As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU POWERING ACFT. GROUND POWER CONNECTED AND SELECTED. ALL POWER DISCONNECTS FROM BUSSES. APU WILL STILL CONNECT BUT GROUND POWER DESELECTS APU AND DOES NOT CONNECT POWER TO THE ACFT. ACFT GROUNDED. AMM 24-21-41, REMOVED/REPLACED C803 AUX PWR BREAKER, OPS NML REF SAME AMM. CYCLED APU BUS TO EXT PWR BUSSES BACK AND FORTH NUMEROUS TIMES WITH NO DISCREPANCIES.