Chapter 2. TROUBLESHOOTING

CHAPTER 2

TROUBLESHOOTING

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

W a r n i n g : When servicing the test set, be extremely careful not to contact the B+

v o l t a g e s (from -150 volts to +300 volts dc, and from -300 volts to +150 volts dc). With

a c power removed, high dc potentials may still be retained as charges on capacitors.

Before touching the exposed parts, be sure that these potentials are removed by shorting

t h e capacitors to ground. Be especially careful when checking the ac input circuits at

tieholder XF701 at the terminals of powerline filters FL703 through FL706, at terminal

b o a r d s TB701 through TB706, and at the terminals of POWER ON-OFF switch S710.

63. General Instructions

and probes, the tuning units, the main unit,

a n d the external transformer (para 62)

Troubleshooting at field and depot main-

when its use is required. The first step in

t e n a n c e level includes all the techniques

tracing trouble is to locate the faulty unit

o u t l i n e d for organizational maintenance

by the following methods:

a n d any special or additional techniques

(1) V i s u a l inspection. Visual inspec-

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

t i o n enables the repairman to lo-

f i e l d and depot maintenance procedures

cate faults without testing or meas-

a r e not complete in themselves, but sup-

u r i n g circuits. This inspection is

p l e m e n t the procedures described in TM

valuable to avoid additional damage

1 1 - 6 6 2 5 - 3 5 1 - 1 2 . The systematic trouble-

w h i c h might occur to components

shooting procedure, which begins with the

t h r o u g h improper servicing meth-

o p e r a t i o n a l and sectionalization checks

o d s , and also to forestall future

that can be performed at an organizational

f a i l u r es. The visual inspection

level, must be completed by means of

checks with the power off are given

s e c t i o n a l i z a t i o n , localization, and isola-

i n TM 11-6625-351-12. With the

tion techniques.

p o w e r on, visual inspection often

enables the repairman to locate

64. Organization of Troubleshooting

tubes with open filaments, and

Procedures

gassy tubes which give off a bluish-

a. General. The first step in servicing a

purple glow. All meter readings or

d e f e c t i v e test set is to sectionalize the

o t h e r visual signs should be ob-

served and an attempt made to sec-

f a u l t . Sectionalization means tracing the

t i o n a l i z e the fault to a particular

fault to a major component or circuit re-

sponsible for abnormal operation. The

unit.

second step is to localize the fault. Local-

(2) O p e r a t i o n a l tests. Operation a 1

t e s t s frequently indicate the gen-

ization means tracing the fault. to a defec-

e r a l location of trouble. In many

tive part responsible for the abnormal con-

i n s t a n c e s , the results of the tests

d i t i o n . Some faults, such as burned-out

resistors or rectifiers, and arcing or

will determine the exact nature of

shorted transformers, often can be located

the fault. The operational checklist

by sight, smell, and hearing. The majority

i n TM 11-6625-351-12 is a good

o f faults, however, must be localized by

o p e r a t i o n a l test.

c h e c k i n g voltages and resistances.

c. Localization. The tests listed below

will help to isolate the trouble. First local-

b . S e c t i o n a l i z a t i o n . The test set con-

sists of several units: the various antennas

ize the trouble to a single stage or circuit,