TM 11-6625-847-45
except for the extreme tip.
applicable to this equipment are listed in (1) and (2) below
and should be used to localize the trouble to a stage
(2) Resistance
measurements
.Make
within a defective functional circuit.
resistance measurements only as directed
in the troubleshooting charts and schematic
(1) Troubleshooting chart. The troubleshooting
diagrams and in paragraph 2-17.
charts, paragraphs 2-18 through 2-23, list
the symptoms of common troubles
CAUTION: Before using any ohmmeter
occurring within the modules and,
to test transistors or transistor circuits,
subassemblies of the SM-442A/GRC and
check the open-circuit voltage across
give (or references) corrective measures.
the ohmmeter test leads Do not use an
The troubleshooting chart are to be used in
ohmmeter or a multimeter it the open-
conjunction with the performance tests
circuit voltage exceeds 1.5 volts.
given in paragraphs 4-1 through 4-12 as
Since the Rx1 range
normally
described in paragraph 2-4. The charts do
connects the ohmmeter internal
not list all the troubles that may occur. The
battery directly across the test leads,
repairman should use these charts as a
the comparatively high current (50 ma
guide in analyzing symptoms that are not
or more) may damage the transistor
listed.
under test. The Rx1 range of any
ohmmeter should not be used when
(2) Stage gain charts. The stage gain charts
testing low-powered transistor
difficult troubles that produce weak signals
in amplifier modules AR1 through AR5 and
(3) Intermittent troubles.
In all tests, the
IF amplifier module Al.
possibility of intermittent troubles should not
be overlooked. If present, this type of
(3) Wave shapes. When troubleshooting the
trouble often may be made to appear by
pulse generator module, compare the wave
tapping or jarring the equipment. Make a
shapes in figure 1-17 with those obtained
visual inspection of the wiring and
using the procedures in paragraph 2-10 and
connections to the units of the SM-
troubleshooting chart 2-19
442A/GRC. Minute cracks in printed circuit
boards can cause intermittent operational A
d. Isolate Once the trouble has been localized to a
magnifying glass is helpful in locating
particular stage of a functional circuit, the faulty
defects in printed boards.
components responsible for the malfunction can be
measurements of printed conductors may
isolated by applying one or more of the following
be made using the same techniques
procedures:
ordinarily used on hidden conventional
wiring; follow the ohmmeter precautions in
(2) above
(1) Voltage measure.
Th is equipment is
transistorized.
When making voltage
measurements, use the same voltmeter
2-3. Test Equipment
specified ill the troubleshooting charts and
the schematic diagrams of the modules and
The chart below lists the test equipment required for
subassemblies.
Use tape or sleeving
troubleshooting the SM-442A/GRC.
(spaghetti) to insulate the entire test prod,
Test equipment
Technical manual
Federal stock No.
Multimeter AN/PSM-6B
TM 11-6625-475-10
6625-643-1686
Voltmeter, Electronic AN
TM 11-6625-475-10
6625-973-3986
URM-145
2-2
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