Inspection Procedure

1. Inspect the stator.
1.1. Visually inspect the stator windings:
^ Replace the stator if some coils of wire are darker than others and appear to have overheated.
^ Inspect the 3 phase windings. There are two wires attached to each connector. Replace the stator if any of the wires are loose or broken.
^ Replace the stator if any of the stator windings are damaged.
1.2. Inspect the stator for grounds with a digital multimeter or continuity check. Replace the stator if the windings are grounded to the stator.




2. Inspect the drive end assembly.
2.1. Inspect the drive end bearing by spinning the rotor by hand. If the rotor does not spin freely, has a rough feel, or is noisy, replace the drive end frame.
2.2. Inspect the slip rings on the rotor.
2.2.1. If the slip rings are rough or dirty, spin the rotor while holding a 40-grain polishing cloth around the rings.
Blow away all the copper dust.
2.2.2. Replace the rotor if the slip rings are damaged or cannot be cleaned to a smooth condition.




3. Inspect the rotor windings with a digital multimeter.
^ The rotor windings should not be grounded (1).
^ The rotor windings should not be an open circuit (2).
^ The resistance should be between 2.1-2.4 ohm (2) at room temperature. Replace the rotor it the windings are grounded, open or have incorrect resistance.




4. Inspect the slip ring end assembly.
4.1. Inspect the diodes in the rectifier bridge with a digital multimeter.
4.1.1. There should be continuity in one direction between each of the 3 phase clips (1) and the grounded heat sink (2). When the polarity of the digital multimeter is reversed, all 3 readings should show open circuits.
4.1.2. There should be continuity in one direction between each of the 3 phase clips (1) and the positive heat sink. When the polarity of the digital multimeter is reversed, all 3 readings should show open circuits.
Replace the rectifier bridge when one or more of the readings do not follow this pattern.
4.2. Inspect the slip ring end bearing. Replace the bearing if the bearing is dry or damaged.
4.3. Inspect the brush holder assembly.
4.3.1. Replace the brush holder assembly if the brushes are damaged or broken, or if they are worn to less than 10 mm (0.4 in) in length.
4.3.2. Replace the brush springs if the springs are damaged or broken.
4.4. Replace the voltage regulator if no other problems are found that can cause an existing high, low or no output condition.