As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 421 - BED - PRIOR TO DEPARTURE FLIGHT CREW NOTED SMOKE ON FLIGHT DECK. FOUND SUSPECT EVIDENCE OF NR 2 BUS TIE BREAKER OVERHEAT WITH SUBSEQUENT DAMAGE TO ELECTRICAL SHELF. REMOVED AND REPLACED ELECTRICAL SHELF AND NR 2 BUS TIE BREAKER. NR 2 BUS TIE BREAKER, VOLTAGE REGULATOR, AND BUS PROTECTION PANEL REPLACED AS PRECAUTION DUE TO SMOKE RESIDUE FROM FAILED BUS TIE BREAKER. (M)