As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED TO FIELD DUE TO SMOKE IN COCKPIT. FLT CREW REPORTED THAT CAPTAIN'S ELECTRONIC HORIZONTAL SITUATION INDICATOR (EHSI) WENT BLANK DURING THE INCIDENT. CAPTAIN'S EHSI WAS REPLACED. SHOP DETERMINED THAT THE REMOVED EHSI HAD A FAILED CAPACITOR C116 ON CARD A5A1. THE CAPACITOR HAS SIGNS OF OVERHEATING AND LIKELY CAUSED THE SMOKE IN THE COCKPIT.