What was found
DURING CLIMB OUT, AUTOPILOT WAS ENGAGED. WITHIN 10 SECONDS, AUTOPILOT ROLL TRIM ANNUNCIATOR ILLUMINATED. AUTOPILOT WAS COMMANDED TO DISENGAGE. PILOT REPORTED THAT ALL AXIS EXCEPT THE ROLL FELT FREE. THE AILERONS STILL FELT AS IF THE AUTOPILOT ROLL SERVO REMAINED ENGAGED. THE AIRCRAFT RETURNED BACK TO THE AIRPORT AND LANDED WITHOUT ANY ISSUE. DURING TROUBLESHOOTING, WE COULD NOT DUPLICATE THE ISSUE USING NORMAL TESTING PROCEDURES. WE THEN ENGAGED THE AUTOPILOT AND HELD ONTO THE AILERON TO SIMULATE AN AIR LOAD AND THEN COMMANDED THE AUTOPILOT TO MAKE A TURN. WE THEN RECEIVED THE SAME TRIM ANNUNCIATION. THE SERVO WAS REPLACED, AND THE PROBLEM COULD NOT BE DUPLICATED. AIRCRAFT PERFORMED AN OPERATIONAL FLIGHT CHECK AND WAS RETURNED TO SERVICE.