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Page Title:
Figure 3-4. Removing Retainer from Snap Ring |
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 TM 10-3930-644-14 & P
If the commutator is worn, dirty, out of round, or
has high insulation, the commutator should be
turned down and undercut as previously
described.
3. Field Coils
The field coils should be checked for grounds
and opens using a test lamp.
a. To chec k for grounds, disconnect the field
coil ground connections. Connect one
test prod to the field frame and the other
to the field connector. If the lamp lights,
the field coils are grounded and must be
repaired or replace.
b. To check for opens, connect test lamp
prods to ends of field coils. If lamp does
not light the field coils are open.
Figure 3-4. Removing Retainer from Snap Ring
If the field coils need to be removed for repair or
2. Armature
replacement, a pole shoe spreader and Pole
shoe screwdriver should be used. Care should
The armature should be checked for short
be exercised in replacing the field coils to
circuits. opens and grounds.
prevent grounding or shorting them as they are
tightened into place. Where the pole shoe has a
a. check armature for shorts by placing it on a
long lip on the side, it should be assembled in
"growler", and with a steel strip or a hack saw
the direction of armature rotation.
blade held on armature core, rotate armature. If
blade vibrates, armature is shorted in area of the
H. REASSEMBLY
core below the vibrating blade. Copper or brush
dust in slots between communicator bars
1. Place the clutch assembly on the armature
sometimes causes shorts which can be
shaft. To facilitate replacing the -nap ring and
eliminated by cleaning out slots. Shorts or
retainer onto the armature.
crossovers of coils at core end can often be
eliminated by bending wire slightly and
a. Place the retainer on the armature shaft
reinsulating exposed bare wire. If short cannot
with the -upped surface facing the snap
be eliminated armature must be replaced.
ring groove.
b. Opens may be located by inspecting the points
b. Place the snap ring on the end of the
wire the conductors are Joined to the
shaft. With a piece of wood on top of it,
commutator for loose connections.
Poor
force the ring over the shaft with a light
connections cause arcing and burning of the
hammer blow (See Figure 3-5), then slide
commutator. If the bars are not badly burned,
the ring down into the groove.
resolder the leads in the riser bars and turn the
commutator down in a lathe. Then undercut the
c. To force the retainer over the snap ring,
insulation between the commutator bars .031".
place a suitable washer over the shaft and
squeeze retainer and washer together
c. Grounds in the armature can be detected by the
with pliers (See Figure 3-6).
use of a test lamp. If the lamp lights when one
test prod is placed on the commutator and the
d. Remove the washer.
other test prod on the armature, the armature is
grounded.
2. Refer to the disassembly procedure and follow
in reverse to complete the reassembly.
R-146-1
3-95
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