What was found
AIR TURN BACK, WHILE ENROUTE, EICAS MSG GND EQUIPMENT COOLING RAN QRH AND PUT GND EQUIPMENT IN ALT. PROBE HEAT EICAS MSG. RT FWD FUEL PUMP AND L AFT FUEL PUMP EICAS MSGS. STATUS MSG EQPT COOLING FAN. RESET CB 310 AND RAN ALL SYSTEMS COMING OF AC BUS L SECTION 3 SIMULTANEOUSLY AND BREAKER DID NOT TRIP, REF WD 24-51-13-1. REPLACED CB C310 PRECAUTIONARILY. AFFECTED SYSTEMS OPS CHECK NORMAL PER MM 28-22-00, 30-31-00, 30-32-00, AND 21-58-00.