As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOTS REPORTED DURING BOARDING PROCESS A HEAVY SMOKE SMELL FROM THE MAIN CB PANEL EMANATING THROUGHOUT THE COCKPIT. CREW UNABLE TO PINPOINT SOURCE. A/C SHUT DOWN AND PASSENGERS DEPLANED. REPLACED COCKPIT GCU AND AC BUS CONTACTOR.