TM 11-6625-1633-45
CHAPTER 3
GENERAL SUPPORT MAINTENANCE
checks, observations, and measurements before the
3-1. General Maintenance Instructions
cause of a trouble is revealed.
a. The maintenance procedures performed at the gen-
eral support category of maintenance are actions which
a. The first step in servicing a defective equipment is
have been designed to anticipate potential problem areas
to sectionalize the fault. Sectionalization means tracing
for the purpose of correcting a possible trouble before it
the fault to the major equipment component. The second
results in equipment outage. The action to be taken con-
step is to localize the fault. Localization means tracing
sists mainly of the following:
the fault to the defective stage. The third step, isolation,
means tracing the fault to the defective component part.
(1) Visual inspection of the equipment for the pur-
Some faults, such as burned out resistors, can often be
pose of determining general condition, unusual noise,
isolated by sight, smell, or hearing. The majority of
and observing meter indications. Generally, the equip-
faults, however, must be isolated by checking voltages,
ment will remain operational when these inspections are
resistances, and signal levels.
made.
(2) Repair or replacement of parts that have a
b. Whenever an equipment trouble occurs, make a
definite life expectancy.
visual inspection of all equipment controls, and cable
connections before performing any detailed trouble-
b. The general support maintenance procedures are
shooting procedures. When the trouble has been isolated
not complete in themselves but supplement the proce-
to a particular functional group, isolate the trouble to the
dures performed at the organizational category and in-
defective assembly or unit.
clude any additional techniques required to perform
maintenance on the AN/URM-149.
c. In performing the localization and isolation proce-
dures outlined in a and b above, one or more of the
3-2. Tools, Materials, and Test Equipment
techniques specified below may be applied.
Required
CAUTION
a. Multimeter TS-352B/U.
Before connecting the signal generator to
the ac power input source, check the posi-
tion of switch S9. Operation of the signal
generator from a 230 vac power source
with switch S9 in the 115V position may
cause serious damage to the equipment.
(1) Voltage measurements. Portions of the
e. Frequency Meter TS-186/UP.
equipment are transistorized. When measuring voltages,
use tape or sleeving (spaghetti) to insulate the entire test
f. Modulation Meter ME-57/U.
prod, except for the extreme tip. A momentary short can
damage a transistor. Use the same or equivalent elec-
tronic multimeter specified on the voltage and resistance
diagrams.
h. Electronic Equipment Tool Kit TK-100/G.
(2) Resistance measurements. Make resistance
3-3. Troubleshooting Techniques
measurements only as directed on voltage and resistance
diagrams or charts. For transistorized circuits, use only
To be effective, troubleshooting must be systematic; it
the ohmmeter ranges specified; otherwise, indications
will be necessary to perform a sequence of operational
obtained will be inaccurate.
3-1
