Table 4-1. Troubleshooting Chart.

TM 55-4920-325-14&P

whereas rotation of switch S402 causes an incor-

a. Input Power and Signal Voltages. If the

rect reading, then capacitors C403, C404, C405

test set is completely inoperative, check for input

and C406 are suspect and should be checked.

power (115 volts, 400 Hz) across J104-A and

J 104-C (see figure 4-9). Then check Power ON/

NOTE

OFF switch S101 and fuse F101. If signal voltage

Capacitors C401 through C411 are tem-

is not present across potentiometers R108, R109,

perature-stabilized assemblies. If a

or R120, check bridge transformer T101.

short or significant value change oc-

b. Switching Circuits. If operation of any test

curs, the defective capacitor assembly

set functional switch (S101 through S104, S401

must be replaced.

through S403) does not cause proper indication

d. Capacitance Indicator DSC686. If this unit

when the test set is operative, a power-off con-

is inoperative or cannot be properly calibrated, it

tinuity test may immediately locate the cause of

must be replaced. To check calibration, refer to

the trouble (refer to figure 4-9).

paragraph 2-6f. In addition, with pcwer off, use

c. Capacitance Simulator Assembly.

volt-ohmmeter and check for continuity between

Basically the capacitance simulator assembly con-

capacitance indicator case and the following pins

sists of capacitors C401 through C411, and rotary

of connector J101: J, I, M, and L. Resistance shall

switches S402 and S403 (see figure 4-9). If oper-

not be greater than 0.2 ohm.

ation of switches S402 and S403, or variable ca-

e. Megohmmeter Indicator DSM694. If this

pacitors C401 or C402 does not cause a related

unit is inoperative or cannot be properly cal-

indication on the CAPACITANCE INDICATOR, ei-

ibrated, it must be replaced. To check calibration,

ther replace the capacitance simulator assembly

refer to paragraph 2-8f. In addition, with power

as a unit, or isolate the trouble to the faulty com-

off, use volt-ohmmeter and check for continuity

ponent, replace and recalibrate. (See paragraph 2-

between indicator rear case plate and J501-N and

6f.) For example, if rotation of switch S402 causes

between J501-E and J501-L.

proper CAPACITANCE INDICATOR reading,

Table 4-1.

Troubleshooting Chart.

Malfunction

Probable cause

Corrective action

1. Test set completely

a. Fuse F101 open.

a. Replace fuse F101.

inoperative.

(Refer to para-

graphs 3-11 and

3-12.)

b. Power source faulty.

b. Use VTVM and

check input

power,

c. Faulty Power ON/

c. Replace switch

OFF switch S101

S101. (Refer to

(2, figure 2-l1.

paragraph 4-10.)

2. When measuring

a. Open in resistor net-

a.. Check and replace

capacitance, rota-

work R111 through

resistors as re-

tion of Capacitance

R114.

quired. (Refer

RANGE SELEC-

to paragraph

TOR switch S104

4-10.)

(7, figure 2-1)

b. Improperly calibrated

b, Check calibration

does not have

RANGE SELECTOR

as described in

proper effect on

switch

paragraph 2-6f.

CAPACITANCE

4-7