As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DEN - ON FLIGHT 2456, THE ESSENTIAL AC CAUTION LIGHT CAME ON IN CRUISE AT 39,000. AUTOMATIC BUS TRANSFER DID NOT TAKE PLACE. RAN CHECKLIST WITH NO CHANGES. TURNED GENERATOR 1 TO OFF, RESET, THEN ON. THEN BUS TRANSFER TOOK PLACE. MAINTENANCE FOUND INTERNAL FAULT OF THE NR 1 IDG. REPLACED NR 1 IDG, AND PERFORMED A OPERATIONAL CHECK OF THE BUS AUTO TRANSFER. OPERATIONAL CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE.