As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WITH APU RUNNING & BLEED AIR ON, SMOKE WAS ENTERING CABIN. RAN EACH ENGINE SEPARATELY WITH APU OFF & MECH ONBOARD, CABIN CLEARED & NO SMOKE OR ODOR NOTED. REMOVED AND REPLACED THE APU IAW MM 49-10-00. OPS AND LEAK CHECKED GOOD. RAN APU WITH BLEED AIR ON IN BOTH FULL HOT AND FULL COLD, NO SMOKE PRESENT IN COCKPIT OR CABIN.