What was found
CREW REPORTED, ON CLIMB OUT, CABIN BECAME FILLED WITH SULFURIC / ELECTRICAL BURNING ODOR. CREW ELECTED TO REMAIN IN PATTERN AND RETURNED TO BASE, LANDING WITHOUT INCIDENT. PILOT REPORTED THAT ODOR MAY HAVE EMINATED FROM REAR OF ACFT. MX INSPECTED ACFT. COULD NOT DUPLICATE ODOR IN CABIN. INSPECTED AUTO PILOT SYS. CLEANED ALL CONNECTION AT TRIM AND PITCH SERVOS. NO DEFECTS FOUND. AS A PRECAUTIONARY MEASURE, MX INSPECTED CABIN VENT SYS FAN, NO DEFECTS NOTED ALSO. ACFT RELEASED BACK TO SERVICE.