What was found
IN CRUISE FLIGHT AT 41,000 FEET, FMS 1 COURSE STARTED WONDERING. WHEN CREW LOOKED DOWN, FMS 1 WAS OFF. (WHEN FMS 1 CAME BACK ON A FEW SECONDS LATER, IT SHOWED "CUSTOM DATABASE INVALID MSG). FMS 1 WENT OUT AGAIN AND BACK ON AND AT THAT POINT THE CREW SMELLED ELECTRIC SMOKE SMELL. AFTER DOING THE CHECKLIST, CREW DECIDED TO SHUT #1 FMS/RADIO OFF AND LAND. MAINTENANCE THOROUGHLY CHECKED #1 FMS SYSTEM, WIRING, AND OPERATION WITH NO DEFECTS, HOWEVER THEY NOTED A BURNT SMELL AT THE BACK OF THE #1 FMS CDU. REPLACED #1 FMS CDU WITH NO DEFECTS NOTED.