What was found
(CAN) DURING WALK-AROUND, DC PWR HAD BEEN APPLIED AND ONLY ENGINE DISPLAY AND NR 2 MFD HAD BEEN TURNED ON. SHORTLY AFTER (AROUND 1MIN) BIG GREEN T FOR THE TESTING MODE FLASHED ON NR 1 MFD (NOTICE THAT THE SWITCH FOR THIS MFD WAS STILL OFF). A BURNED ODOR CAME FROM WAY BACK IN CABIN ACCOMP AGAIN WITH A THICK SMOG. SMOKE CAME FROM FAULTY DISPLAY UNIT & SPREAD INSIDE CABIN THRU INSTRUMENT COOLING DUCTS, WHICH ARE CONNECTED TO CABIN VENT SYS. AFTER A SHORT INVESTIGATION, BREAKER FOR NR 1 MFD FOUND OUT. NR 1 MFD FOUND TO BE INTERNALLY DEFECTIVE CAUSING BREAKER TO COME OUT & SMOKE & BURNED ODOR INSIDE CABIN. TROUBLESHOOTING SWITCH FOR FAULTY DISPLAY UNIT DID NOT HAVE TO BE ON TO CAUSE BREAKER TO COME OUT.