As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT, NR 1 GENERATOR FAULTED. PERFORMED PDM PROCEDURE. STARTED THE APU ALL ELECTRICAL POWER WAS LOST REMOVED AND REPLACED LT AND RT GCU IAW AMM 24-23-12. REMOVED AND REPLACED THE APU GCU IAW AMM 24-22-12. RAN ENGINES AND APU, OPS CHECKED GOOD IAW AMM 24-22-00.