Bench Testing: Rotor

Check slip ring surfaces for contamination or roughness. Sand surface of rings and clean as necessary. Measure outside diameter of slip rings. Replace rotor if slip ring diameter is not 1.18-1.24". Check resistance of rotor coil across slip rings. Resistance should measure 4.2 ohms at 68°F. If no continuity exists, coil is open and must be replaced. If resistance is substantially lower than specification, coil is shorted and must be replaced. Check for continuity between either slip ring and rotor core. If continuity exists, coil is grounded and must be replaced. Check front and rear bearings for wear or roughness and replace if necessary.