ON 12-13-00 AT 6:00 AM WHILE ATTEMPTING TO LOWER THE CREW, THE JEWELL CHIPPY HOIST ROLLED BACK. THE HOIST WAS TAKEN OUT OF SERVICE. EXTENSIVE TESTS WERE PERFORMED WITHOUT FINDING THE CAUSE AND A FIELD ENGINEER FROM GE INDUSTRIAL SYSTEMS WASCALLED AND ARRIVED ON 12-14-00. A VRG RELAY WAS REPLACED AND EXTENSIVE CHECKS WERE MADE BEFORE PLACING HOIST BACK IN OPERATION ON 12-15-00.