Armature Check

Check that the armature coil is not grounded.
Place armature in a growler. See Fig 1.
Hold a thin steel blade parallel and just above while rotating the armature slowly in the growler. A shorted armature will cause a blade to vibrate and attracted to the core. Replace the shorted armature.
Check the insulation between the armature coil cores and the commutator segments. They are normal if there is no continuity. See Fig 2.
Check for continuity between the segments. The condition is normal if there is continuity. See Fig 3.

Fig 1: Placing Armature In Growler

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Fig 2: Checking Armature Coil Ground Test

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Fig 3: Checking Armature Coil Open Circuit

Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.