As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, CABIN STARTED FILLING WITH SMOKE. SMOKE WAS ORIGINATING FROM AVIONICS MASTER SWITCH - UNABLE TO TURN SWITCH OFF, SO CIRCUIT BREAKERS WERE PULLED. SMOKE EVACUATION PROCEDURES WERE INITIATED AND SMOKE SUBSIDED. A NORMAL LANDING WAS MADE. PROBLEM CONFIRMED TO BE THE AVIONICS MASTER SWITCH. SWITCH REPLACED WITH NEW. AIRCRAFT RETURNED TO SERVICE.