Section II. TROUBLESHOOTING - TM-11-6625-667-450148

TM 11-6625-667-45

stant current amplifier. Such action will effec-

regulator A3Q1 to increase or decrease its out-

tively change the on-off period of series power

put as applicable.

Section II. TROUBLESHOOTING

been sectionalized ( b above). Localization pro-

5.1-5. Organization of Troubleshooting

cedures applicable to this equipment are de-

Procedures

scribed in paragraph 5.1-7, and should be

a. General. The first step in servicing a

used to localize the trouble to a stage in the

test set with improper mode 4 operation is to

suspected module or subassembly.

sectionalize the fault. Sectionalizing means

d. Isolation. Procedures for isolating trou-

tracing the fault to either module Al, A2, or

ble to a detail part are given in paragraph 5.1-

A3. The second step is to localize the fault.

Localization means tracing the fault to a defec-

e. Techniques. The techniques for section-

tive stage or circuit causing the abnormal con-

alization are described in paragraph 5.16, and

dition. The third step is isolation. Isolation

those for isolation in paragraph 5.1-3. In per-

means locating the defective part or parts that

forming localization and isolation procedures,

are responsible for the malfunction.

one or more of the techniques described below

NOTE

may be applied. Apply these techniques only

The equipment must provide a satis-

as indicated and observe all cautions.

factory self test before proceeding

(1) Voltage measurements. This equip-

with mode 4 tests. A mode 4 self test

ment containes transistor circuits. When measur-

cannot be performed. In the event of

ing voltages, use tape or sleeving to insulate

a self test REJECT indication, refer

the entire test probe, except for the extreme

to troubleshooting instructions for

tip. A momentary short circuit can damage a

other test set operations.

transistor. Use the same or equivalent elec-

tronic multimeter specified on the voltaged

b. Sectionalization. To simplify the location

and resistance charts.

of a fault, it is convenient to consider that

there are six main functional mode 4 circuits:

NOTE

power supply, challenge video circuit, reply

Modules A1 and A2 contain digital

decoder, counter circuits, double-reply detec-

circuits. Do not attempt to analyze.

tion circuit, and reply evaluator; therefore, the

their operation with voltage readings.

first step in tracing troubles is to determine the

A n a l y z e their operation with the

circuit where the fault is location.

waveforms in figures 5.1-8 and 5.1-9.

(1) Visual inspection. The purpose of

(2) Resistance measurements. Make tran-

visual inspection is to locate faults that may be

sistor resistance measurements in this equip-

evident without testing or measuring. This in-

ment only as directed on the voltage and re-

cludes such things as broken wires, bent or

sistance diagrams. U s e only the ohmmeter

corroded connector pins, damaged

circuit

ranges indicated on figures 5.1-3, 5.1-4, and

boards, or loose RF jacks and plugs. All possi-

5.1-5; otherwise, the indications will not be

ble visible inspections should be performed

accurate.

before attempting operational tests.

(2) Sectionalization tests. The sectionli-

CAUTION

zation tests are operational type tests and fre-

Before using any ohmmeter to test

quently indicate the general location of trou-

t r a n s i s t o r s or t r a n s i s t o r circuits,

ble. In some instances, the tests will help in

check the open-circuit voltage across

determining the exact nature of the fault. Tests

the ohmmeter test leads. Do not use

are given in paragraph 5.1-6.

the ohmmeter if the open-circuit volt-

age exceeds 1.5 volts. Also, since the

c. Localizatiotion.

Localization

procedures

RX1 range usually connects the ohm-

should be performed after the trouble has

5.1-5

Change 1