What was found
DURING CRUISE, JUST PRIOR TO INITIAL DESCENT AT APPROX 37,000 FT, CREW RECEIVED MACH TRIM CAUTION MSG AND A STAB TRIM CAUTION. QRH WAS COMPLIED WITH FOR BOTH MESSAGES WITH NO CORRECTION. SHORTLY THEREAFTER, CREW RECEIVED AUTOPILOT TRIM CAUTION MSG AND COMPLIED WITH QRH WITH NO CORRECTION. CREW DECLARED EMERGENCY AND ELECTED TO PERFORM NO FLAP LANDING DUE TO HEAVY CONTROL FORCES WITH NOSE DOWN. AIRCRAFT LANDED SAFELY. REMOVED AND REPLACED HORIZONTAL STAB TRIM MOTOR CONTROL UNIT (MCU). OPS CHECK GOOD. AIRCRAFT OK FOR SERVICE. (K)