What was found
FUMES AT AFT CABIN (ROWS 25-30) LEFT. ODOR INTERMITTENT, OCCURING ROUGHLY EVERY 10 MINUTES. THE AIRCRAFT WAS GROUNDED. TROUBLESHOT IAW CAR 33L00021001, FOUND NO ODOR COMING FROM ENGINE BLEED OR PACK SYSTEM. DID FIND FAULTY LIGHT BALLAST AT ROW 30 CEILING. REPLACED BALLAST, OPS GOOD.