What was found
AFTER DEPARTING MIA WHILE CLEANING UP AIRCRAFT STAB CRUISE TRIM CIRCUIT BREAKER POPPED. CLIMBING THROUGH 17500 IT WAS DISCOVERED AIRCRAFT COULD NOT BE TRIMMED DOWN BELOW 0. REVIEWED QRH FOR GUIDANCE AND CONTACTED GOC AND MOCC FOR SUGGESTIONS. DECISION WAS MADE TO RETURN TO MIA BECAUSE OF AIRSPEED/ALTITUDE RESTRICTIONS, MODERATE TURBULENCE EN ROUTE AND UNCERTAINTY OF AIRCRAFT MALFUNCTION. REMOVED AND REPLACED AUTO PILOT STAB TRIM SERVO MOTOR PER MM 22-11-021-2, OPS CKS GOOD ON GROUND PER MM 22-11-021-2.