What was found
WHILE ENROUTE TO ECP, CAPTAIN STATED THAT THE COCKPIT WENT DARK AND WHEN THE LIGHTS CAME BACK ON THEY HAD AN AC ESS BUS FAIL MESSAGE. CREW FOLLOWED THE QRH WITH NO VALID RESULTS. DECIDED TO RETURN TO CLT. CAPTAIN DID DECLARE GOING BACK AND THEN CANCELED THE EMERGENCY ONCE HE GOT ON RAMP RADIO. TRUCKS WERE NOT ROLLED. FLIGHT IS SWAPPING TO AIRCRAFT J01 AND GOING TO CONTINUE TO ECP. AC ESS BUS AMBER MSG IN FLT / REMOVED AND REPLACED IDG GCU #1 IAW CRJ 900 AMM 24-11-07-000/400-801. OPS CHECK GOOD. NO OTHER DEFECTS NOTED."