As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WILL NOT START, MAINT MESSAGE 49-41245 "APU START CONVERTER UNIT SHOWS UNDERVOLTAGE". NOTE: SCU CAN BE HEARD NORMALLY FOR APPROX 10 SECONDS UNTIL "NO ROTATION SHUTDOWN" OCCURS AND ASSOCIATED MAINT MESSAGE 49-41042. GROUNDED - YES. REMOVED AND REPLACED IGNITION EXCITER UNIT PER B737-800 AMM 49-41-31, OPS CHECKS GOOD.