As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLIGHT CREW PREFLIGHT WHILE OPERATING THE ALTERNATE STABILIZER TRIM SWITCHES, A POP AND A FLASH OCCURRED WITH A SMALL FIRE BELOW TRIM SWITCHES UNDER PEDESTAL, FIRST OFFICER BLEW FIRE OUT. C/B D-10 POPPED. REPLACED ALTERNATE TRIM BRAKE RELEASE SWITCH S10-8. FOUND THAT SWITCH SPARKED IGNITING DUST IN PEDESTAL. NO DAMAGE RESULTED DUE TO SMALL FIRE.