What was found
AC BUSS 3 OFF LEVEL 1. BUSS DID NOT FAIL UNTIL MULTIPLE ITEMS ON BUSS FAILED OVER A PERIOD OF ABOUT 7 MINUTES. FIRST OIL PRESS 3, THEN ICE DET SINGLE, THEN FO RA, THEN TANK 1 PUMPS LO, THEN AUTO SLAT FAIL, THEN AUTOTHROTTLES FAILED, THEN NO AUTOLAND, THEN AC BUSS ACTUALLY FAILED WITH THE BUSS AC 3 OFF ALERT. PERFORMED FIM 24-20-12, REMOVED AND REPLACED NR 3 GCU IAW AMM 24-21-03, RAN ALL 3 ENGINES PER JRH FOR 10 MINS NO DEFECT NOTED ALL ITEM WORKED AND NO AC BUS 3 LIGHT NO MESSAGES.