What was found
FOR FLIGHT 3832 WHILE AT THE GATE A SMOKE AFT LAVATORY WARNING MESSAGE CAME ON. THE FLIGHT ATTENDANT DISCHARGED A HALON FIRE EXTINGUISHER. NO SMOKE OR FLAMES WERE NOTICED, HOWEVER NOTICED A SLIGHT ODOR IN CABIN. THE AIRCRAFT WAS REMOVED FROM SERVICE. FOUND ODOR TO BE COMING FROM BALLAST ABOVE SEAT 14C. REMOVED AND REPLACED BALLAST IAW CRJ AMM 33-21-03 . THE OPERATIONAL CHECK WAS GOOD NO OTHER DEFECTS NOTED. REMOVED AND REPLACED THE FLIGHT ATTENDANT PORTABLE FIRE EXTINGUISHER AS REQUIRED. THE AIRCRAFT WAS RETURNED TO SERVICE.