As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, SMOKE WAS OBSERVED FROM FLIGHT ATTENDANT CALL BOX. FLIGHT CREW DISCHARGED TWO CHEMICAL FIRE EXTINGUISHERS AND PULLED SYSTEM CIRCUIT BREAKERS. AIRCRAFT CONTINUED TO LGW AND LANDED WITHOUT INCIDENT. MAINTENANCE REPLACED SIDEWALL TRANSFORMER AND FIRE EXTINGUISHERS. OPERATIONAL CHECK GOOD.