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 TM 11-6625-537-14-1
Table 6-1. Troubleshooting-Continued
Probable cause
Corrective action
Malfunction
Check wiring for shorts and loose
connections. Power transformer
winding dc resistance data is
given in figure 6-1.
Tube
Pins
Viol
4,5
4,5,9
V105
V202
4,5
V203
4,5
V501
4
V502
4
a. Check V102, V104, and V105 by
a. V102, V104, or V105 faulty.
2. Calibrate control must be
replacement. Some output voltage
continually reset: 500 volt dc
drift may be noted when replacing
reference supply is drifting.
V104 or V105. This drift will
normally disappear after the tube
has aged a bit. When replacing
V 102, use a type OG3 tube which
has been aged for at least 150
hours, to obtain stable operation,
b. One of the sampling string
by heating slightly with a warm
resistors ( R123, R124) is changing
soldering iron held near the
valve rapidly as the electronic
resistor.
Hold OPERATE-
voltmeter warms up,
CALIBRATE
switch
at
CALIBRATE
and observe
VOLTS meter indication while
heating resistor. Replace faulty
resistor.
a . Out of calibration........
a. Refer to depot maintenance
3. VOLTS meter cannot be nulled by
personnel.
adjusting CALIBRATE control
while OPERATE-CALIBRATE
b. Observe stability by periodically
b. One of the sampling string
switch is held at CALIBRATE.
setting OPERATE-CALIBRATE
resistors (R123, R124, or R121)
switch to CALIBRATE and
has shifted in value.
noting VOLTS meter deflection.
Replacement of resistor is not
necessary if 500-volt dc reference
supply remains stable.
Check V 102 by replacement. Use a
4. VOLTS meter cannot be nulled
Excessive aging of V 102
type OG3 tube which has been
by adjusting 500 VDC ADJ R121
aged at least 150 hours.
(fig. 6.7) during calibration.
Replace faulty resistor (fig. 6-8),
5. Differential measurements are out
A resistor on the reference range
Range
of tolerance on one dc range other
Resistor
divider printed circuit board is
50
than the 500-volt range,
out of tolerance.
R324
5
R325 or R327
.5
R328 or R330
Replace faulty resistor.
R320 or R321 has shifted in value
6. Measurements are out of tolerance
on all ac ranges and on the 50-,
5-, and .5-volt dc ranges.
Perform precision voltage divider
7. Measurements are out of tolerance
One of the resistors in the precision
fault isolation {para 6-8).
on any range when voltage
voltage divider is out of tolerance,
readout dialas are set to any
position other than 49 99&
0. Voltmeter is out of specification on
a. Refer to depot maintenance
all vtvm ranges.
personnel.
b. Check and replace faulty resistor,
b. Faulty resistor in null and range
divider string (R301 through
R31O).
9. VOLTS meter cannot be eat for
a. Moisture or dirt on printed circuit
a. Clean instrument (para 4-6).
zero deflection by adjusting
boards or switches.
VTVM ZERO ADJ R227.
b. Locate faulty component by
b. Faulty component
performing voltage and resistance
measurements on terminals of
V202 and V203. See figure FO-5
for nominal values.
6-3
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