As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FIRST ATTEMPTED APU START AT FL 400. APU START FAILED ON FIRST ATTEMPT WITH FAULT LIGHT. QRH FAULT LIGHT EXTINGUISHED AFTER 5 MINUTES. DESCENDING TO FL 340 FOR 2ND ATTEMPT, APU START SUCCESSFUL AT FL 340. ACFT GROUNDED. R & R APU START POWER UNIT AND START CONVERTER UNIT IAW AMM REF'S 49-41-71-801/49-41-71-400-801 AND 49-41-61-000-801/49-41-61-400-801. OPS CK GOOD.