As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHIP 3811 -ATB/DE- RETURNED TO BOS DUE TO RT PACK FAILURE AND PRESSURIZATION LOSS WITH LT PACK ON MEL. CORRECTIVE ACTION: REPLACED RT ENG HIGH STAGE REGULATOR AND LT PACK ACM. REPLACED RT RAM AIR EXIT DOOR ACTUATOR AS PRECAUTION. PACK OPS CK GOOD.