As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WOULD NOT SHUT OFF. SUSPECTED WELDED APU CONTACTOR. CREW NOTICED EXCESSIVE SMOKE FROM APU AND PULLED THE APU FIRE BOTTLE. R & R THE APU GENERATOR IAW CARD 24-30-02. R & R APU START CONTACTOR IAW STANDARD PRACTICES AND APU GCU IAW AMM 24-49-03 AS PRECAUTION. RAN AND SHUT DOWN APU SEVERAL TIMES WITH NO FAULTS.