Robert Bosch Starting Motor Repair
TESTING ARMATURE FOR SHORT CIRCUIT
Place armature in a growler and hold hacksaw blade
above each slot while slowly rotating the armature.
If coil is shorted, the blade will be attracted to and
repelled from the slot.
Short circuit most often occurs because of copper dust or
filings between two commutator segments. Clean
commutator segments to correct this short.
Place one test lead on commutator segment. Place other
test lead on an adjacent segment. Repeat this operation
for all segments by moving one lead at a time.
If the test meter indicator does not swing to zero and
remains stationary, the armature coil between these two
segments is open. Replace armature.