TM 9-4935-282-34
803D
SYMPTOM
PROBABLE CAUSE
REMEDY
Drift of the 500 volt DC re-
V102, V104, or V105 defective.
Check V102, V104, and V105 by replacement.
ference supply evidenced
by the continual need for
One of the sampling string
Locate faulty resistor by heating slightly with
resetting with the CAL-
resistors (R123, R124, R121)
a soldering iron held near the resistor while
BRATE control.
is changing value rapidly as
observing the 500 volt DC calibration.
the instrument warms up.
Drifting standard cell emf
Allow time for the standard cell to stabilize.
possibly caused by previous
Several hours should be sufficient.
shorting or inverting of the
cell. (803D and 803DR)
Cannot calibrate 500 volt
Excessive aging of V102.
Check V102 by replacement.
DC reference supply.
Meter cannot be brought
Out of calibration.
Recalibrate per paragraph 4-4b.
to zero with CALIBRATE
control.
One or more resistors in
Recalibrate per paragraph 4-4b and observe stabliity
500 volt DC sampling string
for 48 hours. If 500 volt DC reference supply remains
has shifted in value.
stable, replacement of resistor is unnecessary.
Standard cell emf has
Recalibrate instrument and observe stability of
shifted. (803D and 803DR)
reference supply. Replacement of the stand-
ard cell may be necessary.
Measurements are out of
A reference supply output range
If the trouble occurs in the 50 volt range, R324 has
tolerance on one range
resistor on the range resistor
shifted; in the 5 volt range, R325 or R327 has shifted,
other than the 500 volt range.
printed circuit board is out of
in the 0.5 volt range, R328 or R330 has shifted. It may
tolerance.
be possible to correct by recalibration. If not, replace
faulty resistor.
Measurements are out of
R320 or R321 has shifted in value.
It may be possible to correct all range voltages by
tolerances on all ranges
recalibration. If not, replace faulty resistor.
other than the 500 volt range.
Measurements are out of
One of the Kelvin-Varley divider
Measure the voltage drop across each Kelvin-Varley
tolerance on any range
resistors is out of toleratnce.
resistor with another John Fluke Differential Voltmeter.
when the Kelvin-Varley
Begin by setting RANGE switch to 500 volts and the
divider is dialed to any
voltage readout dials to 499.910. Reference to the
setting other than 499910.
schematic diagram will show that there should be 100, 10,
1, 0.1, and 0.01 volts respectively across each resistor
of the A, B, C, D, and E decades, except for the two
resistors of each decade that are paralleled by the
following decade. Across these two resistors, there
should be 50, 5, 0.5, and 0.05 volts, respectively.
Voltage measurements should be within 0.01% of each
other. Remember that if one resistor in a decade has
increased or decreased appreciably, the voltage drop
across all other resistors in the decade will be slightly
slightly affected also.
Instrument is out of
Resistors R306, R307, R308,
Check and replace faulty resistor.
specifications on all range.
R309, or R310 out of tolerance.
Figure 4-1. TROUBLESHOOTING (sheet 1 of 2)
(Figure 4-1 Sheet 1 of 2)
(Figure 4-1 Sheet 2 of 2)
4-2
