What was found
ETOPS SIGNIFICANT SYS - ATB - L GEN OFF EICAS MSG CAME ON DURING CLIMBOUT. FOLLOWED ELEC-3 PROCEDURES IN QRF ATB. BPCU BITE: DP TRIP L ENG - GEN/FDR MAIN BUS/OVERLAP ZONE. AFTER ACFT ARRIVAL AND BITE CHK COMPLETED, OPERATED ENG AND GEN LOADED. ALL INDICATIONS NORMAL. CHK ALL WIRES BETWEEN LT IDG, GCU AND GEN CONTROL BREAKER FOR SHORTS & OPENS IAW 24-20-00 TABLE 102 NO OPENS OR SHORTS FOUND. IAW TABLE 102 NEED TO REPLACE GCU. R & R GCU IAW AMM 24-22-02 ENG RUN CKS OK ALL INDICATION NORMAL. OK FOR FURTHER SERVICE.