Chapter 2. TROUBLESHOOTING

TM 11-6625-1702-35

CHAPTER 2

TROUBLESHOOTING

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

bles in the test set to a particular component

Warning: Be careful when working on the

are listed in paragraph 27.

1 1 5 - v o l t ac line connections. DEATH or

d. Techniques. I n p e r f o r m i n g l o c a l i z a t i o n

SERIOUS INJURY may result from contact

and isolation procedures, one or more of the

with these terminals.

t e c h n i q u e s described below may be applied.

2-1. General Instructions

Use the techniques only as indicated, and ob-

Troubleshooting at the direct support, gen-

serve all cautions.

eral support, and depot maintenance categories

(1) V o l t a g e m e a s u r e m e n t s . T h i s e q u i p -

includes all the techniques outlined for organi-

ment is transistorized. When measuring volt-

zational maintenance and any special or addi-

a g e s , use tape or sleeving (spaghetti) to in-

tional techniques required to isolate a defective

sulate the entire test prod, except for the ex-

part. Paragraphs 2-4 through 27 describe

treme tip. A momentary short circuit can ruin

intraunit (within the unit) localizing and iso-

a transistor. Use Multimeter ME-26D/U.

lating procedures to be used at the direct sup-

(2) Resistance measurements. R e s i s t a n c e

port maintenance category.

measurements are used to perform continuity

2-2. Organization of Troubleshooting

c h e c k s as well as to measure the resistance

Procedures

o f a circuit or component. Be careful when

a. General. The first procedure in servicing

checking transistors.

the test set is to localize the fault. Localiza-

(3) Waveshapes. Compare the waveshape

t i o n means tracing the fault to a defective

obtained at an indicated point with that shown

stage or circuit responsible for the abnormal

in figure 44.

c o n d i t i o n . The second procedure is isolation

(4) Intermittent troubles. In all the tests,

which means finding the defective part or

the possibility of intermittent troubles should

p a r t s . Some defective parts, such as burned

not be overlooked. If present, this type of

r e s i s t o r s and arching shorted transformers,

trouble often may be made to appear by

can often be located by sight, smell, and

tapping or jarring the equipment. Make a

hearing. Most defective parts, however, must

v i s u a l inspection of the wiring and connec-

be isolated by checking voltages and resistance.

tions to the units of the test set. Minute cracks

b. Localization. Test set malfunctions are

in the printed circuit board can cause inter-

localized by using the troubleshooting chart in

mittent operation. A magnifying glass is often

p a r a g r a p h 25c. T h i s c h a r t l i s t s c o m m o n

helpful in locating defects in the printed circuit

trouble symptoms and provides corrective

board.

measures. Since the chart cannot list all trouble

symptoms that may appear, it should be used

(5) R e s i s t o r a n d c a p a c i t o r c o l o r c o d e

as a guide for analyzing symptoms that are

d i a g r a m s . Color code diagrams for resistors

not listed.

and capacitors (figs. 51 and 52 ) are provided

c. Isolation. Procedures for isolating trou-

to aid maintenance personnel in determining

2-1

Change 3