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GEK–91584D, Vertical Drilling Motor, Type GE752
32
tion. A reading of one megohm or higher should
be obtained. If necessary, perform additional
cleaning and baking operations to obtain this val-
ue before proceeding.
NOTE: If additional cleaning and baking opera-
tions do not increase the resistance value of the
insulation, it may be necessary to replace the
creepage band and rewind the armature.
2. Measure and record armature resistance. See
the DATA section for values.
3. If there are no armature coils grounded, perform
a bar–to–bar comparison test to check for open
or short–circuited armature coils.
a. Pass a regulated d–c current through the ar-
mature coils.
b. Read the voltage drop between the commu-
tator segments with a millivoltmeter. If the
reading varies more than plus or minus 5%, a
defective or short–circuited coil is indicated. If
the armature fails the bar–to–bar test, the ar-
mature must be rewound.
If the armature will not be rewound, proceed
to inspect the following items.
Insulation
Inspect the insulation of armature coils for cracks,
physical damage, burns and deterioration. If minor re-
pairs are required, refer to Fig. 19 for insulation details.
Glass Band, Commutator End
Inspect the glass bands for split, frayed or loose con-
dition.
Wire Band, Drive End
Inspect the wire band for physical damage, loose tie
clips or broken wire.
Creepage Band
Inspect the surface of the Teflon creepage band for
possible flashover damage. Tap the band lightly and
check for movement of the band to determine if loose. If
the band is loose or has deep burns, replace it. See RE-
PAIR section for instructions.
COMMUTATOR
Check the commutator for threading, pitting, groov-
ing, burns, flat spots, high bars and copper drag.
Check the commutator to make sure that it is not
out–of–round. See the DATA section for concentricity
limits.
Resurfacing
For the resurfacing procedure for a commutator, see
REPAIR, Armature section.
Refer to the DATA section for the minimum permissi-
ble commutator diameter dimension and check the di-
ameter of the commutator.
NOTE: If the brush surface diameter will be less
than the minimum permissible diameter after
resurfacing operations are performed, the com-
mutator must be replaced.
Tightening
If the commutator is loose (has high bars), see the
“REPAIR, Commutator Tightening” section for instruc-
tions to tighten the commutator.
ARMATURE SHAFT INSPECTION
Armature shaft bearing fit dimensions can be
checked and compared to armature shaft drawings pro-
vided in Fig. 20. If the bearing fit dimensions are not
within stated tolerances the shaft must be replaced or
repaired. Refer to Table 2 to determine the correct shaft
drawing for the machine being repaired.
MOTOR FRAME
1. Check the connection strap insulation for dam-
age, signs or burning, cracks or discoloration.
2. Check the insulation on the coils for damage,
signs of burning, cracks or discoloration.
3. Check the lead cables for damage, overheating
and signs of deterioration.