© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-1 Electronics Principles & Applications Eighth Edition Chapter 10 Troubleshooting

© 2013 The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill

10-1

ElectronicsElectronics

Principles & ApplicationsPrinciples & ApplicationsEighth EditionEighth Edition

Chapter 10Troubleshooting(student version)

Charles A. Schuler

©2013


10-2

• Preliminary Checks• No Output• Reduced Output• Intermittents• Operational Amplifiers• Automated Testing

INTRODUCTION


10-3

Dear Student:

This presentation is arranged in segments. Each segmentis preceded by a Concept Preview slide and is followed by aConcept Review slide. When you reach a Concept Reviewslide, you can return to the beginning of that segment byclicking on the Repeat Segment button. This will allow youto view that segment again, if you want to.


10-4

Concept Preview• Observation, analysis and limiting the possibilities

are the key elements of troubleshooting.• The troubleshooting process should begin with a

system point of view.• Software problems can produce symptoms that act

like hardware failures.• Component level troubleshooting is based on

circuit laws.• Electrostatic discharge can damage or destroy

solid state components.


10-5

GOAL• Good troubleshooting

• Observe the symptoms

• Analyze the possible causes

• Limit the possibilities


10-6A System Point of View

Inputs

Network

Other hardware

Software

Power?

Controls

Connectors

Symptoms?

Diagnostics

* adjust framostat

* synthesizer off

* buy low* sell high

Causes?Components


10-7

Don’t forget to check for blown fuses!


10-8

RLOAD

SYMPTOMS

VLOAD = 0

VLOAD < NORMAL

VLOAD > NORMAL

FAULTS

ZENER OPEN

ZENER SHORTED

R1 OPEN

R1 > NORMAL

C SHORTED

VIN < NORMAL

R1

VIN

VIN = 0

C

ILOAD > NORMAL

C OPENVLOAD SHOWS NOISE


10-9

Electrostatic Discharge (ESD)


10-10

ESD

• device packaging• minimize device handling• minimize motion• use a wrist strap• stand on ESD work mat• use ESD work surface• touch ground first• ionized air• instrument grounding• follow procedures

PREVENTION


10-11

G.O.A.L. quiz

The key words in troubleshooting are observe,analyze and ________. limit

Symptoms must be analyzed from the__________ point of view. system

With computer based systems, a fault can becaused by hardware or _________. software

Some solid-state devices are easily damagedby ____________ discharge. electrostatic

Technicians sometimes wear a wrist strapto prevent _________. ESD


10-12

Concept Review• Observation, analysis and limiting the possibilities

are the key elements of troubleshooting.• The troubleshooting process should begin with a

system point of view.• Software problems can produce symptoms that act

like hardware failures.• Component level troubleshooting is based on

circuit laws.• Electrostatic discharge can damage or destroy

solid state components.

Repeat Segment


10-13

Concept Preview• Analysis by signal injection starts at the beginning

of the signal chain.• Analysis by signal tracing starts at the end of the

signal chain.• Signal generators and oscilloscopes are commonly

used for both of the above methods.• In-circuit testing with an ohmmeter can be

misleading due to multiple paths.• Signal comparison is handy when a working

channel or circuit is available.


10-14

SIGNAL INJECTION METHOD

STAGE 1 STAGE 2 STAGE 3 STAGE 4

SIGNAL GENERATOR


10-15

SIGNAL INJECTION METHOD(another approach)


SIGNAL GENERATOR

Some technicians prefer the “divide

and conquer” approach as it

often saves time.

Start in the middle.


10-16

SIGNAL TRACING METHOD (Divide and conquer works here too.)



10-17

0

V

mA EB

C

R1

In-circuit ohmmeter testing can be misleading.

Additional paths causethe reading to be low.


10-18

SIGNAL COMPARISON METHOD(Divide and conquer works here too.)

RIGHTSTAGE 1

RIGHTSTAGE 2

RIGHTSTAGE 3

RIGHTSTAGE 4

LEFTSTAGE 1

LEFTSTAGE 2

LEFTSTAGE 3

LEFTSTAGE 4


10-19

Concept Review• Analysis by signal injection starts at the beginning

of the signal chain.• Analysis by signal tracing starts at the end of the

signal chain.• Signal generators and oscilloscopes are commonly

used for both of the above methods.• In-circuit testing with an ohmmeter can be

misleading due to multiple paths.• Signal comparison is handy when a working

channel or circuit is available.

Repeat Segment


10-20

Concept Preview• Open capacitors do not usually cause dc voltage

errors.• An open emitter bypass capacitor will cause the

voltage gain to be abnormally low.• An open coupling capacitor will break the signal

chain.• Shorted capacitors usually do cause dc voltage

errors.• Open resistors usually do cause dc voltage errors.• An open resistor can cause an amplifier to operate

in saturation or cutoff.


10-21

If any of these are open, there are no dc voltage errors.

Open causes decrease in gain

Open causes loss of signal

Open might cause hum or noise


10-22

If any of these are shorted, there are dc errors.

Short causes increase in

transistor current

Short causes loss of B-E biasand transistor is cutoff

(depends on prior stage)

Short causes amplifier voltages to be zero


10-23

This instrument will find several kinds of faults. For capacitors, it can determine shorts, opens, and high series resistance (which can cause bypass capacitors to not do their job).


10-24

If this is open,the amplifier

voltages are 0.


10-25

If either ofthese is open,the transistor

is in cutoff.

Which of these two faults will produce a non-zero emitter voltage?


10-26

If this is open,the transistorapproachessaturation.

Will the collector voltage be high or low?


10-27

If this is open,the transistorcollector goesto zero volts.

Will the base voltage be off very far?


10-28

Component level troubleshooting quiz

Ohmmeter troubleshooting can be misleadingwhen performed _____ a circuit. in

Dc voltage errors are usually not caused by_________ coupling capacitors. open

A shorted coupling capacitor could cause theQ-point to move to cutoff or ______. saturation

When a base bias resistor opens, the Q-point__________ changes. always

Stage-by-stage verification with an oscilloscopeis called signal ____________. tracing


10-29

Concept Review• Open capacitors do not usually cause dc voltage

errors.• An open emitter bypass capacitor will cause the

voltage gain to be abnormally low.• An open coupling capacitor will break the signal

chain.• Shorted capacitors usually do cause dc voltage

errors.• Open resistors usually do cause dc voltage errors.• An open resistor can cause an amplifier to operate

in saturation or cutoff.

Repeat Segment


10-30

Concept Preview• A dummy load should be used when verifying

power output.• Triangle waves make it easy to recognize signal

distortion.• Intermittents might appear with changes in supply

voltage, with temperature, or with vibration.• When an op amp output goes to its maximum

negative or positive value it is “at the rail.”• When an op amp is at the rail, there could be an

open resistor, a resistor out of tolerance, or a bad supply voltage.


10-31

VERIFYING POWER OUTPUT

SIGNAL GENERATOR

DUMMYLOAD

AMPLIFIER


10-32

CHECKING FOR DISTORTION

TRIANGLE GENERATOR

AMPLIFIER

Crossover

Clipping


10-33

Making intermittents show up

• System view (Is any software involved?)

• Wiggle it

• Thump it (don’t get carried away)

• Heat it (don’t melt anything)

• Cool it

• Raise supply voltage (moderate amount)

• Lower supply voltage


10-34

- 5 V

5 k

Here’s a solution: add a negative voltageto cancel the positive dc offset of the source.

100 k

1 k

1 VDC

1 k

RL

Suppose a signal source has a dc component that must beeliminated but a coupling capacitor is not acceptable.


10-35

100 k

1 k

1 VDC

1 k

RL

Suppose the output voltage is at negative saturation.

- 5 V

5 k

- 12 V

Could the 5 kresistor be open?Could the - 5 V supply be at fault?

What else could be wrong?


10-36

Verification and intermittent quiz

Amplifier power output is best measuredusing a ________ load. dummy

The waveform that makes it easy to seeamplifier distortion is the _______. triangle

Intermittents caused by poor connections maybe located by using __________. vibration

Some intermittents can be made to appear bychanging temperature or supply _____. voltage

When an op amp shows dc output error, checkfirst for dc _________ error. input


10-37

Concept Review• A dummy load should be used when verifying

power output.• Triangle waves make it easy to recognize signal

distortion.• Intermittents might appear with changes in supply

voltage, with temperature, or with vibration.• When an op amp output goes to its maximum

negative or positive value it is “at the rail.”• When an op amp is at the rail, there could be an

open resistor, a resistor out of tolerance, or a bad supply voltage.

Repeat Segment


10-38

Concept Preview• Boundary scan was developed to replace the bed

of nails manufacturing test procedure.• Boundary scan can also be used for field service

work.• Scan cells support both normal operation and

diagnostic modes which can verify inputs and outputs, test circuit board traces, and check device functions.

• Boundary scan devices have at least four extra pins: test data in, test data out, test mode select, and clock.


10-39

Test data in

Test data out

Virtualnails

During a scan,devices can be

checked forproper function.

During a scan,I/O ports can be


During a scan,circuit traces can be


Boundary scan functions

Scanchain


10-40

More boundary scan functions


10-41

Each boundary scan chip pin is connected to cell.

Scan chain

Core

CellNormal output

Serial output

Serial input

Normal input(from core)

When the normal input is routed tothe normal output, the chip worksas if there was no scan function.

The normal output can bedriven by the serial input.The serial output can be

driven by the serial input.


10-42

SN

74B

CT

244

SN

74B

CT

8244

A

Octal buffer/driver

Test data out Test data in

Test clockTest mode select

Boundary scan version


10-43

Analog boundary scan


10-44

Concept Review• Boundary scan was developed to replace the bed

of nails manufacturing test procedure.• Boundary scan can also be used for field service

work.• Scan cells support both normal operation and

diagnostic modes which can verify inputs and outputs, test circuit board traces, and check device functions.

• Boundary scan devices have at least four extra pins: test data in, test data out, test mode select, and clock.

Repeat Segment


10-45

• Preliminary Checks• No Output• Reduced Output• Intermittents• Operational Amplifiers• Automated Testing

REVIEW

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© 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 10-1 Electronics Principles & Applications Eighth Edition Chapter 10 Troubleshooting