As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
L AC BUS OFF AT TOP OF CLIMB OUT FROM CVG BOUND FOR MHT. CREW RAN THROUGH THE QRH AND RESET EVERYTHNING. THEY DECLARED AN EMERGENCY (EDC) AND RETURNED TO CVG WITHOUT INCIDENT. (ATB). MAINTENANCE REMOVED AND REPLACED GCU IAW AMM 24-22-02. OPS CHECK GOOD AC REMAINS ETOPS 180. AIRCRAFT RETURNED TO SERVICE.