As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON GROUND STARTED APU NORMAL INDICATIONS BUT NO BLUE LIGHT APU GEN OFF BUS AND WOULD NOT ACCEPT LOAD. ONCE ENGINES SHUT DOWN, IT ACCEPTED LOAD WITH BLUE LT ON. THEN EXTINGUISHED, OPS NORMAL. GROUNDED - YES. APU GENERATOR SYSTEM IS INOP. GCU SHOWS NO FAULTS DURING BITE TEST REF FIM 24-21 TASK 801. ACCOMP APU START WITH EXTERNAL PWR & SWITCH CHECK, CHECK PASS REF AMM 24-21-00-860-011.