What was found
REPORTED ELECTRICAL ODOR IN CABIN DURING PUSHBACK. MAINTENANCE FOUND APU STARTER ON FIRE. MAINTENANCE PUT OUT FIRE WITH PORTABLE FIRE EXTINGUISHER, PULLED AND COLLARED APU CONTROL AND STARTER CIRCUIT BREAKERS. APU REMOVED AND COMPARTMENT CLEANED. APU, LT APU ACCESS DOOR, INSULATION BLANKETS, STARTER LEADS, ECU AND R2-63 START RELAY REPLACED. REPAIRING TERMINAL AT NR 3 BATTERY DISCONNECT. APU RETURNED TO SERVICE.