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CHAPTER 2

FOURTH ECHELON MAINTENANCE

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

Warning: When servicing the TS-1777/VRM-1, be careful when working near power

connections. Injury may result from contact with these connections.

28. General Instructions

Troubleshooting of Test Set, Radio AN/

VRM-1 at the fourth echelon includes all

the techniques outlined for organizational

maintenance and additional techniques re-

quired to localize troubles to a particular

plug-in assembly board to isolate a de-

fective part on the front panel and the

selector switch. These fourth echelon pro-

cedures are not complete in themselves

but supplement the procedures described

in TM 11-6625-496- 12. The systematic

troubleshooting procedure, which begins

with the operational and equipment per-

formance checklists that can be performed

at the organizational level, must be com-

pletely by means of localizing and isolating

techniques. Paragraphs 31 through 34 pro-

vide localizing and isolating techniques for

use by fourth echelon personnel. Para-

graphs 35 through 40 provide detailed

repair instructions, and paragraphs 41 and

43 contain a procedure for the overall ad-

justment of the AN/VRM-l.

29. Organization of Troubleshooting

Procedures

a. General. The first step in servicing

a defective AN/VRM-l is to localize the

fault. Localization means tracing the fault

to a plug-in assembly board, the front

panel, or a cable. The second step is to

isolate the fault. Isolation means tracing

the fault to a defective part responsible

for the abnormal condition. Some faults,

such as burned-out resistors, can often be

located by sight or smell. The majority of

faults, however, must be isolated by check-

ing voltages or resistances.

b. Localization. The first step in finding

a trouble is to determine which assembly

or assemblies are at fault by the following

methods:

(1)

(2)

Visual inspection. The purpose of

visual inspection is to locate faults

without testing or measuring cir-

cuits. Cables, connectors, indi-

cator lamps, and the fuse should

be inspected and an attempt made to

localize the fault to a particular

assembly.

Operational tests. Operational

tests frequently indicate the gen-

eral location of trouble. In many

instances, the tests will help in

determining the exact nature of the

fault. The equipment performance

checklist (TM 11-6625-496-12) is

a good operational test.

Troubleshooting Chart. The trou-

ble symptoms listed in the chart

(para 33) will aid in localizing a

trouble to-an assembly or part.

(3)

c. Isolation. The tests listed below will

aid in isolating the trouble. After the trou-

ble has been localized to an assembly,

isolate the trouble within the assembly by

voltage, resistance, and continuity meas-

urements.

(1) Voltage and resistance measur-

ements. This equipment contains

transistors. Observe all precau-

tions to prevent damage to transis-

tors. Make voltage and resistance

measurements only as specified.

When measuring voltages, use tape

or sleeving to insulate the entire

test prod, except for the extreme

tip. A momentary short circuit

can ruin the transistor. Use the

resistor and capacitor color codes

(fig. 35 and 36) to find the value of

components.

Use the resistance

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