Voltage and Resistance Measurements - TM-11-6625-601-340030

TM 11-6625-601-34

be used in localizing the trouble to a functional

CAUTIONS

circuit in the suspected unit.

1. This equipment contains transis-

The

(1) O p e r a t i o n a l t e s t p r o c e d u r e .

tor circuits in both the test set and

procedures (TM

monthly

maintenance

simulator. Be sure that the test equip-

ment used is equipped with polarized

11-6625-601-12), in some cases, localize a trou-

ground plugs. If substitute test equip-

b l e to a specific circuit in the test set or

ment is used that does not have an iso-

simulator.

lation transformer in its power supply

(2) Radio Set AN/ARC-54 test procedure. A

circuit, connect one in the input power

complete AN/ARC-54 Radio Set known to be in

circuit. (A suitable transformer is iden-

good operating condition is part of the test

tified by Federal stock number

equipment r e q u i r e d a t t h e d i r e c t s u p p o r t

5950-356-1779.)

m a i n t e n a n c e level. T o l o c a l i z e a t r o u b l e

2. Make test equipment connections

detected while performing the AN/ARC-54 test

with care so that shorts will not be

procedures, the repairman may duplicate the

caused by exposed test equipment con-

test wherein the fault occurred and, by use of

nectors. Tape or sleeves (spaghetti) test

schematic diagrams, v o l t a g e and resistance

prods or clips as necessary to leave as

charts, will localize a trouble to a functional cir-

little exposed as needed to make con-

cuit.

tact to the circuit under test.

NOTE

2-4. Voltage and Resistance Measurements

If none of the AN/ARC-54 test proce-

Normal voltage and resistance measurements

dures can be performed, there is a pos-

taken at the base, collector, and emitter of the

sibility that no power is being applied

audio amplifiers in the test set and simulator

AN/ARC-54

unit

the

are presented in the tables in paragraph 2-5.

( R T - 3 4 8 / A R C - 5 4 , C-3835/ARC-54, or

C U - 9 4 2 / A R C - 5 4 or CU-943/ARC-54)

CAUTION

under test. Refer to the power routing

When measuring voltages, use tape or

diagram (fig. FO-6) and make voltage

s l e e v i n g (spaghetti) to insulate the

checks at the appropriate pins on the

entire test prod, except for the extreme

unit connector.

tip. A momentary short circuit can ruin

a transistor.

d. Isolation. Once a trouble has been localized

a. Voltage Measurements. The voltage read-

to a functional circuit in the test set or

ings in the tables (para. 2-5) were obtained

simulator, f u r t h e r tests and measurements

under the conditions specified in (1) and (2)

must be made to isolate the trouble to a compo-

b e l o w . Always make voltage measurements

nent part. The most useful tool that a technician

under these same conditions, or the readings

has for troubleshooting any circuit is his com-

obtained may be inaccurate. Make all voltage

plete understanding of the circuit operation.

measurements with a vtvm that has an input

When a trouble has been localized to a func-

impedance of at least 10 megohms (Voltmeter,

tional circuit, refer to chapter 1 and review the

Meter ME-30A/U, or equivalent). Connect the

principles of operation of the circuit. Chapter 1

dc common clip or the ac ground clip of the vtvm

contains functional and simplified schematic

to chassis ground of the unit under test.

diagrams of each test circuit. These schematic

for

audio

(1) Voltage

measurements

diagrams omit the components and switches

a m p l i f i e r card A1 (part of Test Set, Radio

that are not directly involved with the circuit.

TS-1967/ARC-54).

These diagrams make the circuit more easily

(a) Connect a 1 0 - o h m (-watt, 10-

understood than does the overall schematic

p e r c e n t ) resistor between pins 2 and 4 of

diagram. Parts locations are indicated in figures

HEADSET jack J9.

2-1 through 29. The voltage and resistance

(b) Connect a 150-ohm (-watt, 10-

tables (para 25) are valuable aids in isolating a

p e r c e n t ) resistor between pins 5 and 6 of

defective component. When making resistance

measurements, refer to figures FO-7, FO-8, and

RCVR/XMTR jack J11.

figures 2-14 through 222 as needed. Color code

(c) Apply +27.5 volts dc 1 to POWER

jack J32.

diagram for coils, resistors, and capacitors (fig.

(d) Set the POWER circuit breaker to ON.

FO1), provides pertinent resistance, voltage

(e) S e t TEST FUNCTION SELECTOR

rating, and tolerance information.

2-2