TM 9-4935-282-34
803D
SYMPTOM
PROBABLE CAUSE
REMEDY
Meter rattle, drift, or
V202, V203, or V204 faulty.
Check V202, V203, and V204 by replacement.
error is observed on all
null ranges.
Chopper G1 faulty.
Replace chopper.
Moisture or dirt on printed
Clean instrument.
circuit boards or switches.
NOTE: Assuming all DC measurements are normal, the following symptoms are common to AC measurements only.
Measurements are out of
Out of calibration.
Recalibrate per paragraph 4-4c.
tolerance on 500 volt AC
range only.
One or more resistors
Recalibrate per paragraph 4-4c. Recheck calibration after 48
in 500 volt AC attenuator has
hours and if attenuator has remained stable, replacement
shifted in value.
of resistor is unnecessary. If attenuator does not remain
stable, or calibration is not possible, replace
faulty resistor.
Measurements are out of
Out of calibration.
Recalibrate per paragraph 4-4c.
tolerance on 50 volt AC
range only.
One or more resistors in
Recalibrate per paragraph 4-4c. Recheck after
50 volt AC attenuator has
48 hours and if attenuator has remained stable,
shifted in value.
replacement of resistor is unnecessary. If
attenuator does not remain stable or if calibra-
tion is not possible, replace faulty resistor.
Measurements out of toler-
Out of calibration.
Recalibrate per paragraph 4-4c.
ance on all AC rages.
V501 or V502 faulty.
Check V501 and V502 by replacement.
Measurements out of
Out of calibration.
Recalibrate per paragraph 4-4c.
tolerance at a specific
Faulty frequency compensa-
Locate faulty capacitor and replace. If trouble occurs on all
tion capacitor.
ranges, check C504. If trouble occurs on 500 volt range
only, check C501, C502, and C521. If trouble occurs on 50 volt
range only, check C523 and C524. If trouble occurs on 500, 50,
and 5 volt range, check C520. If trouble occurs on 0.5 volt
range check C519.
Figure 4-1. TROUBLESHOOTING (sheet 2 of 2)
b. TUBE REPLACEMENT. Many differential amplifier
c. Replacement of tubes will not normally necessitate
circuits are critical with respect to the balance between halves
complete recalibration of the 803D. If V202 or V203 is
of differential amplifier tubes. This is especially true of the first
replaced, calibrate the null detector as set forth in paragraphs
stage of amplification. However, the 803D is designed with the
ability to use any 12AX7 for V104 and V105 that meets
V105 will necessitate calibration of the reference supply per
standard
EIA
(Electronics
Industries
Association)
characteristics. Some output voltage drift of the 500 volt
calibrate the AC to DC converter as in paragraph 4-4c.
reference supply may be noted for the first few hours of
d. COMPONENT REPLACEMENT.
Should it ever
operation. This drift will, in most cases, decrease to a small
become necessary to replace a component on a printed circuit
value after the tube has aged a bit. Occasionally a tube with a
board or on the null detector chassis, proceed as follows : .
contaminated grid or extremely poor balance between halves
(1) Clean soldered area around component with
will be found. This tube should be discarded. When replacing
methl ethyl ketone.
reference tube V102, the new tube should be aged at least 150
(2) Remove part and install new component.
hours to realize the high order of stability inherent in the 803D.
(3) Remove flux with du Pont Freon PC.
A tube that has been aged may be obtained by ordering an
0G3-2 from Fluke.
4-3
