Specifications

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.
28. General Instructions
Troubleshooting of Test Set, Radio AN/
VRM-1 at the fourth echelon includes all
the techniques outlined for organizational
maintenance and additional techniques re-
quired to localize troubles to a particular
plug-in assembly board to isolate a de-
fective part on the front panel and the
selector switch. These fourth echelon pro-
cedures are not complete in themselves
but supplement the procedures described
in TM 11-6625-496- 12. The systematic
troubleshooting procedure, which begins
with the operational and equipment per-
formance checklists that can be performed
at the organizational level, must be com-
pletely by means of localizing and isolating
techniques. Paragraphs 31 through 34 pro-
vide localizing and isolating techniques for
use by fourth echelon personnel. Para-
graphs 35 through 40 provide detailed
repair instructions, and paragraphs 41 and
43 contain a procedure for the overall ad-
justment of the AN/VRM-l.
29. Organization of Troubleshooting
Procedures
a. General. The first step in servicing
a defective AN/VRM-l is to localize the
fault. Localization means tracing the fault
to a plug-in assembly board, the front
panel, or a cable. The second step is to
isolate the fault. Isolation means tracing
the fault to a defective part responsible
for the abnormal condition. Some faults,
such as burned-out resistors, can often be
located by sight or smell. The majority of
faults, however, must be isolated by check-
ing voltages or resistances.
b. Localization. The first step in finding
a trouble is to determine which assembly
or assemblies are at fault by the following
methods:
(1)
(2)
Visual inspection. The purpose of
visual inspection is to locate faults
without testing or measuring cir-
cuits. Cables, connectors, indi-
cator lamps, and the fuse should
be inspected and an attempt made to
localize the fault to a particular
assembly.
Operational tests. Operational
tests frequently indicate the gen-
eral location of trouble. In many
instances, the tests will help in
determining the exact nature of the
fault. The equipment performance
checklist (TM 11-6625-496-12) is
a good operational test.
Troubleshooting Chart. The trou-
ble symptoms listed in the chart
(para 33) will aid in localizing a
trouble to-an assembly or part.
(3)
c. Isolation. The tests listed below will
aid in isolating the trouble. After the trou-
ble has been localized to an assembly,
isolate the trouble within the assembly by
voltage, resistance, and continuity meas-
urements.
(1) Voltage and resistance measur-
ements. This equipment contains
transistors. Observe all precau-
tions to prevent damage to transis-
tors. Make voltage and resistance
measurements only as specified.
When measuring voltages, use tape
or sleeving to insulate the entire
test prod, except for the extreme
tip. A momentary short circuit
can ruin the transistor. Use the
resistor and capacitor color codes
(fig. 35 and 36) to find the value of
components.
Use the resistance
17