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3-4
TM 55-4920-400-13
Section IV.
ELECTRICAL SYSTEM
3-8. Capacitor Replacement. Remove electro-
lytic filter capacitor from chassis for replacement
as follows:
a. Removal.
(1) Remove chassis assembly from tester case
(para. 2-46).
(2) Unsolder wiring harness leads from termi-
nals on capacitor.
(3) Remove nuts, terminal, and screws secu-
ring bracket and ground leads to chassis.
(4) Remove capacitor and bracket assembly.
b. Installation.
(1) Place capacitor and bracket assembly in
position on chassis, insert screws, install ground
leads and terminal, and secure with nuts.
(2) Solder leads to terminals on capacitor.
(3) Install chassis assembly in tester case
(para. 2-46).
3-9. Transformer. The stepdown transformer is
inspected, replaced, and tested as follows:
a. Inspection.
(1) Inspect transformer for signs of excessive
heat such as melted solder or wax, burned insu-
lation, and odor of burned materials.
(2) Check terminal to see that connections are
tight.
(3) Check leads for shorted or bare wires.
b. Removal. If it is necessary to replace the
transformer, proceed as follows:
(1) Remove chassis assembly from tester case
(para. 2-46).
(2) Unsolder wiring harness leads from termi-
nals on transformer.
(3) Remove nuts, lockwashers and screws se-
curing transformer to chassis, and remove trans-
former.
c. Installation.
(1) Place transformer in position on chassis
and secure with screws, lockwashers, and nuts,
(2) Solder wiring harness leads to terminals
on transformer.
(3) Install chassis assembly in tester case
(para. 2-46).
d. Test.
(1) Insert a variac or an equivalent variable
transformer in the primary circuit of the trans-
former and set the input at 115 volts.
(2) Provide a test setup having a load suf-
ficient to cause a 2,2 ampere flow of current in the
secondary circuit.
(3) Check the voltage across the secondary
output. It should be approximately 26 volts.
3-10. Motor and Pump Assembly, Remove,
clean, and inspect motor and pump assembly as di-
rected in paragraph 2-54; disassemble, as required
to perform the procedures which follow:
a. Inspection. At disassembly, inspect motor
and pump assembly as follows:
(1) Check resistance. between motor input
leads and ground. Reading should be approximately
1,7 ohms.
(2) Check field windings for continuity,
grounds, and shorts.
{3) Examine bearings for excessive wear and
other defects.
(4) Inspect commutator for signs of high mica
at commutator segments.
b. Repair. Replace any defective motor or pump
parts, such as a grounded or shorted field winding
assembly, worn bearings, defective armature or
pump shaft. Repair a commutator which has high
mica by undercutting as follows:
(1) Using an approved method carefully un-
dercut the mica between the commutator segments
to a depth of 0.005 to 0.010 x 3/64 of an inch. Be sure
the full width of the mica is removed and that a thin
(2) Remove all burrs and rough edges from
slots by beveling gently to a 45° chamfer.
(3) Polish with a very fine grade of sandpaper
and finish with felt or canvas.
c. Lubrication. Prior to reassembly of motor
and pump, lubricate motor shaft bearings using
bearing grease, Military Specification MIL-G-
23827, as instructed on the current lubrication
order (Refer to fig. 3-2).
d. Test. Prior to installing the motor and pump
assembly in the chassis, it can be tested as follows:
(1) Arrange the unit in a test setup comprised
of a reservoir, pressure gauge, relief valve (55 psig),
vacuum tank, vacuum gauge, and necessary piping.
(2) Apply 28 vdc power to the motor. In re-
peated tests the pressure gauge should rise consis-
tently to approximately 50 psig. Stop the motor at
this point.
(3) Check the vacuum gauge; it should read
approximately -29.5 Hg.
e. Reassembly and Installation. For reas-
sembly and installation procedures, refer to para-
graph 2-54.
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