As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMBOUT AT 12,000 FEET, A LOUD POP WAS HEARD FOLLOWED BY SMOKE COMING FROM OVERHEAD OF COCKPIT JUMPSEAT AT OXYGEN CONTROL PANEL. FLIGHT CREW DECLARED AN EMERGENCY AND THE AIRCRAFT WAS RETURNED TO DLH. LANDING WAS UNEVENTFUL. MAINTENANCE FOUND OBSERVER'S OXYGEN CONTROL PANEL LIGHT PLATE OVERHEATED. REPLACED PANEL, OPERATIONAL CHECK NORMAL.