As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED THE NR 1 TRANSFER BUS OFF LIGHT CYCLED DURING FLIGHT RAPIDLY. LOSS OF CAPTAINS FLIGHT INSTRUMENTS: AUTO THROTTLES, FMC, FUEL GAUGES AND OTHERS. CREW DECLARED AN EMERGENCY AND RETURNED TO FIELD AT PHL. FLIGHT LANDED AND TAXIED TO THE GATE WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND GCU IN "G3" POSITION FAULTY. REPLACED GCU PER AMM 24-21-81. OPS TEST GOOD.