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Page Title:
CHAPTER 3. THIRD ECHELON MAINTENANCE |
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|  T H I R D ECHELON MAINTENANCE
Section I. GENERAL TROUBLESHOOTING TECHNIQUES
Warning: Be extremely careful when servicing the RT-505/PRC-25. During opera-
tion, 125 volts dc exists at the plate circuit of the power amplifier.
c. Localization and Isolation. The pro-
cedures given in (1) through (3) below will
Third echelon maintenance procedures
aid in localizing and isolating the trouble.
Localize the trouble to an area, and then
tenance procedures described in TM 11-
isolate the trouble to a defective part. Use
5 8 2 0 - 3 9 8 - 1 0 and TM 11-5820-398-20.
the following methods:
Third echelon maintenance includes sys-
(1) Troubleshooting chart. The trou-
tematic troubleshooting procedures (para
ble symptoms listed in the trouble-
shooting chart (para 38) will aid in
localizing and isolating trouble to
ing power amplifier tank module A2, vari-
a part or to an assembly.
able frequency oscillator module A9, and
(2) Voltage and resistance measure-
sidestep oscillator module A20 (para 43
ments. Most troubles must be lo-
through 45).
cated by voltage and resistance
measurements. The RT-505/PRC-
35.Organization of Third Echelon Trouble-
25 is transistorized. Observe the
shooting Procedures
following precautions to prevent
a. General. The first step in trouble-
transistor damage. Make voltage
shooting a defective RT-505/PRC-25 is to
and resistance measurements only
sectional ize the fault to a major area such
as specified. When measuring
as the power supply, function switch cir-
voltages, use tape or sleeving to
cuits, or case wiring. The second step is
insulate the entire test probe, ex-
to localize the fault to a defective assembly
cept the extreme tip. A momentary
or area. The third step is to isolate the
short circuit can ruin a transistor.
faulty part or circuit board within an as-
(For example, if the bias is shorted
sembly.
out, excessive current between the
b. Sectionalization. The following group
emitter and the base may ruin the
of tests is arranged to reduce unnecessary
transistor.)
work and to aid in troubleshooting a de-
(3) Intermittent troubles. The possi-
fective RT-505/PRC-25. Sectionalize the
bility of intermittent troub1es
trouble to faulty units by following the pro-
should not be overlooked. If pre-
cedures listed in (1) and (2) below:
sent, this type of trouble may often
(1) Visual inspection. Visual inspec-
be made to appear by tapping or
tion may locate faults without test-
jarring the RT-505/PRC-25. Check
ing or measuring the circuits.
the wiring, the connections, and the
(2) Operational tests. O p e r a t i o n a l
plugs and jacks of the various mod-
tests frequently indicate the gen-
ules.
eral location of a trouble. In many
instances, operational tests, such
as the equipment performance
Required
checklist (TM 11-5820-398-20),
The following charts list the equipment
will help in determining the exact
nature of the fault.
required for troubleshooting the RT-505/
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