Testing Flybacks And Yokes With The RINGER Test

Flybacks (conventional and IHVT) and yokesoften develop shorted turns within their wind-ings. This type of failure is impossible to findwith any test other than the RINGER test. TheRINGER test provides an accurate, easy-to-use method of isolating these failures. TheRINGER test is included on many Sencoreinstruments. It approximates a “Q” test andworks by pulsing the coil and counting theresulting number of rings (oscillations) thatoccur before dampening to the 25 percentlevel.

A capacitor is placed in parallel with the coilfor impedance matching. The proper imped-ance is selected by rotating the IMPEDANCEMATCH switch to the position that producesthe maximum number of rings as shown onthe meter. (The LC77 and LC102 AUTO-ZMeters perform this impedance matchingautomatically.) If the highest readout is 10 orhigher, the coil or transformer has no shortedturns. If the coil has shorted turns, the read-ing will be less than 10. The RINGER test willindicate a BAD reading of less than 10 if thecoil has even one shorted turn.

How To Find Shorted Or OpenFlybacks With The RINGER Test

To test a flyback you need to make only oneset of lead connections to test all of thewindings. If none of the windings contain ashorted turn and if the winding you are con-nected to is not open, the RINGER test willread 10 or higher on at least one of thepositions of the IMPEDANCE MATCH switch.The “Z Meters” (other than the LC77 andLC102) have four switch positions, indicatedby a red band, that are used for testingflybacks and yokes. Use only these four po-sitions for testing yokes or flybacks. (Use allsix positions for testing coils other than yokesand flybacks.)

If any of the primary or secondary windingsof the flyback are shorted (even if the shortedwinding is electrically isolated from the oneyou are connected to), the magnetic energyaround the coil will be shorted out and theRINGER test will read less than 10 in all of theyoke and flyback positions of the IMPED-ANCE MATCH switch.

An open in the winding you are connected towill also produce a bad (less than 10) read-ing. If you suspect that a winding other thanthe one you are connected to is open (be-cause of the circuit symptoms), simply placea short across the suspected winding whileyou monitor the results on the winding youwere first connected to. The reading on theRINGER test will drop if the suspected wind-ing is good. The reading will not change if thewinding that you applied the short to is open.

To test a flyback:

1. Using a schematic, locate the windingconnected to the collector of the horizontaloutput transistor. Follow this winding to iden-tify the flyback lead that connects to the B+supply.

2. Connect one of the RINGER test leads tothe flyback lead that connects to the collectorof the output transistor. Connect the otherRINGER test lead to the flyback lead thatconnects to the B+ supply.

3. Push the RINGER test button, or turn theMETER switch to the RINGING TEST posi-tion, depending on which unit you are using.Rotate the IMPEDANCE MATCH switchthrough its yoke and flyback positions notingthe highest reading on the meter. If any of the

Fig. 1: Typical IHVT Circuit (RCA CTC108)

#116

#116#1

16

#1

16

#116

#116

ing will drop one count or less. If the flybackwas not shorted, the solder loop will nowcause the reading to drop significantly.

Test For Leakage Between Windings

Some flybacks may cause overcurrent shut-down in the chassis, yet test good with theRINGER test. The cause of this problem isusually leakage between different windingsin the flyback section of these flybacks, orleakage between a winding and the core ormounting bracket. Sometimes the windingshave a zero resistance short that can be foundwith an ohmmeter, but many times the leak-age only occurs when a higher voltage isapplied.

If the flyback passes the RINGER test but yoususpect possible leakage (the chassis drawsexcessive current, blows horizontal outputtransistors, or shuts down) check the flybackusing the LEAKAGE test found on one of theSencore Z Meters. The LEAKAGE test checksthe windings for breakdown with normalcircuit voltages applied. It will find leakagebetween separate windings, or leakage to thecore that goes unnoticed with other tests.Check leakage with both polarities of appliedvoltage by reversing the leads. This is neces-sary because the leakage path sometimesinvolves a diode which is only forward biasedby one polarity of applied voltage.

The leakage test must be performed with theflyback completely out of circuit. Set the ZMeter to its maximum Leakage Voltage set-ting, either 600 or 1000, depending upon themodel. The leakage between windings, andbetween each winding and the core shoulddrop to 0.0 m A. If any current is measured, theflyback should be replaced.

How To Ring Yokes

The tests of the deflection yoke are verysimilar to the flyback test. Test each of thefour yoke windings separately. The two ver-tical windings, for example, should both showthe same number of ringing cycles in thesame position of the IMPEDANCE MATCHswitch. If the yoke is open or has a shortedturn it will show a reading of less than 10. Ifit is not open or shorted it will show a readingof 10 or higher.

Each winding must be individually testedbecause a short in one of the yoke windingsis less likely to couple to the other windingsthan are the closely coupled windings of aflyback. Also, if two windings are in parallel,an open in one of the windings will not bedetected unless the two windings are testedseparately. Since there are only four wind-ings involved, however, this adds very littletime to the test.

readings is higher than 10, you know theprimary of the flyback is good, and none ofthe other windings are shorted.

4. If none of the positions of the IMPEDANCEMATCH switch reads higher than 10, isolatethe most likely loading circuits by discon-necting them in the following order : yoke,CRT filament (unplug socket), collector ofthe horizontal output transistor, and one endof the rectifier diode in each of the low-voltage supplies powered from the flyback.

After each circuit is disconnected, retest theflyback. If the flyback rings good after one ofthe loads is disconnected, the flyback is notshorted. Be sure to check the load that wasjust disconnected, however, for possible de-fects. (Note: In many cases these circuits,even if good, may normally cause the flybackto ring less than 10.)

5. If the flyback continues to test bad in thecircuit after disconnecting each of these loads,continue disconnecting the individual wind-ings. If the flyback still rings less than 10 inevery yoke and flyback switch position withall loads disconnected, it is bad and must bereplaced.

Tips on testing flybacks out of circuit:

1. Connect to the same flyback pins used forthe in-circuit test and perform the RINGERtest.

2. Do not lay the flyback on a metal surface,as the metal may affect the flyback in thesame way as a shorted turn.

3. The core and spacers must be in place totest the flyback. Without them, the flybackwill always test bad. If the replacement flybackcomes without the ferrite core and mountinghardware, be sure to remove them from thechassis and install them on the new flybackbefore performing the RINGER test.

A Final Tip For Absolute Confidence

If you ever have a doubt of whether a readingof less than 10 actually means that a flybackhas a shorted turn, there is a simple, addi-tional test you can perform to remove anydoubt. While ringing a flyback, wrap a turn ofsolder around the core and touch the ends ofthe solder loop together. If the flyback wasalready shorted, the shorted solder loop willhave very little additional affect and the read-

Fig. 2: Use the Z Meter LEAKAGE test to find shorts between flyback windings. Reverse the test leadsto check leakage with both polarities of applied voltage.

Fig. 3: The metal band surrounding many toroidal yokes causes the vertical windings to ring lower thannormal. A good vertical winding of this type rings 5 or higher.

Tips on testing yokes:

1. Whenever possible, test the yoke with itmounted on the CRT. Sometimes the pres-sure of the yoke mounting hardware causesa short. Removing the yoke relieves the pres-sure which may clear the short.

2. The damping resistors for the verticalwindings must be disconnected before doingthe RINGER test or they will cause the wind-ings to read bad, even if they are good.Sometimes the damping resistors are

3200 Sencore Drive, Sioux Falls, South Dakota 57107

For more information,Call Toll Free 1-800-SENCORE

(1-800-736-2673)

4. Do not test the yoke on a metal surface asthe metal may act like a shorted turn andcause all tests to show bad.

5. The horizontal yokes found in SCR-drivereceivers read only about 8 rings on theposition of the IMPEDANCE MATCH switchthat gives the highest reading.

6. Some toroidal yokes have a metal bandsurrounding their front perimeter, as shownin Figure 3. The metal band causes the yoketo appear as though it has a shorted verticalwinding when you perform the RINGER test.Instead of 10 rings, use 5 as the cutoff pointfor these vertical windings. A bad verticalwinding in this type of yoke will ring 0 or 1,while a good winding will ring 5 or higher.The RINGER test on the horizontal windingsin these toroidal yokes is not affected by themetal band.

mounted under the plastic terminal cover onthe yoke. In other sets they are on the chas-sis, and are disconnected when the yoke plugis disconnected.

3. If you must trace wires to determine whichconnectors are for which yoke coils, remem-ber that the vertical windings are located atthe sides of the yoke. The horizontal coils arelocated on the top and bottom of a conven-tional saddle yoke and are the toroidal wind-ings on toroidal-type yokes.

Form 4715Printed In U.S.A.

Notes:

#116

#116

#1

16

#1

16

#1

16

#1

16

#116

#116