What was found
DURING CLIMB OUT AT 600 FEET L GEN OFF ILLUMINATED. RAN QRH AND ABLE TO RESET L GEN. STARTED APU FOR BACKUP AND APU RAN FOR ABOUT 5 MINUTES AND GOT AN APU FAULT EICAS AND APU SHUTDOWN. DURING DESCENT L GEN OFF EICAS ILLUMINATED AGAIN. QRH ONLY ALLOWS ONE RESET PER FLIGHT. DECLARED EMERGENCY AND LANDED AT DESTINATION. DECIDED TO TRY APU AGAIN SINCE FAULT LIGHT EXTINGUISHED BUT APU ONLY RAN FOR 3 MINUTES AND FAILED AGAIN. REMOVED AND REPLACED L/H ENGNE IDG USING B757 MM 24-11-01-4, LEAK CHECK GOOD, OPS CHECKED GOOD.