lamp lights, indicating a ground, and if the ground is not apparent and repairable, replace the
armature.
(b) Open. An open-circuited armature is easily detectable, since this condition produces badly burned
commutator bars. The bars connected to the open armature coils soon burn, since every time they
pass under the brushes they interrupt a flow of current, causing heavy arcing. Check the armature
coil continuity with a test light. If one or more coils are open, replace the armature.
(c) Short (fig. 80). A shorted armature may be detected on a growler. When an armature is placed on
the growler, and a hacksaw blade held above each armature coil, the blade will be alternately
attracted to and repelled from a shorted armature coil. Replace a shorted armature. Before
discarding an armature, inspect the commutator slots. Copper and brush dust sometimes collects in
the slots and shorts adjacent bars.
(3)
Field. Test the field coil current draw by connecting a battery and an ammeter between the two field
leads. The current draw at 24-volts should be from 0.66 to 0.74 amperes. Replace the frame and field
assembly if the field coil current is not between the limits specified.
(4)
Brushes. Replace the brushes as instructed in paragraph 92b.
(5)
Brush springs. The brush springs must have enough tension to provide proper pressure between the
brushes and the commutator after the generator is assembled. After reassembling the brushes, brush
springs, and brush arms to the commutator-frame end, place the commutator in position and check with
a spring scale the amount of pull needed to raise the brush arms from the brushes. Replace the springs
if the tension is not 28 ounces.
(6)
Bearings. Replace the ball bearings if they roll rough, or sloppily. Otherwise, clean the bearings by
rotating them in carbon tetrachloride, or similar solvent. Dry them with compressed air and immediately
relubricate with grease, ball and roller bearing BR.
(7)
Commutator-end frame. Replace the commutator-end frame if the holders or pins are damaged in any
way. The frame is of riveted construction and must be replaced as a unit.
e. Reassembly (fig. 78). Install the outer bearing retainer plate (32) in the drive-end frame (33). Place the drive end
bearing
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