What was found
CREW REPORTED STAB CHANNEL ONE INOPERATIVE MESSAGE DURING FLIGHT. ENGAGED SYSTEM AND BOTH STAB TRIM AND MACH TRIM WENT INOPERATIVE. CREW FOLLOWED QRH TO RE-ENGAGE SYSTEMS. STABILIZER CHANNEL, 1 INOPERATIVE MESSAGE OCCURRED AGAIN, FOLLOWED BY STAB TRIM AND MACH TRIM OFF AND THEN AUTOPILOT NOSE UP MESSAGE. CREW FOLLOWED QRH TO DISCONNECT AUTOPILOT. CREW ENGAGED ALL SYSTEMS EXCEPT STAB TRIM ONE, RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED, R & R HORIZONTAL STABILIZER MOTOR CONTROL UNIT (MCU) AND PERFORMED CHECKS IAW AMM. OPS CHECK FLIGHT (OCF) PERFORMED SATISFACTORILY. ACFT RELEASED FOR SERVICE.