As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AT FL340, EXPERIENCED SMOKE IN COCKPIT FROM "FL' BUTTON ON TRANSPONDER AND FOUND "ELECTRICAL PANEL LIGHTS" CIRCUIT BREAKER POPPED; FLIGHT DIVERTED TO ORD AND LANDED WITHOUT FURTHER INCIDENT. REPLACED AIR TRAFFIC CONTROL CONTROL PANEL IAW AMM 34-53-03, OPS CHECK GOOD.