As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER LANDING, CREW REPORTED SMOKE STARTED COMING IN CABIN AND FLIGHT DECK WHEN APU WAS STARTED AND PACKS WERE TRANSFERRED. DECLARED EMERGENCY AND COMPLIED CHECKLIST. MAINTENANCE TROUBLESHOT, R & R APU ASSY AND PERFORMED CHECKS IAW AMM. ACFT RELEASED FOR SERVICE.