What was found
PHL FLT 750 EN ROUTE PHL TO BRU. DURING CRUISE FLIGHT, JUST PRIOR TO ETOPS, THE ACFT LOST ALL POWER TO THE LT ACFT BUS. ALSO, THE APU FAULT LIGHT CAME ON WITH EICAS MSG APU FAULT. THE CREW PERFORMED THE APPROPRIATE RESETS & THE ACFT POWER RETURNED. THE CREW DECIDED TO RETURN TO PHL AS A PRECAUTIONARY. THE FLIGHT LANDED IN PHL WITHOUT FURTHER INCIDENT. REPLACED CB DC BUS L SECT 2 P6-2 D8 & REPAIRED WIRES W5302-203B-18, 203R-18, & W5302-001-18 APPROX SIX INCHES DOWN FROM IDG CONNECTOR D10964.