As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STAB TRIM AND MACH TRIM DISENGAGES WHEN TRIM NOSE UP OR NOSE DOWN TRIM SWITCH IS ACTIVATED. STAB TRIM AND MACH TRIM DISENGAGED AFTER T/O WHEN ACTIVATING TRIM SWITCH. AIR RETURN TO ROC. REPLACED HORIZONTAL STAB TRIM CONTROL UNIT WITH SERVICABLE UNIT IAWAMM 27-41-01, OPS CK GOOD. PERFORMED OPS CK OF HORT STAB CONTROL AND MACH TRIM IAW AMM 27-41-00, OPS CK GOOD AT THIS TIME AND NO FAULTS.