What was found
DURING TRANSIT , APU RUNNING SUPPLIED BOTH ELEC.POWER AND AIR CONDITION, THE ELECTRICAL POWER ON / OFF INTERMITTENTLY, AND FINALLY ELEC.POWER DISCONNETED. AFTER THAT, THE SMOKE CAME OUT AT REAR CABIN AREA. MAINTENANCE CHECKED FOUND APU RPM WILL FLUCTUATED WHEN SUPPLIED BOTH ELEC. POWER AND PNEUMATIC. AFTER REPLACED THE APU FCU , CORRECT THE PROBLEM. MAINTENANCE ALSO CHECKED THE APU SUPPLIED ELEC.CIRCUIT, POWER RELAYS , NO ANOMALY FOUND.