Illus 89 Removing Field Coils

Testing Armature

To Test for "Ground":

If growler with test points is available, test as shown in Illus. 90. If this means of testing is not available, test with battery and ammeter hook-up, same as used for testing field coils. Contact commutator with one test point and armature core with the other. If circuit is completed, armature is grounded.

If armature is found to be grounded, make sure commutator is free from carbon and copper dust deposits. After cleaning thoroughly between segments and at ends of commutator and blowing off thoroughly with compressed air, repeat test. If ground still exists, armature must be replaced with a new one.

"Growler" Test for "Short":

Place armature in "growler" and hold piece of hacksaw blade in loose contact with armature core as shown in Illus. 91. Turn "growler" "ON". Rotate armature slowly one or more full turns. If armature is shorted, hacksaw blade will be attracted to armature core and will vibrate violently at one or more points around armature.

If short is found, clean thoroughly between commutator segments as described under "ground" test, and test again. If short still exists, armature must be replaced with a new one.

"Growler" Test for "Open":

Place armature in "growler" as shown in Illus. 92 and turn "growler" "ON." Insert tip of hacksaw blade between segments that are closest in alignment with the point of contact of armature core and "growler" V. Make and break contact between segments with hacksaw blade.

HACKS*W BLADC

HACKS*W BLADC

illus. 91

testing armature for "short"

illus. 91

testing armature for "short"

A strong flash should be seen as contact is broken. No flash or a very weak flash indicates an open circuit.

Repeat this test between all segments, turning armature so that each test is made on the line of contact between armature core and "growler" V. If an open circuit is found check for loose or broken wires at commutator connections. If none are found that can be repaired, armature must be replaced with a new one.

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