FIELD MAINTENANCE
Note. This chapter contains information for field maintenance. The amount of repair that can be performed by units
having field maintenance responsibility is limited only by the tools and test equipment available and by the skill of the
repairman.
Section I. TROUBLESHOOTING AT FIELD MAINTENANCE LEVEL
voltages exposed. Potentials as high as 1,000 volts at 1,800 cycles ac may be developed in the
amplifier circuit. Potentials as high as 1,250 volts at 60 cycles ac and 450 volts dc are developed in
Rectifier Power Unit PP-86(*)/TXC-1. When measuring high voltages with a probe, try to keep one
hand in the pocket. Before touching any part after the voltage has been turned off, short-circuit the
part to ground.
parts in the facsimile transceivers. Fig-
ures 152 through 156 refer to the recti-
a. General. The first step in servicing a defec-
fier power units.
tive facsimile transceiver is to sectionalize the fault.
(2)
Resistance measurements. These measure-
Sectionalization means tracing the fault to a major
ments (par. 88) prevent further damage
component or circuit responsible for abnormal
to the transceiver from possible short cir-
operation. The second step is to localize the fault.
cuits. Resistor and capacitor color codes
Localization means tracing the fault to the defec-
tive part responsible for the abnormal condition.
values of components.
Some faults, such as burned-out resistors, arcing,
(3)
Operational test. The operational test is
and shorted transformers, often can be located by
important as it may indicate the location
sight, smell, and hearing. The majority of faults,
of trouble. In many instances, the in-
however, must be localized by checking voltages
formation gained may determine the ex-
and resistances.
act nature of the fault. To utilize this
b. Component Sectionalization and Localization.
information fully, all symptoms must be
Listed below is a group of tests arranged to simplify
interpreted in relation to one another.
and reduce unnecessary work, and aid in tracing a
Troubleshooting chart. The trouble symp-
(4)
trouble to a specific component. The simple tests
toms listed in this chart (par. 89) will aid
are used first. Those that follow are more compli-
greatly in localizing trouble.
cated. Follow the procedure in the sequence
(5)
given. A serviceman must be careful not to cause
is helpful in troubleshooting as it will
further damage to the transceiver while it is being
isolate the specific circuit at fault.
serviced. In general, the trouble is traced to a
(6)
section of the transceiver, and the faulty com-
These diagrams are included as an aid in
ponent in that section is located; then the trouble
locating faulty parts.
is remedied. The service procedure is summarized
as follows:
(7)
(1) Visual inspection. The purpose of visual
171). These schematic diagrams will aid
inspection (par. 54) is to locate any visible
in tracing troubles to individual com-
trouble. Through inspection alone, the
ponents or circuits.
repairman frequently may discover the
(8)
Intermittents. In all these tests, the pos-
trouble or determine the circuit in which
sibility of intermittent conditions should
the trouble exists. This inspection is
not be overlooked. If present, this type
valuable in avoiding additional damage
of trouble often may be made to appear
which might occur through needless and
by tapping or jarring the equipment. It
improper serficing methods and in fore-
is possible that some external source may
stalling future failures. Figures 129
cause the trouble. Test wiring for loose
through 151 will aid in identification of
connections and move wires and compo-
