TM 11-6625-486-14&P
Table 6-3. Troubleshooting
Malfunction
Probable Cause
Corrective Action
1.
Frequency meter operates normally
Fuse F701 or F702 blown.
Replace fuse.
on batteries, but not on ac power.
Ballast lamp DS703 open.
Check resistance (200 ohms) and
replace if necessary.
Wiring in power cable
Check continuity and repair.
Power switch S701B defective.
Replace switch.
Primary of T701 open.
Check resistance of primary winding
if necessary.
No power supply output voltage from
On power supply circuit board (fig.
secondary winding of T701.
FO-2 or FO-3) check dc voltage
from TP601 to ground. If indicated
voltage is not present, check ac
voltage between terminals 1-5 and
5-6 of board. If no ac voltage
exists, replace T701.
Resistor R601 open.
Replace R601.
Diode rectifier CR601 or CR602
Replace diode.
defective.
Secondary winding of T701 open.
On power supply circuit board
measure dc resistance between
terminals 5 and 6 and then between
5 and 1. If resistance differs ap-
preciably from 60 ohms, replace
T701.
2. Frequency meter operates normally
Battery power interlock switch S702
Remove battery drawer. Check
on ac power, but not on batteries.
not closing battery circuit.
continuity through switch and
replace S702 if necessary.
Function switch S701 not completing
Check continuity from terminal (black
circuit.
wire) of battery interlock switch
S702 to cathode side of CR603 (fig.
remove battery drawer and turn
FUNCTION SW to OPER. If
circuit is open, replace switch
DS701.
Switching diode CR603 defective.
If battery voltage is present at
junction of R604 and CR603 but
not on TP601, replace CR603.
3. Frequency meter operates normally
Voltmeter M701 multiplier resistor
Replace R604.
on batteries, but panel voltmeter
R604 open.
does not indicate.
Voltmeter M701 defective.
Replace M701.
4. Frequency meter operates normally
Voltage dropping resistor R605.
Replace R605.
on ac power, but panel voltmeter
Multiplier resistor R604.
Replace R604.
does not indicate.
Meter M701 defective.
Replace M701.
5. Frequency meter inoperative on
Capacitor C702 or C704 shorted.
Check voltages on TP601, TP602,
either batteries or ac power.
and TP603 (collector, base, and
emitter of Q601) (fig. FO-2 or FO-
3). Check forward and reverse
resistance at the above test points
If no voltage exists at TP601 and a
resistance measurement to ground
indicates only a few ohms, replace
capacitor C703 (fig. 6-1).
If a low resistance exists from TP603
to ground, replace capacitor C704.
Regulator Q601 base bias resistor
Check voltage on TP602 (base of
R602.
Q601) (fig. FO-2 or FO-3) and
replace R602 if necessary.
Zener diode Z601.
Check resistance from TP602 to
ground. If resistance is low, replace
Z601.
Regulator Q601.
Replace Q601.
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