As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TWO, CONTINUOUS LT & RT YAWING UP TO FL280 LIKE BOTH YAW DAMPERS INOPERATIVE BUT NO EICAS OR LIGHTS. R & R RT YAW DAMP COMPUTER IAW AMM 22-21-04, OPERATIONS CHECKED NORMAL. PERFORMED MCDP TEST 30 IAW AMM 22-00-02, NO FAULTS NOTED, AIRCRAFT REMAINS FULL CAPABILITY.