Figure 7-58. - Testing for grounds in armature windings.
armature while you hold the test blade stationary. If there is a short in the armature windings, the test blade will be attracted to the armature (magnetized) and will vibrate.
Figure 7-59. - Testing for shorts in armature windings
CAUTION Place the test set switch in the off position before removing the armature, and never leave the test set turned on unless there is an armature placed in the core.
When you are testing an armature for an open circuit, place the armature in an armature test set and turn the test set ON. Place the armature double prods on two adjoining commutator segments and note the reading on the ammeter, as shown in figure 7-60. Rotate the armature until each pair of adjoining commutator segments have been read. All the segments should read the same. No reading indicates an open circuit, and a high reading indicates a short circuit.
CAUTION Place the test set switch in the off position before removing the armature from the test stand.
Check the commutator for broken leads. Repair and resolder any you find. If you find an open winding, check the commutator for burned spots. They reveal the commutator segment to which the open winding is connected. Open circuits in the windings generally occur at the commutator and can be found by a visual inspection. If there is excessive sparking at the brushes with the motor reassembled, disassemble it and replace the armature.
Figure 7-60. - Testing for opens in a commutator.Continue Reading