What was found
APU FIRE DETECTION TEST WILL NOT TEST. "DEFERRED APU PER MEL 49-1; CAT. "C"; ASSIGNED DMI 13486; PLACARD INSTALLED. TROUBLESHOOTING SYSTEM, CHECKED TEST SWITCH FOR CONTINUITY BETWEEN PINS 2 & 3; CHECKED GOOD. VERIFIED THAT SENSOR/ RESPONDER IS HEATING UP WITH TEST SWITCH DEPRESSED, HOT TO THE TOUCH. RESET ALL CIRCUIT BREAKERS IN SYSTEM. SWAPPED FIRE TEST RELAYS WITH KNOWN GOOD ONE; NO HELP RETURNED TO ORIGIN. CLEANED CONNECTOR TO FLASHER FIRE BELL RELAY. CHECKED FOR CONTINUITY AT PINS 4 & 6 ON FIRE DETECTION POWER UNIT; NO CONTINUITY AT PINS 4 & 6 ON POWER UNIT; SUSPECT BAD POWER UNIT ORDERED ON REQ. 300082358; P/N 1014A FIRE/OVERHEAT POWER UNIT. ALSO GOING TO ORDER APU ALARM CUTOUT RELAY AS PRECAUTIONARY.)