As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOS - FLT 121 - EN ROUTE LGW-BOS - DURING CRUISE, THE TRANSFORMER AT SEAT 29G SHORTED OUT CAUSING SPARKS AND SMOKE. ALL VIDEOS IN ZONE WERE BLANK. SECURED SYSTEM. LANDED BOS WITHOUT INCIDENT. REPLACED WIRING HARNESS AT SEAT 29G. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)