As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FAULT LIGHT ILLUMINATED ON APU START. GROUNDED - YES. ACCOMPLISHED START CONVERTER UNIT SHOWS START SYSTEM INOP-FAULT ISOLATION. VERIFIED MAINT HISTORY MESSAGE 49-41250 REF B737-800 FIM 49-40 TASK 811. REMOVED AND REPLACED APU START CONVERTER UNIT REF B737-800 AMM 49-41-61-000-801 AND 49-41-61-400-801. ACCOMPLISHED 3 GOOD APU STARTS GROUND VERIFICATION CK GOOD NO DEFECTS NOTED. PERFORMED APU BITE CK NO CURRENT FAULTS NOTED REF AMM 49-61-00-700-801.