As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED TO START ON THE FIRST TRY. APU FAIL LIGHT ILLUMINATED. RAMP REPORTS LOTS OF SMOKE FROM THE APU EXHAUST AFTER FAILURE TO START. PLACED APU ON MEL 49-00-1. CLEARED BY: LOOKING AT CDS AND FOUND FAULT CODE 129-1 EGT T/C 2 OPEN. C/W FIM Q400 49-70-070810-810. FOUND NO DEFECTS WITH THE WIRING. REPLACED THE THERMOCOUPLE NR 2 IAW 49-70-07-000-801 AND TASK 49-70-07-400-801. OPS CHECKS GOOD. CLEARED MEL.