What was found
DFW - FLT 1507 - EN ROUTE DFW-YVR, FLIGHT ATTENDANT DETECTED HEAVY SMOKE IN CABIN. DECLARED EMERGENCY. RETURNED DFW, AND LANDED WITHOUT FURTHER INCIDENT. REPLACED APU. REPLACED ACM HEAT EXCHANGERS. REPLACED WATER SEPARATORS BAGS. ACCOMPLISHED PACK BURNOUT PER THE MM. SYSTEM GROUND CHECKED NORMAL OPERATION.