As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNEXPLAINED YAW FELT BY CREW ON FLIGHT DECK. YAW DAMPER COUPLER BITE TEST WAS PERFORMED BUT NO FAILURES WERE FOUND. REPLACED THE YAW DAMPER COUPLER PER MM 22-12-31 AS PRECAUTION. A BENCH TEST ON THE REPLACED COUPLER DETERMINED THAT THE TRANSISTOR (Q11) IN THE OUTPUT VOLTAGE CIRCUIT WAS BAD. OPS CHECK OK.