What was found
IN FLIGHT L GEN OFF AND ASSOCIATED EICAS. L AC BUS OFF. RESET IN FLIGHT. OPERATED NORMALLY FOR 20 MINUTES. SAME MALFUNCTION AGAIN DURING DESCENT. EMERGENCY DECLARED. BITE CHECKED BPCU PER FIM 24-20 F/T 801. FOUND SAME MESSAGES AS PREVIOUS L GEN SYSTEM DP TRIP AND MAIN BUS/OVERLAP ZONE ON LAST FLT FAULT HISTORY. VERIFIED ELEC CONNECTIONS ON LT IDG ARE TIGHT & GCU PINS ARE SECURE. RESET LT AC BUS RAN BOTH ENGS & GENERATOR, OPS NORMAL. CYCLED LT & RT GEN SWITCHES. COULD NOT DUPLICATE. PERFORMED ALL WIRING CHECKS PER TSI 24-10/2691 STEPS 1 & 2, ALL WIRING CHECKS GOOD, R & R LT IDG PER STEP 3 ON TSI, OPS CHECKED GOOD.