As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INSPECTION TYPE:N/A**ATB**- **EMERGENCY DECLARED**AFTER TAKEOFF WE LOST L&R UTILITY BUSSES. SHORTLY THERE AFTER, THE "APU GEN OFF" EICAS MESSAGE ILLUMINATED. WE DECLARED AN EMERG AS WE WERE DOWN TO 1 ELECTRICAL SOURCE. RETURNED TO DSMT/S APU GENERATOR SYS. PER FIM TASK 24-20-00-815-801 & 24-20-00-810-805. TRACED TO APU GCU. R&R'D APU GCU IAW AMM 24-22-02. RAN & OPS CK'D GOOD.