As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#2104, BOS-LGW. (ETOPS) (AIRCRAFT PERFORMED AN AIR TURN BACK TO BOS) ' LOUD VIBRATION AND ELECTRICAL SMELL IN THE COCKPIT AND FWD CABIN. ISOLATED IT TO THE BLOWER FAN ONCE THE FAN WAS OFF VIBRATION DISSIPATED. AFTER PARKING WHEN TRYING TO DUPLICATE CB TRIPPED; REMOVED AND REPLACED AEVC BLOWER FAN PER AMM 21-61-51. OPS TESTED AEVC PER AMM 21-61-51 BUT THE FAULT REMAINED. THE ITEM STAYS OPEN. ' (SUPPLEMENTAL TO FOLLOW)