Chapter 2. TROUBLESHOOTING - TM-11-6625-623-450011

C2, TM 11-6625-623-45

CHAPTER 2

TROUBLESHOOTING

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

Warning: When servicing the function test set, be careful when working with the 115-volt,

100-CPS, ac line voltage. Disconnect the power cable from the power source when making in-

ternal resistance measurements.

(2) Measurement chart. If no symptoms

21. General Instructions

are known, perform the checks given

Troubleshooting at general support and de-

in the measurement chart (para 2-4).

p o t maintenance level includes all the tech-

(3) Troubleshooting chart. The symp-

niques o u t l i n e d for organizational mainte-

toms and procedures listed in the

nance and any special or additional techniques

troubleshooting chart (para 2-5) will

r e q u i r e d to isolate a defective part. The gen-

aid in isolating the trouble to a spe-

e r a l support and depot maintenance proce-

cific circuit or component.

dures are not complete in themselves but sup-

(4) Intermittent troubles. In all test, the

p l e m e n t the maintenance and repair proce-

possibility of intermittent troubles

d u r e s described in TM 11662562312. The

If pres-

should not be overlooked.

s y s t e m a t i c troubleshooting procedure, which

ent, this type of trouble often may be

begins with the maintenance and repair proce-

made to appear by tapping or jarring

d u r e s that can be performed at an organiza-

the equipment. C h e c k the wiring

t i o n a l level, must be completed by additional

and cable connections.

localizing and isolating techniques.

c. Isolation. Once the faulty circuit or sec-

tion of the circuit is located, the faulty compo-

2-2. Organization of Troubleshooting

nent is located by voltage and/or resistance

Procedures

measurements. Use the voltage and resistance

diagram (fig. 2-4) to find normal readings,

a. General. The first procedure in servicing

and compare them with readings taken. Use

a defective function test set is to localize the

resistor and capacitor color codes (fig. 49 and

f a u l t . Localizing means tracing the fault to a

410) to find the value of components.

circuit. The second procedure is to isolate the

f a u l t . isolation means tracing the fault to a

defective part responsible for the abnormal

2-3. Test Equipment Required

condition.

The following test equipment is required

b. Localization. The first procedure in trac-

for troubleshooting the function test set:

ing trouble is to locate the circuit at fault by

a. Multimeter ME26B/U (multimeter),

the following methods:

TM 11662520012, or equivalent.

AN/USM-98

Electronic

b. Voltmeter,

(1) Visual inspection. The purpose of

(differential voltmeter), TM 11-6625-438

visual inspection is to locate faults

10, or equivalent.

without performing tests or measure-

c. Power Supply PP-351/U (dc power s u p -

ments. Some faults, such as burned-

ply), TM 115121, or equivalent.

out resistors, can be located by sight.

The trouble, therefore, can be im-

Voltage supply must be adjustable to two-deci-

Note.

mediately isolated.

mal place accuracy.