As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ATTEMPTED SEVERAL APU STARTS, APU WOULD NOT FIRE OFF. RECEIVED AN AMBER FAULT LIGHT ON ALL ATTEMPTS. CURRENT STATUS SHOWS MAINTENANCE MESSAGE 49-41251. ACFT GROUNDED. COMPLIED WITH TROUBLESHOOTING IAW FIM 49-40, TASK 812. REPLACED APU START CONVERTER UNIT IAW AMM 49-41-61-000-801 AND 49-41-61-400-801. OPS TESTED GOOD AND CURRENT STATUS BITE SHOWS NO FAULTS IAW AMM 49-61-00-700-801.