What was found
(CAN) THE ACFT WAS POWERED BY APU GENERATOR ONLINE. AFTER 30 MINS, WHEN THE HYDRAULIC PUMP TURNED ON, THE FOLLOWING CIRCUIT BREAKER WAS POPPED OUT, 115 VAC ESS FEED, ESSAC TRANSFER CONT). THE SMOKE CAME FROM BEHIND THE CAPTAIN SIDE CIRCUIT BREAKER PANEL CBP-3. AFTER INSPECTION, WE FOUND THAT THE JB18 HAD A BURNED MARK ON ACESS VOLT/FREQUENCY SENSOR, A1XD, CONNECTOR P1XD AND ITS ASSOCIATED WIRING.