CHAPTER 4. MAINTENANCE

TM 55-4920-430-13

Chapter 4

MAINTENANCE

SECTION I TROUBLESHOOTING (CRC)

4-1. General Instructions.

a. Troubleshooting procedures are provided in logic tree format. Testing and troubleshooting are

correlated. For each test paragraph, there is a troubleshooting paragraph with a similar heading. For

each failure to meet a test requirement, there is a trouble symptom with a similar title. Use the

schematic diagrams (see FO-1, 1-3 through 1-12) and the wiring diagrams (see FO-55) as aids in trou-

bleshooting.

b. On wiring diagrams, wire connections to the moving contacts of rotary wafer switches stop at the

edge of the wafer. Physically, the moving contact is on the side of the wafer opposite the fixed contacts

and is centered between two fixed contacts. In troubleshooting logic, moving contacts are identified

with prefix W (wiper).

c. During troubleshooting, observe the following precautions and procedures.

(1) Voltage measurements. This equipment has transistor and microcircuits. When you measure

voltage, use tape or plastic sleeving (spaghetti) to insulate the entire test prod, except for the extreme

tip. A momentary short can ruin a transistor or microcircuit. Use the same or equivalent digital mul-

timeter specified in para 4-2.

(2) Resistance Measurements. Perform resistance and continuity checks with all electrical power

off.

(3) When the test set is disconnected from external test connections, all grounds in the test set are

not at the same potential. Chassis ground is at receptacle pin J7-B. Dc common, logic ground, and ac

signal ground are at TB1-3. Ac neutral is at TB2-7.

(4) Use a card extender, where necessary, for making test measurements at card receptacles.

4-2. Test Equipment Required.

TEST EQUIPMENT

SPECIFICATIONS

Function Generator

0 to 15 vac 90 phase shift

AC Power Supply, 400 Hz

0 to 115 vac

Oscilloscope

Dual trace, 0 to 100 mHz, 350 picosecond rise time

Digital Multimeter (2 ea)

50 mV to 150 vac 0.5%, 10 mV to 50 vdc 0.1%

Decade Capacitance Box

0.01 to 1.0 uf, 1.0 to 10.0 uf 0.1%

Decade Resistance Box

0.5 ohm to 1.1 megohms

Frequency Counter/Timer

1 Hz to 1 mHz

DC Power Supply 0-36V (2 ea)

0 to 36 vdc, 0.5%

Stop Watch

0.1 sec increments

Signal Test Aid

Local fabricated (fig. 4-10)

Resistance Test Aid

Local fabricated (fig. 4-10)

Card Extenders

Receptacle M55302/27-06 (60 pin)

to plug M55302/26-02

4-1