What was found
AIRCRAFT WAS GROUNDED: WHILE OPERATING THE AIRCRAFT WITH THE APU INOPERATIVE AND ON MEL, THERE IS AN OCCASIONAL MILD TO VERY OCCASIONALLY MODERATE DIRTY-SOCK SMELL COMING FROM THE PACKS. THEREFORE IT SEEMS PLAUSIBLE THAT THE SOURCE OF THE RECENT SOF EVENT MAY BE RELATED TO THE PACKS AS OPPOSED TO THE APU. THE ODOR IS INTERMITTENT. MAINTENANCE REPLACED THE APU PER TASK CARD 26L31049003, MAINTENANCE ACCOMPLISHED THE DECONTAMINATION OF THE ENVIRONMENTAL CONTROL SYSTEM AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK.