CHAPTER 2
FOURTH ECHELON MAINTENANCE
Section I. GENERAL TROUBLESHOOTING TECHNIQUES
Warning: When servicing the TS-1777/VRM-1, be careful when working near power
connections. Injury may result from contact with these connections.
or assemblies are at fault by the following
28. General Instructions
methods:
Troubleshooting of Test Set, Radio AN/
(1) Visual inspection. The purpose of
VRM-1 at the fourth echelon includes all
visual inspection is to locate faults
the techniques outlined for organizational
without testing or measuring cir-
maintenance and additional techniques re-
cuits. Cables, connectors, indi-
quired to localize troubles to a particular
cator lamps, and the fuse should
plug-in assembly board to isolate a de-
be inspected and an attempt made to
fective part on the front panel and the
localize the fault to a particular
selector switch. These fourth echelon pro-
assembly.
cedures are not complete in themselves
(2) Operational tests. O p e r a t i o n a l
but supplement the procedures described
tests frequently indicate the gen-
in TM 11-6625-496- 12. The systematic
eral location of trouble. In many
troubleshooting procedure, which begins
instances, the tests will help in
with the operational and equipment per-
determining the exact nature of the
formance checklists that can be performed
fault. The equipment performance
at the organizational level, must be com-
checklist (TM 11-6625-496-12) is
pletely by means of localizing and isolating
a good operational test.
techniques. Paragraphs 31 through 34 pro-
(3) Troubleshooting Chart. The trou-
vide localizing and isolating techniques for
ble symptoms listed in the chart
use by fourth echelon personnel. Para-
trouble to-an assembly or part.
repair instructions, and paragraphs 41 and
c. Isolation. The tests listed below will
aid in isolating the trouble. After the trou-
justment of the AN/VRM-l.
ble has been localized to an assembly,
isolate the trouble within the assembly by
29. Organization of Troubleshooting
voltage, resistance, and continuity meas-
Procedures
urements.
a. General. The first step in servicing
(1) Voltage and resistance measur-
a defective AN/VRM-l is to localize the
ements. This equipment contains
fault. Localization means tracing the fault
transistors. Observe all precau-
to a plug-in assembly board, the front
tions to prevent damage to transis-
panel, or a cable. The second step is to
tors. Make voltage and resistance
isolate the fault. Isolation means tracing
measurements only as specified.
the fault to a defective part responsible
When measuring voltages, use tape
for the abnormal condition. Some faults,
or sleeving to insulate the entire
such as burned-out resistors, can often be
test prod, except for the extreme
located by sight or smell. The majority of
t i p . A momentary short circuit
faults, however, must be isolated by check-
can ruin the transistor. Use the
ing voltages or resistances.
resistor and capacitor color codes
b. Localization. The first step in finding
a trouble is to determine which assembly
components. Use the resistance
17
