What was found
ENROUTE, PILOT BEGAN TO DETECT SMOKE. RETURNED TO DEPARTURE. DURING RETURN, PILOT SHUTDOWN ELECTRICAL SYS & LANDED WITHOUT INCIDENT. AFTER ELECTRICAL SYS WAS SHUTDOWN, PILOT NOTICED A DECREASE IN THE ODOR OF SMOKE. MX DISCOVERED THE LEFT INTERIOR VENT FAN HAD SEIZED BEARINGS. SEIZED BEARINGS CAUSED THE MOTOR'S WINDINGS TO HEAT UP. MX FOUND NO EXTERNAL CHARRING OR DISCOLORATION TO THE MOTOR OR ANY ADJACENT EQUIPMENT OR STRUCTURE. NO SMOKE DAMAGE TO THE INTERIOR OF ACFT, AND THERE WAS NO EXTERNAL WIRING DAMAGE. VENT FAN ASSY WAS REPLACED AND ACFT RETURNED TO SERVICE.