What was found
ALB/IAD - FLT 6255 - DURING APPROACH FLIGHT AT 1120 HOURS ON 8-27-96, ABORTED APPROACH DUE TO LANDING GEAR WARNING HORN SOUNDED WITH GEAR DOWN AND FLAPS SELECTED TO 20 DEGREES. MAINTENANCE TROUBLESHOT AND INSPECTED LANDING GEAR WITH NO FAULTS FOUND. REMOVED AND REPLACED THE ACTUATOR, LOCK VALVE, EMERGENCY RELIEF VALVE, SELECTOR VALVE, WARNING HORN, AND UNLOCK LIGHT. ALL SYSTEMS FUNCTIONED PROPERLY IAW MM. MAINTENANCE THEN RELEASED THE AIRCRAFT FOR SERVICE. REF: OPERATOR CONTROL NRS VTZA96343, 96ZZZX5166, 96ZZZX5167, 96ZZZX5168, AND 96ZZZX5170.