TM 11-6625-524-14-4
INOPERATIVE
a. Check the AC line power source for line voltage and frequency; it should
agree with that marked on the serial/power plate. Check the 3 wire grounded AC
l i n e power cord for continuity. C h e c k the line fuse for continuity and that it
a g r e e s with the ratings as factory specified. Use DC multimeter set to 1X ohms
p o s i t i o n for continuity checks.
b. I f the pilot light is illuminated but the voltmeter fails to respond to a
s i g n a l , verify the signal source's output.
c. Visually check the probe and probe termination for possible damage.
d. Try another measuring range to determine if the range being used is inopera-
tive.
e . Any further troubleshooting will require the removal of the voltmeter's
c a b i n e t . See paragraph 5-2.
f . Connect the voltmeter to a 115 volt, 60Hz power source. Set the POWER switch
to ON. Using the DC multimeter set to DC volts, check the power supply voltages and
compare to those as shown on the schematic diagram, figure F0-2.
g. Using the DC multimeter set to DC volts, check the amplifier board for DC
supply voltages and compare to those as shown on the schematic diagram, figure F0-1.
h. Disconnect DC multimeter; disconnect voltmeter from power source.
ERRACTIC OR INTERMITTEN
a.
Visually check the probe and probe termination for possible cause.
b.
Try another measuring range to determine if the range being used is inopera-
tive.
Any further checks will require the removal of the voltmeter's cabinet. See
d. With the cabinet removed, visually inspect for damaged circuit boards,
broken wires or loose mechanical parts.
e. Connect the voltmeter to a 115 volt, 60Hz power source. Set the POWER switch
to ON. Using the DC multimeter set to DC volts, check the power supply voltages and
compare to those as shown on the schematic diagram, figure F0-2.
f . Using the DC multimeter set to DC volts, c h e c k the amplifier board for
DC supply voltages and compare to those as shown on the schematic diagram, figure
9. Disconnect multimeter.
DC MODULATOR DRIVER
a. Verify the DC modulator driver's ( a 94Hz oscillator) output by measuring
the waveshape at the collector of 3Q2 with the oscilloscope and compare to the value
as shown on the schematic diagram, figure F0-1. I f the output is not within speci-
f i c a t i o n s , try substituting 3Q1 and 3Q2 with known good ones.
b. Check, and if necessary, set the oscillator's frequency to 94Hz by using
control 3R11.
c. D i s c o n n e c t oscilloscope.
POST AMPLIFIER, SYNCHRONOUS DEMODULATOR AND REFERENCE AMPLIFIER
The following procedure is used to check the overall performance of these stages:
a. With the voltmeter properly shielded (see paragraph 5-2) switch to the 0.01V
f u l l scale range.
b. Locate on the amplifier board link wire 3W3. Unsolder one (1) end of 3W3
from 3TP8 and with a short clip lead connect 3TP8 to 3TP10. With another short
clip lead connect 3TP13 to 3TP3.
