Section II. TROUBLESHOOTING PROCEDURES

TM 11-6625-542-14-1

Section II. TROUBLESHOOTING PROCEDURES

6-4. Preliminary Setup

Table 6-1. Waveshapes

a. Determine power source to be used and

connect power cable to rear of the AN/USM-108A and to

power source. If other than 117 vac power is to be used,

refer to paragraph 2-4 for rewiring of the power

transformer.

b. Set POWER ON switch to ON and check to

see that POWER ON indicator and CRYSTAL HEATER

indicator illuminate.

c. Allow equipment to warmup for a minimum of

15 minutes prior to testing.

CAUTION

This is a precision electronic test instrument. As

such, it includes factory adjusted controls and

specially processed vacuum tube. Unnecessary

tube replacement may degrade the performance

of the unit. When testing vacuum tubes, replace

all good tubes in their original sockets.

6-5. Operational Test

(table 6-1)

a. Microseconds Circuits.

(1) Connect oscilloscope to MARKER OUT

connector (refer to section IV for test equipment setup).

(2) Check to see that proper waveshapes and

time marks are obtained when MICROSECONDS

pushbuttons are depressed.

b. Milliseconds Circuits. Connect oscilloscope to

MARKER OUT connector and check to see that proper

waveshapes and time marks are obtained when

6-6. Sectionalization Testing

MILLISECONDS pushbuttons are depressed.

The following procedure describes methods by which

c. Second Circuits.

Connect oscilloscope to

troubles may be traced to a particular section. When

MARKER OUT connector and check to see that proper

troubleshooting the AN/USM-108A, investigate the power

waveshapes and time marks are obtained when

supply section first, because all other sections are

SECONDS pushbuttons are depressed.

dependent upon it.

d. Trigger Rate Circuits. Connect oscilloscope to

a. Power Supply.

TRIGGER OUT connector and check to see that proper

(1) Check to see that ac power is connected.

waveshapes and time marks are obtained when

(2) With POWER ON switch in the ON

TRIGGER RATE pushbuttons are depressed.

position, indicator lamp should be lighted and cooling fan

operating. Check fuse F101 if necessary.

(3) Take a voltage measurement check at the

6-2