TM 55-4920-328-13
Section III. TROUBLESHOOTING PROCEDURES
5-19.
Electrical
System
Troubleshooting
Procedures.
a. Troubleshooting of METS electrical systems
consists essentially of continuity checkout and the
isolation of open circuits, shorts, and grounded circuits.
Signal and power voltages are provided in the circuits
shown in figures FO-2 through FO-27. Test points on
the system schematics are shown as numbers inscribed
in a star symbol. Located at the back of this chapter are
figures 5-3 through 5-46 which will aid the technician.
No special or unique test equipment is required to
isolate trouble in a faulty circuit. Prior to troubleshooting
a system or functional loop, a review of the chapter I
description and operational theory pertaining to a
component or system should be accomplished. A
thorough understanding of the operation of an electrical
system will aid in trouble isolation. It is also
recommended that only experienced electrical and
electronics technicians be used during troubleshooting.
Voltages and currents in the output circuits of the diesel
engine ac generator set and the 24 volt dc battery
circuits in the electric start system are sufficiently high to
cause serious or fatal injury to maintenance personnel.
Observe all base safety regulations.
WARNING
Deenergize the generator set as outlined in
chapter 2 of this manual and attach a warning
tag to the generator control panel (figure 2-8)
prior to any maintenance action. Failure to
observe
this
warning
could
permit
the
electrical
system
to
be
energized
with
consequent
serious
or
fatal
injury
to
maintenance personnel.
b. Prior to troubleshooting and when instructed in
the text, ensure that the generator set is deenergized
and that no electrical power is present in METS systems
circuitry. Attach a warning tag to the generator control
panel to warn personnel that troubleshooting is being
performed, to avoid inadvertent electrical shock with
serious or fatal consequences. When checking power or
signal voltage and current at test points, exercise
extreme caution. Prior to isolation of sub-loops and
components, check for defective fuses and panel lights.
Accomplish continuity checks of systems assembly
circuitry using a multimeter, set on the resistance scale.
Check wire runs and cabling for opens, shorts, grounds,
pinto-pin shorts, and high resistance solder joints in
signal distribution circuits. Check all shields for
electrical integrity. Observe all applicable safety
regulations.
When
required,
calibrate
panel
instrumentation in accordance with TB 55-4920-328-50.
Remove defective parts and install replacement parts as
outlined in the removal and installation procedures
outlined in chapter 6. Accomplish minor repair of the
unit as specified in chapter 6. Troubleshooting of
certain
systems
listed
in
the
following
text
is
accomplished by the use of standard test equipment and
consists of ascertaining that continuity, wire routing,
cabling interconnection, voltage levels, polarity, and
frequency requirements of a system agree with the
requirements shown in the system schematics. After the
faulty component is isolated and removed, install a new
component of like part number. (Refer to chapter 7 for
part number identification.) Recalibrate the system after
installation of the new component.
5-20. Troubleshooting Procedures.
Table 5-4 provides information useful in diagnosing and
correcting unsatisfactory operation or failure of the
METS. Each trouble indication stated is followed by a
list of possible trouble. The remedy recommended is
described in the last column. Operational trouble
beyond the scope of this table will require a complete
system by system check, using the schematics
contained in this chapter.
5-11
