As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INFLIGHT THE FIRST OFFICERS STAB TRIM BECAME INOP (MORE DOWN TRIM ONLY) WITH AUTOPILOT ON. THE AUTOPILOT WILL NOT DISENGAGE BY MOVING FIRST OFFICERS TRIM TO NOSE DOWN. REMOVED TRIM SWITCH FROM YOKE (FIRST OFFICERS). SPRAYED CONTACT CLEANER TOP AND BOTTOM OF SWITCH OPS CHECK ONCE OUT OF YOKE OK. OPS THREE TIMES AFTER INSTALL IN YOKE THREE TIMES WITHOUT FAIL.