What was found
DURING CLIMBOUT, A STABILIZER TRIM FAILURE WAS EXPERIENCED FOLLOWED BY MACH TRIM FAILURE AND AUTO PILOT TRIP FUNCTION INOPERATIVE. THE CAPTAIN REPORTED THAT THE FORCES ON THE CONTROLS WERE MANAGEABLE. CREW COMPLIED WITH THE QRH TO RESET THE SYSTEM, BUT THE ATTEMPT WAS UNSUCCESSFUL. EMERGENCY EQUIPMENT WAS REQUESTED TO STANDBY AS A PRECAUTION, AND A SAFE LANDING WAS PERFORMED. MAINTENANCE REMOVED AND REPLACED THE STABILIZER TRIM MOTOR CONTROL UNIT. OPERATIONAL CHECKS, GOOD. AIRCRAFT RETURNED TO SERVICE.