What was found
AT GATE, PRIOR TO DEPARTURE, FLT 362 ORD-CVG, THE LT OVERWING EXIT EMERGENCY LIGHTING WAS INOPERATIVE. MAINTENANCE REPLACED THE LT OVERWING (EPSU) EMERGENCY POWER SUPPLY UNIT (11WL), IAW AMM 33-51-38PB401 & OP'S CK'D OK. AIRCRAFT WAS RETURNED TO SERVICE.