Pre-emphasis and De-emphasis," published by Sencore, Sioux Falls. SD.

which is why FM signals are less af-fected by noise than are AM signals. Any phase change of the carrier, however, will be passed to the detector and detected as noise.

Pre-emphasis reduces noise To minimize these indirect phase

modulation effects, the sound level at the output of the FM receiver's detector must be made much larger than the detected noise. The sound volume of an FM detector is proportional to the deviation of the FM carrier. If the audio signals cause a much larger carrier deviation than the indirect noise phase

INDEX IMPROVEMENT

' 1 REF. 2 6dB 3 9.5dB 4 12dB 5 14dB

Figure 1. The S/N ratio will improve at the FM receiver in proportion to the square of the modulation index. The modulation index is the carrier deviation divided by the audio modulating frequency.

changes (during transmission and recep-tion) the noise will not be as noticeable. Actually, the larger the modulation in-dex at the transmitter, the better this signal-to-noise (S/N) ratio will be at the output of the FM receiver. In FM broad-casting, the highest audio frequency will produce a maximum modulation index of 5, but for lower audio frequencies it may be much higher. The S/N ratio is proportional to the square of the modulation index. The highest modula-tion index can increase the S/N ratio by 14dB in FM broadcasting. (See Figure 1.)

The pre-emphasis network S/N ratios can be improved by an in-

crease in the amplification of the higher audio frequencies at the transmitter. Amplification will cause larger carrier deviation at those frequencies and thus better S/N ratios at the receiver. The pre-emphasis network at the transmit-ter increases the amplitude of higher audio frequencies, conforming to a pre-arranged curve, referred to as a 75µs pre-emphasis curve, established by the FCC. (See Figure 2.) The pre-emphasis network at the

transmitter may be a simple RC or LR

TRANSMITTER • R PR EMPHASIS

RC TIME CONSTANT 5 MICROSECONDS

Figure 2. At the transmitter, audio signals are routed through a 75s pre-emphasis network.


of t

FREQUENCY

TRANSISTOR VOLTAGE GAIN & OUTPUT IN mV

PRE-EMPHASIS GAIN

300 1,000 2,120 3,000 5,000 8,000 10,000 15,000

202 221 283 346 512 754 964 1,428

0.1dB 0.9dB 3.0dB 4.8dB 8.2dB 11.8dB 13.7dB 17.0dB

Figure 3. Audio pre-emphasis equires an AL or RC network to increase the amplification of higher audio frequencies to conform to a 7511s pre-emphasis curve.

filter network that will alter the gain of an amplifier to conform to the pre-emphasis curve. The 75/2s is the time constant of the network, which will cause a 3dB increase at the frequency given by the formula F=RxC/2. This frequency will be about 2,120Hz. Figure 3 shows an example of a pre-emphasis circuit and a chart to indicate how the output impedance of the amplifier

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changes the gain of the stage to produce an output that conforms to the 750 curve. Next month, we'll conclude this look

at pre-emphasis and de-emphasis cir-cuits with a closer look at de-emphasis networks, the location of the networks in the circuitry, and the tests that a serv-icer should perform to track down prob-lems in these circuits.

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Computer Corner

IBM personal computer servicing

do's and don'ts By Glenn R. Patsch

Servicing or upgrading a component in a personal computer is much like 1,vorking on other electronic equipment, except there is both a hardware and a software side to everything. When something is not working properly, it might be the hardware or the software (or both) at fault. As with every other type of electronics equipment, there are some do's and don'ts that will save you a lot of aggravation, wasted time and ex-pense if you follow them when you serv-ice personal computers.

ZOO DO unplug the power cable from the computer chassis and turn off the power switch BEFORE opening the cabinet. On rare occasions it may be necessary to check something when the computer is on, but always attempt to fix the prob-lem with the power off first.

DO get the key for the PC/AT or PS/2, or you will not be able to get the chassis cover off. It is possible to crack the case to get inside, but it is also expensive to replace. Many users leave the keys in the lock or leave the unit unlocked.

DO ask if a password has been set up if it is a PS/2 system. All the PS/2 sys-tems can be set up with a password. If you have the key but not the password, you can disconnect the lithium battery for 20 minutes and the system will no longer require a password. However, you will now have to reset the system configuration, which requires the

Busch is a consultant specializing in the selection. evalua-tion and installation of IBM personal computer and com-patible hardware and sollviare,

reference diskette and any additional setup disks for cards added. You can usually use the restore configuration op-tion on the reference diskette to reset the setup information that was lost when the battery was removed.

DO be aware that in many cases, bat-teries inside the computer need to be replaced. The PC and PC/XT may have an optional clock on a plug in card. These cards have small button cells that maintain the time and date when the computer is turned off. A few cards have rechargeable nickel/cadmium batteries. The PC/AT has a lithium battery used to maintain the built-in clock and setup information. The PS/2 has a lithium bat-tery used for the clock and setup infor-mation. These batteries are rated for one year, but they usually last about two years. The clocks are used to maintain a calendar for dating files that are saved on the system. The setup information tells the system what hardware is pres-ent (such as the number of floppy drives and the hard disk size and type).

DO get the diagnostic disk that came with the PC and XT. The PS/2 has a reference diskette. Many users will not have this readily available, so you should have your own. You get the advanced version of the diagnostic software with the IBM maintenance manuals. IBM up-dates these from time to time.

DO obtain the diskette the user places in the a: drive for booting the system if the computer you'll be servicing has on-ly floppy disk drives and no hard disk. On hard disk systems, the operating sys-tem (DOS) is stored on the hard disk. On a system with no hard disk, the operating system must be stored on a floppy disk. This disk is referred to as the boot disk because it is used to "boot-

up" the system every time it is turned on. If this disk is not in the a: drive and

the floppy door is closed when the PC is turned on, the system will bring up BASIC. This causes no end to confusion if you do not realize what has happened. IBM originally intended to offer low priced systems with no floppy or hard disks and let users bring up the system in BASIC. The idea was to save pro-grams on a cassette tape deck. Older PCs have a connector next to the keyboard connector for this purpose. Depending on what you are installing or changing, you may need to modify files (config.sys and autoexec.bat) on the boot disk.

DO be aware that on PCs with a hard disk, if you have a disk in the a: drive when you turn on the system it will at-tempt to boot off of this disk. This method was intended to give you a way to bypass the hard disk in case it is damaged. If you get a message of "non-system disk or disk error," remove the floppy disk from the a: drive and press any key. The system will try again.

DO be aware that when the system is running and you are stuck in a software program, the computer might not re-spond to anything you do at the keyboard. If this situation occurs, you can press the CTRL, ALT and DEL keys simultaneously and the system will reboot (in most but not all cases). This is known as a warm boot and is almost the same as turning off the computer and turning it back on. There are a few situations that will not respond to the warm boot, and the only way to regain control of the computer is to turn it off and then back on with the switch. Always try a warm boot first, however. A warm boot saves some wear and tear


on the computer compared to a cold boot, and it is faster. Many software programs will also

recognize the combination of the CTRL and Break keys and will suspend opera-tion and return you to DOS. This is preferable to the CTRL-ALT-DEL com-bination because it suspends operation of the currently running program but doesn't reboot the computer. This com-bination usually doesn't work with prob-lem programs.

DO be aware that the PC, PC/XT and PC/AT have DIP switches on the system board that may need to be changed de-pending on what you are installing. The PS/2 uses software to configure the system.

DO be aware that some hardware re-quires software changes to be made to the system configuration file (config.sys) to be properly used by the system. Some hardware also requires a change to the bitch file that executes automatically every time the system is turned on or rebooted (autoexec.bat).

DO realize that if you don't understand these guidelines, you need to review PC basics before opening the cover of the computer.

DON'T move a PC with a hard disk unless you are positive that the disk head has been parked with a software utility, or you are absolutely sure that the disk itself has an automatic head-parking feature. If you move the PC and the disk

head was not parked, the head may crash into the magnetic disk surface, damaging it. These surface scratches may cause the disk to lose data. To be safe, the hard disk should be complete-ly backed up using the BACKUP com-mand or a software backup utility that copies the contents of the hard disk to several floppy disks or a tape. The IBM diagnostic diskette for the PC/XT in-cludes a shipdisk command (Ship-disk.com file) for parking the disk head. The IBM PC/AT disks must also be parked. Some of the newer IBM PS/2 systems have drives that automatically park the heads.

DON'T disconnect a PC from a net-work until you properly sign off the net-work. Ask before doing so or you may cause network problems. Most networlcs are set up so each PC has a batch file that accesses the network and another that drops access. Just turning off the power switch does not properly sign off some networks. If you see a coax cable attached to the back of a PC, suspect that it is part of a network and consult with the operator before disconnecting it.

DON'T be intimidated by personal computers. They are very straightfor-ward. Like everything else, they require some education and a little patience.

These suggestions will get you started and save you some time. As with other digital electronic equipment, the per-sonal computer is sensitive to static elec-tricity. Observe precautions if you are changing memory chips, installing a co-processor chip or adding adapter cards. Some of these components are quite ex-pensive to replace if damaged. Avoid touching the edge connectors on the plug-in adapter cards when installing or removing them. •

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Video Corner

Using logic in troubleshooting-Part I By Stewart Leabman

When a technician gets out of school and gets his first electronics servicing job, he often has the tendency to try to memorize different trouble symptoms and their cures. The problem with that method, of course, is the servicer's limited memory. The best way to approach a servicing

problem is to know how different com-ponents and circuits work, pinpoint the area most likely to cause the problem, then think your way through the circuit to the problem component. Using logic in your troubleshooting can speed up your repairs by saving you from wholesale desoldering and replacement. Here are a few case histories that il-lustrate the need to think first and desolder later.

Noisy hi-fl playback Following a circuit in a logical man-

ner is important when you are looking for a problem that seems to have no

Leabman is an electronics servicer in Bensalem. PA.

cause. For example, recently a customer brought in a Mitsubishi HS-43OUR VCR that was exhibiting noisy hi-fl playback. In this case, the problem was not directly caused by any electronic components. It was caused by a strange signal path that does not exist in theory but did exist in practice. The VCR had noisy sound in the hi-

fi mode. The first thing I did was align the audio-FM switching points with an alignment tape. Although the switching points were slightly off, alignment didn't help. It sounded like the RF switching

points were off, but the hi-fl RF envelope was perfect. Looking at con-nector HH, pins 12 and 14 on the hi-fl printed circuit board (PCB), I saw that the audio had 30Hz pulses on both channels. In the right channel, the signal can be

traced back through IC3Z7, pin 7, to IC3Z7, pin 3; back to IC3X3, pin 4, to IC3X3, pin 2; back to IC3Z5, pin 6, to IC3Z5, pin 5; back to IC3X4, pin 14,

Figure 1. Glue that had become conductive was shorting pins 6 and 7 of IC3Z2, creating an unintended path for RF switching pulses that resulted in noisy hi-fi playback in this Mit-subishi HS-43OUR VCR.

to IC3X4, pin 17. The signal was good at pin 17, but it had noise pulses start-ing at the collector of Q3403 after it came out of IC3X4, pin 14. Looking at the base of Q3403, I saw RF switching pulses, but why should there be RF switching pulses there? Tracing back from the base of Q3404 to IC3Z2, pin 7 (see Figure 1), there were the switch-ing pulses at pin 7. That line is called MUTE. Coming

into pin 6 of IC3Z2, RF switching pulses come from connector HX, pin 2. I looked at IC3Z2 from the top of the PCB and found glue on all of the pins. The glue was turning dark brown at the edges, so I wiggled the IC. The noise in the audio disappeared, then reap-peared. The glue apparently had become conductive and was shorting pins 6 and 7 of IC3Z2. After I removed the glue, the unit was repaired.

Dc-dc converter failure The exact cause of a problem is not

always immediately apparent. Again, if you rely on memorizing symptoms and cures, you'll be less able to troubleshoot problems in which the symptoms don't immediately point to a particular prob-lem. This is especially true when the defective part fails because of another not-so-obvious bad part. In this case, the defective part was

overheating and failing because of another bad part. I had been getting quite a few Hitachi/RCA VCRs with the complaint of no display. The reason for the failure has been the same in all of them: There is no output from the dc-dc converter, which supplies several voltages for the clock display and the tuning voltage. In the Hitachi VT-56, for example, the

dc-dc converter is shown as IC1701. (See Figure 2.) In some models, a circuit protector (ICP-N5) is in line with the B+ to the dc-dc converter. In the first unit I saw with this problem, I replaced the dc-dc converter and the set worked


173

-37 5 (-37.5)

El+

3Vac

3Vac

35v

IC1701 dc-dc CONVERTER

40V

GND

C1708 47,F 50V

Figure 2. The dc-dc converter — IC1701 in this Hitachi VT-56 — supplies several voltages for the clock display and the tuning voltage. Open electrolytics, including C1708, can make

IC1701 draw too much current.

fine for about 10 minutes. After that time, the display went out and the dc-dc converter was burned up again. I ordered another dc-dc converter, re-placed it and measured the current draw. It was drawing about 300mA (too much), which was causing it to heat up. I disconnected all the loads from the

converter, and it still drew 300mA. Wait a minute! What's going on here? I re-moved the converter from the VCR, hooked up ground and 18V to the B+ input, then measured the current. It was still 300mA and the converter was get-ting hot. I put the converter back in the VCR, connecting every pin, and measured each pin with my scope. I found that ac was riding on the —35V line, which has C1708, a 47i.LF capacitor, across it. There should not be any ac there. I replaced the capacitor, and the con-

verter's current draw dropped con-siderably. Out of curiosity, I measured the frequency of the converter before

and after I replaced the capacitor and found that it was about 150kHz with the bad capacitor and more than 260kHz with the good capacitor. The problem was the dc-dc converter was running at too low a frequency, causing the ex-cessive current draw in its transformer. Checking the other electrolytics in the

area, I found that they too were bad, no doubt from the heat. I replaced them also and the unit was repaired. Now, every time I get an RCA/Hitachi

VCR with this problem, I find that the same capacitors are bad along with the dc-dc converter. Although I now know the cure to this symptom in this model, knowing how the circuit works helped me avoid a lot of extraneous probing and desoldering. After all, you still have to figure out what the problem is the first time. Next month, we'll show more ex-

amples of how logic in your troubleshooting can help you service VCRs faster.

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SUCCESS Over 25,000 technicians have gained admit-tance worldwide as certified professionals. Let your ticket start opening doors for you.

ISCET offers Journeyman certification in Consumer Electronics, Industrial, Medical, Communications, MATV, Radar, Computer, and Video. For more information, contact the International Society of Certified Elec-tronics Technicians, 2708 West Berry St., Fort Worth, TX 76109 • (817) 921-9101

Name

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Send material about ISCET and becoming certified.

Send one "Study Guide for the Associate Level CET Test!' Enclosed L is $5 1+ $1 postage).

July 1989 Electronic Servicing & Technolcgy 57

Readers' Exchange

NOTICE: AS OF THE OCTO-BER ISSUE, ES&T WILL CHARGE A SMALL FEE FOR READERS' EXCHANGE ITEMS.

To more efficiently process Readers' Ex-change items and assure more timely ad turn-around, the Readers' Exchange department will be turned over to the Classifieds staff as of the October issue. Readers' Exchange items will cost 50 cents per word; Classified ads will continue to cost $1.65 per word. Readers' Ex-change items will continue to cover only Wanted and For Sale items. Specialized heads, such as job opportunities or help wanted, must continue to run in the Classifieds section.

WANTED

105 Sams Photofact folder sets, various sets #4 to #1190; various radio/TV pans; speakers-capacitors; rod antennas; resistors-whewound power resistors, transistors, etc.; 300 radio/TV tubes, new in original boxes. Elmer). Alderman, Route 2 Box 139, Madison, NC 27025.

Service and/or schematic of the Gertch FM devia-tion meter. model DM-1 (this is a battery-operated unit in the bottom portion of the Gertch Hetrodyne model FM-3 frequency meter); the old tube-type Lampkin FM deviation meter, dual-scale, must be reasonable and working. Robert E. Duncan, 1513 Sixth St., Eureka, Cl 95501; 707-442-2794 7p.m. to 11:30 p.m.

Sams TV Photofacts #1832 through #2598, will pay a reasonable price. Prefer response from Florida. Jennings Hanson, 735 Clematis Road, Venice, FL 34293; 813-493-4159 or 813-497-010&

Power transformer for a Zenith TV, part number 95-3250, model Fh2511w, chassis 25hc50; schematic with service manual, will copy or buy. James Gebhardt, 319 Cherry St., Columbia, PA P5I2; 717-684-7348 weekdays before 2 p.m. EST, weekends all day.

Sencore CR70, must be in excellent condition, with all five socket adapters and 390170 universal adapter. Will pay a reasonable price.././. Newman, 819 Connie Ave., Wheelersburg, OH 45694; 614-574-2385.

Hitachi V-509 oscilloscope, no substitute, can pay $600 if excellent. Marvin 0 Loftness, 115 West 20th, Olympia, WA 98501; 206-357-8336.

Leader oscilloscope LBO 301, working or non-working, in repairable condition. Mike Shelton, 2708 May Drive, Burlington, NC 27215; 919-227-290&

High-voltage transformer for MGA model CS1981 color set, need complete transformer; push-pull output transformers for the Leslie external speakers #10I and #102, were used with the Gulbransen theater organ, could use the whole amplifier if available, uses 8-7189 and 4-I2AU7 tubes. Bfrrth Hitchock, Tri-City 7V, Rt. 3 Box 186, Birch Tree, MO 65438; 314-292-3281.

4657N. Neeley, Decatur, IL 62526; 217-429-2675.

Horizontal hold oscillator coil, part #2829-003-0105, for a 13ohsei model TC-800 color TV (made by Samsung), new or used. Send price. John Augustine, Augustine's 7V/Radio Service, 530 N. Ninth St., Reading, PA 19604; 2I5-372-543&

V-U meter for an AKAI model M-8 reel-to-reel tape recorder. Paul Jones, 10595 Vista Wilk Drive, San Diego, Cl 92131.

Service literature or address where to obtain info on a model 146LB1 Playmate organ by Thomas Organ Co. Willard Riierbach, RR1 Box 89, Coopersburg, PA 18036; 215-346-7701.

Service manual for a Toshiba model V8030T VCR, maybe same as model V5530. Will copy and return or buy. John Reynolds, 1942 Sandalwood Lane, Fort Collins, CO 80526; 303-484-2715.

Schematic and instruction manual for Keithley model 130 digital multimeter. Will copy and return or pay for copy. Gerard O'Gara, II Crag Lane, Levittown, NY 11756; 516-731-4075.

B&K model 606 Dyna Jet and 707 tube testers. Charles T Huth, 229 Melmore St., Tiffin, OH 44883; 419-448-0007

PLL/programmer PC board for a Radio Shack Realistic Comp-I00 scanner monitor, part number G.E.-21B-5703. James W Strickland, 413 Lakewood St., Blytheville, AR 72315; 501-763-4147

Schematic (with board layout) for a Readers Digest model RDA-127 radio; schematic for a Philco model 81-121; schematic for a Yorx model K3654 tape player. Must be reasonable. Good photocopy OK. A. Edward Ruppel, 1207 Adams St., Saginaw, MI 48602.

Heathkit IM 5258 distortion analyzer; B&K 2040 signal generator; wow and flutter meter. Must be reasonable. Gil Foley, 6205 N. 59th Ave., Glen-dale, AZ 8.5301; 602-937-3241.

Sams Photofact service manuals; CB radios; auto radios, scanners. Greg Hingle, Rt. 2, Box 584, Port Sulphur, LA 70083; 504-564-2517

FOR SALE Sam's with file cabinets, #600 through #1864, $800. Mark Oliva, Oliva Audio-visual, Box 742, Milford, NE 68405; 402-761-3344.

Model VR 9800 (Sony SL 2000) portable Beta video recorder with color camera, excellent con-dition, $450 or best offer; Simpson white dot generator, working, $20; working Philco Predic-ta, best offer; repairable Zenith JR9030 VCR, $50. Joe Sanfilippo, Northern Technical SIC, P.O. Box 347-1935 N. Framing Road, Woodruff WI 5456&

Tektronix model 2445 portable scope, 150MHz, CRT readout, delayed sweep, quad-trace, two brand-new probes, very good condition, $1,600 or best offer; Fluke 77 DMM, excellent condi-tion, $100. Roberto Duran, 1231 Sherbourne Drive, Los Angeles, Cl 90035; 213-272-7289.

portable Z-meter 2-capacitor/inductor analyzer, $750 (cost $995). Like new, manuals, VA62 videotape, will ship in original cartons. Rob's Video Services, 3100 S. Georgia, Amarillo, 7X 79109; 806-352-6699.

Eico model HVP-5 HV voltage probe. $25; Eico model 584 battery tester. $15; Stancor P-6415 isola-tion transformer, $25; 10 years of Sylvania fac-tory service manuals; transistors, chips and fac-tory parts (never used) — send SASE for list. No reasonable offer refused. Raynham 71i, 803 Or-chard St., Raynham, MA 02767: 508-824-4269.

Heathkit color bar generator, $50; B&K 466 pix tube tester and rejuvenator with adapters. $175; Knight R/cap. tester, $30. M.E. Andrews Jr , Box 91, Ereter, RI 02822.

Used only once. new Fluke model 87, true rms ac, 41/2-digit mode, back-lit display, frequency. capacitance and many other features, $225 plus shipping. Stanley Todorvw, 8468 Belle Bluff Drive, Grand Blanc, MI 48439; 313-695-0271.

Sams Photofacts. #250 through #1000. all for $150. Jennings Hanson, 735 Clematis Road, Venice, FL 34293; 813-493-4159 or 813-497-0108.

Sams Photofacts, #1-840 and #1380-2600 (50% be-tween 840 and 1380), $1,500 plus shipping. Lee Schantz, Lee's 7V Service, 5330 Galena Drive, Colorado Springs, CO 80918; 719-598-0508.

Sencore VA48. $475; Powerite PR57, $350; CR70 Beam Builder. $900; Heathkit 2240 digital LC bridge, $150. All in excellent condition, includes manuals, leads and warranties. Robert Bell, Route 3, Bar 400, Toccoa, GA 30577; 404-886-4466.

EMC model 206 tube tester (circa 1946/1947), brand-new, never used, includes operating manual; RCA model WR89A marker generator and RCA model WR59C sweep generator, includes all schematics and operating instructions; RCA model WV97 Sr. Voltomyst with operating manual and schematic. Melvin C. Roppelt, 216 Meadowvale Road, Lutherville, MD 21093; 301-825-4874.

Sencore CA55 capacitor checker. $175; Heathkit 115235 yoke and flyback tester. $125. Eddie Bryant, 9809 Hilgert Drive, Cleveland. OH 44104; 216-721-9435.

Magazines from early 1960's to present — PF Reporter, ET/D, ES&T — make offer; 305 new name-brand radio and TV tubes; 105 Sams Photofact folder sets; one set of radio manuals (24 volumes) by Supreme Publications; servicing diagrams 1926-1969; TexFax manuals — volumes 103-115. SASE for a more complete list. Elmer). Alderman, Rt. 2, Box 139, Madison, NC 27025.

Owner relocating — service manuals (Sams, Quasar, Sharp. NAP); test equipment; tubes; parts inventory; merchandise inventory; office equip-ment; many miscellaneous items; van, building and property. Great hunting and fishing. Building adaptable to many uses. R.N. Yasko. Fremont TV, 407 E. Main St., Fremont, WI 54940: 414-446-2239.

On/Off volume control for Quasar chassis CTS-9591301. service WT5812NW. Jim Bundy,

Sencore VA62 Universal Analyzer with VC63 VCR test accessory, $3,000 (cost $3,990); Sencore LC75


Repair shop over-stocked on many parts, modules, manuals, etc., no tubes or junk. Sell or swap. Send

SASE for list. All-Tech Service, 22622 Lambert, Suite 303, Lake Forest, Cl 92630; 714-951-5502.

Sencore VA62 video analyzer, in box, with cables and manuals, like new, $1,995 (includes COD shipping). Charles TV, CG. Owens. Rt. 210 and Poplar Lane, Indian head, MD 20640; 301-743-3153.

Millen 90651 grid dip meter, $50; Gertsch-Singer FM-9 frequency deviation meter, $325; Sencore FE-20 multimeter, $25; Bell & Howell model 34 oscilloscope, $25; Eico I47A signal tracer, $15. Will consider trades. Bobby Lee Deck, 122 Fourth Ave. S., Algood, IN 38.501; 615-537-9543.

Cramer Halldorson I2-inch degaussing coil, $10; Heath IT 5230 CRT tester with sockets and manual, $85. Both in perfect condition. P Davis, P.O. Box 615, Manasquan, NJ 08736; 201-502-0961.

Used Drake 240A satellite receivers with down converter, VCII compatible. Excellent working condition. Little Ocmulgee Service, PO. Box 150, Railroad Ave., Alamo, G4 30411; in Georgia, 800-342-1290; outside Georgia, 912-568-7171. Ask for Roger. ext. 218

RETIRING, please send SASE for listing and prices. Frank N. Sachs, 6803 Navajo Drive, Baltimore, MD 21209; 301-484-3115.

Sencore SC6I in original shipping box, with manual and cables, $2,000; Sencore CG25 in original box, $90. Both in excellent condition. Add shipping. C. Johnson, 2384 Shadow Hill, River-side, Cl 92506; 714-684-5583.

Sams 800-1799. Make offer. Calvin Boddie. 660 E. Yucca St., Oxnard, Cl 93030; 805-486-1071 after 5 p.m..

Sencore SC6I, VA62, VC63, in original box with all manuals and cables, $3995. Bony Davis, Davis Electronics, Graham School Road, Gallipolis, OH 45631; 304-675-1667

Hewlett Packard model 410B VTVM, $95; Hewlett Packard model 130C oscilloscope, 500kHz bandpass, $195; Tektronix model RM504 oscilloscope, 450kHz bandpass, $165. Add $10 for insured UPS shipping. COD OK. Fred Jones, 407 Morningbird Court, Niceville, FL 32578; 904-678-1803.

Sams #1 to #2627 (12/88), complete TV set, $5,000 or best offer. Mary Rainey, PO. Box 160, Con-cordia, MO 64020; 816-463-2689.

Atari parts and factory service manuals, 2600, 5200, 600, 800, 1200 and more; Mattel factory service manuals and parts. Originally over $2,000, all for $750 or best offer. Bob Brudis. PO. Box 9022, Youngstown, OH 44512.

Factory service manuals for VCRs, TVs, cameras, etc.; factory parts. Bob Brudis, PO. Box 9022. Youngstown, OH 44512.

B&K I077B TV analyst with slides and manual. $135; Heath model IM18 VTVM with instruction manual, $35. Mr. Lurry, 6738 Amherst St., San Diego, Cl 92115; 619-462-7445.

Sencore VA62. VC63 and NT64, includes all cables, in original boxes, excellent condition, $2,995 or best offer. Hiryne's 711.3/2 Second Ave., PO. Box 81, Low Moor, IA 52757; 319-522-2456 after 4 p.m.

Sams Photofacts from #1 to #1000 complete. best offer; 1,000 receiving tubes. Send SASE for list. Brian Iibtowicz, RD 2, Thornhill Drive, New Cas-tle, PA 16101; 412-652-4591.

CK 3000 Sylvania test jig; B&K 1075 analyst and A 107 CRT analyzer; Yeats TV dolly; B&K tube tester; misc. triplers, modules and condensers; manuals — RCA and Zenith; ES&T Profax from start. Robert Rash, Custom TV 137 Sir Damas Drive, Riverside, Cl 92507; 714-686-2019.

All car radio parts, boxed, all new, dated back to Kaison and Packerd; radios in original boxes; 12V vibroter, boxed; old Ford antennas; old car radio manuals. Gorski TV. 134 Voorhess Corner Road, Flemington, NJ 08822; 201-782-5468. •

Classified Advertising rates in the Classified Section are $1.65 per word, per insertion, and must be accompanied by payment to insure publication.

Each initial or abbreviation counts as a full word.

Minimum classified charge $35.00.

For ads on which replies are sent to us for forwarding (blind ads), there is an additional charge of $40.00 per insertion to cover department number, processing of replies, and mailing costs.

Classified columns are not open to advertising of any pro-ducts regularly produced by manufacturers unless used and no longer owned by the manufacturer or distributor.

FOR SALE

VHS-VCR Repair Solutions Volumes I, II, Ill, IV. Each con-tains 150 symptoms and cures, cross reference chart, free assistance. Each $11.95, any two $19.95, any three $29.95 all $39.95. Eagle Electronics, 52953 Locks Lane, Granger, IN 46530. 01-89-TFN

TV/VCR TUFF TIPS listed by mfg. & model. Over 400 tips. $21.95. TV Tips only $11.95, VCR Tips only $13.95. VCR

CROSS-REFERENCE listing for electronically similar manufacturers, RCA, GE, Sylvania, Panasonic, Quasar, Magnavox, Philco, & J.C. Penney, $19.95. TVNCR FAILURE HISTORIES. Multiple cures for most problem areas. Send $7.95 with mfg. and model number. Money will be refunded with free sample if model is not on database. Add $1.50 postage and handling. TECH CURES. 4825 Fredericksburg Road, San Antonio, Texas 78229.12-88-TFN

SENCORE SC-61 SCOPE, 1 yr. old, 100MHz digital dual trace. One probe readout DC w/ts. peak to peak, frequen-cy, and Delta measurements. Eliminates graticule counting. Obsoletes conventional scopes. $1500 sacrifice, $3000 new. Call collect 611235-4735. 7-89-1t

TV TROUBLESHOOTING: Over 300 problems/solutions. Nothing old listed. $12.00, add $1.50 shipping. Refund if not satisfied. Jones Electronics, Box 702, Niceville, FL 32578. 6-89-TFN

REDUCED 75%, Diehl Mark V scanner $249, Diehl Mark III scanner $99. New, 2805 University Ave., Madison, Wis. 53705, 608-2314629, 608-2319741. 3-89-tfn

TV TOUGH DOGS: 300 symptoms and cures. Send $8.95 to DAVIS TV, 11772 Old Fashion Way. Garden Grove, CA 92640. 10-87-tfn

PHOTOFACTS: Folders under #1400, $4.00. Above 0400. $6.00. Sent same day first•class postpaid. Loeb, 414 Chestnut Lane, East Meadow. NY 11554. 6.89-3t

SERVICES

SPEAKER REPAIR. 4"-18" Speakers reconed. Cross-over parts. Orban Audio, 119 7th St. NW, North Canton, Ohio 44720, (216) 497-9932 6pm-9pm EST. 4-89-ftn

HELP WANTED

SOLID OPPORTUNITY in Northern California. Audio-Video Technicians and Managers. We are Northern California's leading retailer/servicer of prestigious home electronics. ser-vicing brands like Yamaha, Luxman, Mitsubishi, Denon, Hitachi, and many more, and we're looking for some good technicens and service managers to continue to grow with our company in this beautiful wine-country area. Current openings in Santa Rosa and Bay area. Call Pete Coleman at (707)546-2736, or send resume to Technical Department, 2340 Coddingtown Center, Santa Rosa, CA 95401. M & W ELECTRONICS, INC.

BUSINESS OPPORTUNITIES

BE YOUR OWN BOSS—AudioNideofTVRO sales and serv-ice Perfect small business for 1-2 man operation Profitable Colorado business Low overhead, owner can finance 303-867-3554 6-89-21

AUDIO-VIDEO SERVICE. Big-Ten university sports/culture, small town atmosphere. $60K and growing. Hessian Elec-tronics, 401 S. Gilbert Street, Iowa City, Iowa 52240. (319) 351-5290. 7-89-1t

A SMALL TOWN—BUSY SHOP. equipment & inventory, owner retiring, price negotiable. Box 488, Salmon, Id 83467. 208-756-2916. 7-89-1t

VCR SERVICE COMPANY in beautiful Monterey, CA. $40.000-$50,000 yearly sales. $25,000 in parts, equipment, furniture and fixtures. Using only 400 square feet of 2,200 square feet. Busy drive-by corner building. Lease/rent— Only $675/mo. for entire facility. Lots of room to expand at no extra rent cost. Illness forces give away sale price of only $39.500. Hurry! Won't last. 408-649-6036. 7-89-3!

TV SALES & SERVICE: Beautiful Northern Arizona. Retir-ing due to health. Loaded with lup to date test equipt. Huge inventory, Sams photofacts from year one. Also Sharp, Fisher, JVC. Sansui, Sanyo, Samsung, RCA. GE. etc. Same location 26 years. Priced to sell, $45,000. For more infor-mation 602/635-4352. 7-8-21

ELECTRONICS BUSINESS: very diverse, factory sys con-tracts, installations for major dealers, growing security dept., all equipment & truck included, $55,000. Northern N.J. 201-575-6217. 6-89-3t


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FREE CALL 1-800-331-9658 DANDY MFG. CO. /RANDALL ELECTRONICS

(918) 682-4286. 2323 Gibson SI.. Muskogee. OK 74403


"Tech's Guide To Pricing" updated new 5th edition a fra me work for setting rates that apply to 1.11-Tech pro-ducts a formula that guarantees SUCCESS'

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REPRINTS Interested in ordering article reprints out of this or another issue?* Reprints can be excel-lent learning tools for your technical staff and great marketing tools for your sales staff. Call or write Kelly Hawthorne at Intertec Publishing Corp., P.O. Box 12901, Overland Park, KS 66212; (913) 888-4664.

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Ad Index/Hotline

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Chicago Case Co 23

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Dandy Mfg. Co 60

ETA 55

Falcon Safety Products, Inc. 11

Fluke, John Mfg. Co., Inc. 5

Hitachi Sales Corp. of America 41

HMC-HUB Materials Company 45

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Leader Instrument Corp 3

Nesda 45, 53

Nutronix, Inc 49

Parts Express Intl., Inc 21

Prime Electronics 60

PTS Corp. 37

Sencore, Inc. IFC

Simpson Electric Co. 15

Sperry Tech, Inc. 60

Techni-Tool 51

Tektronix, Inc 8A-8B,9

Tentel 60

Tool Kit Specialists, Inc 49

Vaco Products 53

Viejo Publications 53

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Similciv bdinabgy KANSAS CITY, MISSOURI Greg Garrison, Sales Manager PO. Box 12901 Overland Park, KS 66212 Phone: (913) 888-4664 Fax: (913) 541-6697 Telex: 42-4156 INTERTEC OLPK

OXFORD, ENGLAND Nicholas McGeachin Roseleigh House, New Street Deddington, Oxford OX5 4SP Phone: (0869) 38794 Telefax: (0869) 38040 Telex* 837469 BES G

TOKYO, JAPAN Mashy Yoshikawa Orient Echo, Inc. 1101 Grand Maison Shimomiyabi-Cho, 2-18 Shinjuku-ku, Tokyo 162, Japan Tel: 03-235-5961 Telex: J-33376 MYORIENT

FREWVILLE, SOUTH AUSTRALIA John Williamson Hastwell, Williamson, Rep. Pty. Ltd. 109 Conyngham Street Frewville 5063 South Australia Phone: (08) 79 9522 Fax: 08 79 9735 Telex. AA87113 HANDM


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For your own reputation and in your customers' best interest

always insist on

GenuinMnit1 7----&manufactured Replacement Parts Reconditioned and Serviced for Reliability

by Zenith People as Knowledgeable and Dedicated as Those Who Made the Originals!

One of the easiest, fastest, and surest ways for you to preserve the pedigree and maintain the quality of the Zenith products you service is with genuine Zenith replace-ment parts.

And at no time is this more critical than when you replace the more sophisti-cated components like modules, tuners, channel selectors and sub-assemblies.

Your participating Zenith parts dis-tributor will supply you with a replace-ment remanufactured, reconditioned and serviced for reliability by Zenith people as dedicated and knowledgeable as those who made the original.

Equally important, the replacement module or sub-assembly you receive in ex-change from your Zenith parts distributor

will most likely incorporate any Zenith factory-made modifications in effect at the time of remanufacture.

And nowhere else but in a partici-pating Zenith parts distributor's Exchange Program can you get assurance that a replacement incorporates Zenith factory up-dates!

To learn the location of the Zenith R&R Exchange Counter in your area, write on your company letterhead and we will help you locate one that's nearby.

Risking an exchange for a Zenith replacement anywhere else doesn't make sense. Not when factory-fresh replacement modules and sub-assemblies are so readily available thru a Zenith parts distributor's Exchange Program! Write now!

7The ty govt. ,1,011711 qualit es in before the name goes on.*

Zenith Service, Parts & Accessories • 11000 Seymour Avenue, Franklin Park, Illinois 60131 • A Division of Zenith Electronics Corporation

Documents

THE MAGAZINE FOR CONSUMER ELECIRONICS SERVICING ... · ELEGT111311THE MAGAZINE FOR CONSUMER ELECIRONICS SERVICING PROFESSIONALS .0 Se c (-g & Te C rrology JULY 1989/$2 5C Servicing