What was found
(CAN) AFTER SELECTING GEAR UP, LT AND RT MAIN GEAR DOOR AMBER WARNING AND NLG RED WARNING. GEAR SELECTED DOWN AND NORMAL EXTENSION, AFTER GEAR DOWN (AMBER) NLG LIGHT REMAINED ILLUMINATED. MAINT INSPECTION/ TROUBLE SHOOTING REPLACED LANDING GEAR SELECTOR VALVE AND NLG DOOR SEQUENCE VALVE, DURING GEAR SWINGS GEAR FAILED TO RETRACT AFTER SECOND CYCLING . FURTHER INVESTIGATION FOUND NLG DOOR SEQUENCE VALVE GROUND STUD (WIRE DIAGRAM 32-30-00 SHEET 4 OF 4 PAGE 1 WIRE IDENTIFIER 93A22N , STUD IDENTIFIER 3251-GS-1) LOOSE. STUD LOCATED ON BULKHEAD FWD OF FWD PRESSURE BULKHEAD. STUD TIGHTENED, GEAR SWINGS COMPLETED SUCCESSFULLY. AC RETURNED TO SERVICE. (TC NR 20071220001)