(2) Testing Armature.
(a) Testing Armature for grounds. Touch
armature shaft and the end of each commutator bar
with a pair of ohmmeter leads. There should be no
continuity. If continuity is indicatd between
any commutator bar and armature shaft, it indica-
tes a grounded armature. Replace grounded arma-
ture. See figure 5-4.
(b) Testing Armature for shorted Coils.
A growler is necessary to test for shorted coils.
With the armature in the growler, turn the
growler on and hold a thin steel strip parrallel
over the armature surface. Turn qrowler on, and
if the steel strip vibrates or is attracted to the
armature surface, the armature is shorted or
Turn off growler, rotate armature one-
quarter turn and repeat test. Do this for one
complete revolution of armature. See figure 5-5.
If armature has a short or is grounded, replace
(c) Testing Armature for Open Coils.
Test coils for continuity with ohmmeter. Place one
lead on commutator bar, other lead on the next bar.
If there is discontinuity (infinite resistance),
Figure 5-4. Testing Armature for Grounds
Figure 5-5. Testing Armature for Shorted Coils
Figure 5-6 Testing Armature for Open Coils
the reading indicates open coil. See figure
If armature has an open coil, replace it.
C h a n g e 7
5 - 5