As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT REPORTED THAT DURING THE BOARDING PROCESS. A HEAVY SMOKE SMELL FROM THE MAIN CABIN CB PANEL WAS EMANATING THROUGH THE COCKPIT. THE CREW WRE UNABLE TO PINPOINT THE SOURCE. THE AIRCARAFT WAS SHUTDOWN AND THE PASSENGERS WERE DEPLANED WITHOUT INCIDENT. MAINTENANCE REPLACED THE COCKPIT GENERATOR CONTROL UNIT, SYSTEM CHECKED SERVICEABLE AND REPLACED THE AC BUS CONTACTOR.