As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STATUS MESSAGE FOR STBY BUS APU. CMC FOUND MESSAGE 24727 IAW FIM 24-60 TASK 809, REV 90 FOR TROUBLESHOOTING, J4 TO BCU2 WIRING CHECKED NORMAL. SWAPPED BCU 1 AND BCU 2 AND FOUND BCU 2 FUNCTION BAD. REPLACED THE BCU-2 IAW AMM 24-23-01, REV 90. PERFORMED EPGS (BCU2) GROUND TEST PASSED AND STANDBY POWER TESTED NORMAL.