What was found
DURING CLIMB OUT, PASSING 5000 FT, FLIGHT ATTENDANTS REPORTED VERY STRONG ODOR FROM BACK OF CABIN. NO APU USED ON GROUND. FUMES WENT AWAY AFTER THE NR 2 PACK WAS TURNED OFF. THE NR 2 PACK REMAINED OFF FOR THE DURATION OF FLIGHT. AIRCRAFT WAS GROUNDED. TROUBLESHOT THE CABIN ODOR, AND REPLACED THE APU TO RECTIFIY PROBLEM. PERFORMED A SATISFACTORY OPS CHECK., NO ODOR NOTED.