What was found
MCI - FLT 301 - AIR RETURN, NO EMERGENCY DECLARED, LANDING UNEVENTFUL. AT APPROXIMATELY 1,000 FEET AGL, MASTER CAUTION LIGHT CAME ON, EQUIPMENT DOOR LIGHT CAME ON, AND UNABLE TO PRESSURIZE. SECURED E/E DOOR CLOSED. DEFERRED MEL 52-3 C1 NR M005564 PER MAINTENANCE CONTROL 'EQUIP' LIGHT SOCKET BAD. REPLACED DOOR WARNING LIGHT MODULE PER MM 52-71-0, OPS CHECK NORMAL. THIS CLEARS DEFERRAL M005564. (X)