What was found
CREW REPORTED A GLD UNSAFE MESSAGE SHORTLY AFTER TAKEOFF. APPROXIMATELY ONE MINUTE AFTER GLD UNSAFE MESSAGE, CREW RECEIVED AN UNSAFE GEAR INDICATION WITH THREE AMBER UP BOXES BLINKING WITH THE HORN. CREW ELECTED TO RETURN TO CLT AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND TROUBLESHOT THE SSCU AND THE PSEU. MAINTENANCE REMOVED AND REPLACED THE PROXIMITY SENSOR ELECTRONIC UNIT IN ACCORDANCE WITH THE AIRCRAFT MAINTENANCE MANUAL. AIRCRAFT WAS RELEASED FOR SERVICE.