CHAPTER 6
FIELD MAINTENANCE
Note
This chapter contains information for field maintenance. The amount of repair that can be
performed by units having field maintenance responsibility is limited only by the tools and test
equipment available and by the skill of the repairman.
Section I. TROUBLESHOOTING AT FIELD MAINTENANCE LEVEL
(2) Operational tes.t The operational test is
Warning:
used to check all functions of the signal
When servicing Signal Generator SG-
generator.
When making this test.,
3/U, be extremely careful of exposed
manipulate all of the front-panel controls and
high voltages. Dc potentials as high as
switches and see that all controls operate
400 volts are present.
When
smoothly, both mechanically and electrically.
measuring tube socket or terminal
Connect the output of the signal generator to
voltages, keel) one hand clear' of the
a reliable fm receiver. Check the frequency
equipment at all times. Before making
output of the signal generator on all three
resistance measurements or removing
bands, at different output levels, at all
defective parts, be sure to disconnect
modulation frequencies, and at different
plug P1 from the power receptacle, and
deviation levels. Refer to the equipment
be sure to discharge filter capacitors
performance check list (para. 39) for
C84 and C85.
probable troubles and their locations.
(3) Tube test Most troubles encountered in
.
53. Troubleshooting Procedures
electronic equipment can be attributed
a. General. The first procedure in servicing a
directly to defective vacuum tubes. Before
defective signal generator is to isolate the fault to a major
proceeding with a point-by-point check of the
circuit or circuits. After isolating the fault to a specific
signal generator, test the vacuum tubes
circuit, localize the defect to a specific part or parts.
associated with the suspected faulty circuit.
Burned-out resistors, arcing, or shorted transformers can
be located by sight or smell. The majority of part failures
Caution:
may be localized by making voltage and resistance
To prevent misalignment of the signal
measurements.
generator, be sure to replace each
b. Localization of Defects. If proper results are not
tested tube in its original socket.
obtained when testing or alining a receiver with Signal
Generator SG-3/U, the signal generator may be at fault.
(4) Troubleshooting chart The troubleshooting
.
To check the generator, make a careful visual inspection
chart (para. 59) will aid greatly in localizing
and operational test ((1) and (2) below) to sectionalize
the trouble.
and localize the trouble. If the defect is not immediately
(5) Power supply test. If the preceding tests fail
apparent, proceed with the troubleshooting procedures
to localize the trouble, check the power
outlined in (3) through (6) below.
supply for proper operation in accordance
(1) Visual inspection
.
A careful visual
with procedures outlined in paragraph 58.
inspection with the equipment in an
(6) Intermittent trouble In all of these tests, the
.
operating or nonoperating state often will
possibility of intermittent faults should not be
provide a clue as to the exact location of an
overlooked. If present, this type of trouble
existing defect.
Even with the signal
sometimes can be detected by tapping or
generator in proper' operating conditions, a
jarring the unit.
periodic visual inspection will aid ill
forestalling equipment failures. Refer to
for
visual
inspection
procedure.
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