What was found
IAD/EWR---CO3411, CREW REPORTED (IN IAD) THAT ON POST FLIGHT (WALKAROUND) ELECTRICAL FAN SMELL IN FORWARD CABIN. MAINTENANCE FOUND FAULTY VENT FAN, AIRCRAFT PLACED ON MEL (CIRCUIT BREAKER PULLED AND TAGGED) IAW MEL 21-70-01 PLACARD NUMBER 012782, AIRCRAFT RETURNED TO SERVICE. ARRIVED IN EWR ON CO3486, EWR MAINTENANCE REMOVED AND REPLACED FORWARD VENT FAN IAW ATR42 AMM 21-26-21. OPS CHECKED GOOD, MEL/PLACARD CLEARED. AIRCRAFT RETURNED TO SERVICE.