CHAPTER 6 GENERAL SUPPORT MAINTENANCE INSTRUCTIONS

TM 11-6625-542-14-1

CHAPTER 6

GENERAL SUPPORT MAINTENANCE INSTRUCTIONS

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

inspection alone, the repairman frequently may discover

NOTE

the trouble or determine the circuit in which the trouble

No direct support maintenance is authorized.

exists. This inspection is valuable in avoiding additional

damage which occurs through improper servicing

WARNING

methods and in forestalling future failures.

Voltages as high as 230 volts exist at various

(2) Operational test. The operational test will

points in the equipment.

Be careful when

usually indicate the general location of trouble and will

servicing the equipment, even when power has

help in determining the exact nature of the fault. An

been turned off as voltages may still be present

operational test is given in paragraph 6-5.

in the line power circuitry. Failure to comply may

(3) Troubleshooting procedure. The trouble

result in serious or fatal injury.

symptoms listed in this procedure (sec II) will aid greatly

6-1. General Instructions

in locating trouble.

Troubleshooting at general support includes all the

(4) Intermittents. In all these tests, the

techniques required to isolate a defective part. Section II

possibility of intermittent conditions should not be

presents detailed troubleshooting procedures to enable

overlooked. If present, this type of trouble often may be

the repairman to localize and isolate a defective

made to appear by tapping or jarring the equipment. It is

component.

possible that some external connections may cause the

6-2. Organization of Troubleshooting Procedures

trouble. Test wiring for loose connections and moves

a. General. The first step in servicing a defective

wires and components with an insulated tool, such as a

AN/USM-108A

sectionalize

the

fault.

pencil or fiber rod. This may show where a faulty

Sectionalization means tracing the fault to one of the

connection or component is located.

three major sections responsible for the abnormal

6-3. Test Equipment Required

operation: the power supply section, the oscillator

The items of test equipment required for troubleshooting

section, and the divider section. The second step is to

the AN/USM-108A are listed below. Technical manuals

localize the fault. Localization means tracing the fault to

associated with each item are also listed.

a particular stage or network within one of the three

Test equipment

Technical Manual

major circuits. The third step is to isolate the fault.

Voltmeter, Electronic

TM 11-6625-438-15

Isolation means tracing the fault to the defective part

AN/USM-98

responsible for the abnormal condition. Some faults,

Variable Transformer CN-

such as burned-out resistors, arcing, and shorted

16/A

transformers, often can be located by sight, smell, and

oscilloscope AN/USM-

TM11-6625-1703-15

hearing. The majority of faults, however, must be

281A

isolated by checking voltages and resistances.

53-ohmtermination

b. Component Sectionalization, Localization, and

connector

Isolation. Listed in (1) through (4) below is a group of

93-ohmtermination

tests arranged to simplify and to reduce unnecessary

connector

work and to aid in tracing a trouble to a specific

Digital Readout Elec-

TM 11-6625-700-10

component. Follow the procedure in the sequence

tronic Counter

given.

AN/USM-207

(1) Visual inspection. The purpose of visual

inspection is to locate any visible trouble. Through

6-1