What was found
AIRCRAFT RETURNED, (FIRE DETECTOR LOOP A), (APU FIRE) AND (LT CSD HIGH TEMPERATURE) LIGHTS TURNED ON, AUDIBLE ALARM WAS ACTIVATED, LT GENERATOR WAS INOPERATIVE AND CAPTAIN ACTIVATED FIRE EXTINGUISHER BOTTLES. AIRCRAFT WAS SENT TO THE HANGAR AND FIRE DETECTION SYSTEM WAS CHECKED DETECTING DETECTORS A AND B TERMINALS WITH EXCESIVE OIL AND DIRTY. CLEANING AND TEST WERE PERFORMED IAW MM 26-10-00, ALL CORRECT. DURING OVERNIGHT CHECK AND AS A PRECAUTIONARY ACTION, THE DETECTOR D1-6 OF LOOP A AND CONNECTORS P1-755 AND P1-751, WERE REPLACED IAW MM 26-10-00 AND 26-12-00, TESTED CORRECT.