As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
YAW DAMPER INDUCED YAW MOVEMENT FROM TAKEOFF UNTIL YAW DAMPER TURNED OFF, OSCILLATIONS GOT WORSE WITH AIRSPEED INCREASE. *S/D* REMOVED PCU. BENCH TEST OF THE PCU REVEALED THAT IT FAILED THE PHASE LAG TEST PER BOEING OHM 27-20-01. THE TRANSFER VALVE WAS REPLACED AND THE PCU PASSED ALL TESTS. AIRCRAFT HAS HAD NOT OSCILLATIONS SINCE REPLACEMENT OF THE PCU.