present and the armature should be replaced.
If the field coils are defective, replace
(g) Check armature for short circuits by the use of
(e) Repair or replace defective items as
a growler. Revolve armature in a growler with
a steel strip such as a hacksaw blade held
over the core and parallel to the shaft. The
blade will vibrate above the short circuit if one
(a) Be certain that all coils are pressed into core
If an external examination
slots and soldered to commutator risers.
discloses nothing to cause a short circuit, such
(b) Inspect core for deep nicks and cuts.
as foreign material between the bars of the
(c) Inspect commutator for rough surface or other
commutator, the armature is unserviceable.
indications of wear.
(h) To test for out-of-round, place the armature
(d) Inspect shaft bushing seats for wear.
with the shaft on V-blocks and mount the dial
(e) Inspect and test each commutator segment
indicator so that its plunger rests against the
for ground. Use testing device (d(1)(d) above)
commutator. Rotate the armature slowly, and
and proceed as follows: Place the armature
note the variations in thousandths shown on
on a V-block, and touch one test probe to
the face of the dial indicator. The variation is
either the core or the shaft of the armature
the ex-tent to which the armature is out-of-
and the other probe to each commutator
round and is referred to as run-out. If the
If a commutator segment is
commutator is more than 0.003 inch out-of-
grounded, the lamp will light. Using a dry
round, place the armature in a lathe and ma-
brush, a cloth, or compressed air, clean
chine it to proper specifications. Re-move all
between the metal strips on the commutator;
burs with No. 00 sandpaper; then undercut
then retest it. If the segment is still grounded,
the armature is unserviceable.
(i) Inspect drive end bearing for roughness.
(f) Check armature for grounding by placing one
(j) Repair defective items as authorized or
test prod on the end of the commutator and
the other test prod on the laminated core or
e. Assembly. Reverse procedures in b above.