CHAPTER 6 GENERAL SUPPORT MAINTENANCE

TM 11-6625-922-15

CHAPTER 6

GENERAL SUPPORT MAINTENANCE

Section I. GENERAL SUPPORT TROUBLESHOOTING

Warning.

When troubleshooting or making repairs in this equipment, be extremely careful. Voltages as

high as 230 volts ac and 250 volts dc are present internally when the unit has primary power

applied. Use insulated test probes when making voltage measurements. Always disconnect the

power cord from the source before touching any components mounted directly to the chassis, or

any part of the power supply. If only making measurements or tests on the printed circuit board

assemblies, the POWER switch need only be set to the OFF position before touching parts or

changing components.

disconnected from the unit, check the resistance or

6-1. General

continuity of any component suspected of being

a. The first step in troubleshooting the TS-

defective.

2669/GCM is to localize the fault. Localization means

tracing the fault to the defective circuit. For this

equipment, a fault must be localized to one of the circuit

6-3. Isolation Procedures

modules (para 5-7).

Caution:

b. The second step, isolation, means tracing the

This equipment contains transistors

fault to the defective part. Some parts, such as burned-

and diodes. Be extremely careful

out resistors or arcing or shorted transformers, can often

when measuring voltages to prevent

be isolated by sight, smell, or sound. The majority of

short circuits. Use tape or sleeving

faults, however, must be isolated by checking voltages

to insulate the entire test prod,

and resistances.

except for the extreme tip.

c. Standard repair procedures (TB SIG 222)

a. Perform isolation checks after trouble is

should be followed after a trouble has been isolated.

localized to a specific printed circuit board or

subassembly by the use of the foregoing procedures.

6-2. Localization Procedures

Use the schematic diagrams and the component

a. General. Familiarity with the overall operation

location drawings (figs. 9-3 to 9-33) to trace signals,

of the equipment (paras 5-4 and 5-5) and the detailed

measure voltages, monitor waveforms, and isolate

operation of each individual assembly (para 5-7) is

trouble to the faulty part.

important. Determine the equipment malfunction with

b. Semiconductors are a major cause of failure

the most probably faulty section, or trace the

than any other components.

Check to see that

malfunction back to its source. Use figure 9-35 showing

transistors are passing signals, and that the base and

typical wave-forms at key points on the modules, to help

emitter voltages are within approximately 1 volt of each

in the localizing trouble and in troubleshooting. The

other at all times. Check to see that the resistances of

location of all modules is shown in figure 9-34.

diodes are high in one direction and low in the other.

b. Power Supply. Check to see whether the power

Check to see that capacitors are not short-shorted or

supplies are furnishing the proper voltages under full

open, and that they will pass an ac signal. Replace any

load. The voltages should be within 3 percent of

component suspected of being defective with a good

nominal.

one, to verify localization of the fault.

c. Chassis Components. With the primary power

c. Use the extender board to facilitate localization.

See that all printed circuit boards are seated firmly in

their connectors for proper electrical contact. See that

all dc voltages and ground are applied to the board.

6-1