What was found
DFW - FLT 853 - AFTER TAKEOFF DFW WHEN LANDING GEAR HANDLE RAISED, THREE RED LIGHTS ILLUMINATED WITH NO YELLOW GEAR DOOR LIGHT. SELECTED LANDING GEAR DOWN AND GOT THREE GREEN INDICATION. AIRCRAFT RETURNED TO DFW AND LANDED WITHOUT INCIDENT. REPLACED LANDING GEAR PROXIMITY SWITCH UNIT. ACCOMPLISHED LANDING GEAR RETRACTION CHECK WITH NO DEFECTS FOUND. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)