As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW REPORTED UNCOMMANDED RUDDER MOVEMENTS ON CLIMB, AT LEAST SIX TIMES, ON BOTH AUTO PILOTS 1 AND 2, IN LEVEL FLIGHT AND TURNS. DECLARED AN EMERGENCY AND RETURNED TO BOS. REMOVED AND REPLACED BOTH LEFT AND RIGHT FLIGHT AUGMENTATION COMPUTERS AND BOTH AILERON/ELEVATOR COMPUTERS. PER VENDOR TEARDOWN REPORT, THE NR 2 ELAC FAILED PT 4 OF TEST STEP 180824 FUNCTION: 'CONVERT DC INPUTS AN14/COM' DURING STRESS TESTING. REPLACED SEVERAL RESISTORS ON CAN CARD.