As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON AIRCRAFT TEST FLIGHT FOR COMPLETION OF TAWS INSTALLATION. AIRCRAFT EXPERIENCED SMOKE IN THE CABIN AND COCKPIT. CREW DECLARED AND EMERGENCY LANDING AND PERFORMED AN UNEVENTFUL LANDING, USING NORMAL PUBLISHED EMERGENCY PROCEDURE. TROUBLESHOOTING FOUND THE APU GCU BURNED OUT (4) DIODE BOARD GCU REPLACED WITH AN OVERHAULED UNIT AND OPS CHECKED OK. (K)