As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PDX - DURING CRUISE FLIGHT CREW NOTICED ACRID/PLASTIC BURNING ODOR AND SMOKE IN COCKPIT. NO SMOKE OR ODOR IN CABIN. DECLARED EMERGENCY AND RETURNED TO FIELD. SMOKE/HAZE NOTICED IN VICINITY OF HUD COMBINER. ELECTED NOT TO TURN-OFF ANY GENERATOR SWITCHES DUE TO PROXIMITY OF AIRPORT. REPLACED PILOTS WINDSHIELD. OPERATIONAL CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.