What was found
UPON GEAR RETRACTION AFTER TAKEOFF, THREE GREEN GEAR LIGHTS LIT UP SIMULTANEOUSLY WITH THREE RED UNLOCK LIGHTS ON BOTH OVERHEAD PANEL, AND, MAIN INSTRUMENT PANEL, AND, THE GEAR WOULD NOT RETRACT. MAINTENANCE REMOVED, AND,REPLACED THE LANDING GEAR CONTROL VALVE, PERFORMED A OPERATIONAL CHECK, NO DEFECTS NOTED, AND, THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.