What was found
CABIN ODOR ON TAKEOFF IN AFT CABIN, CIRCULATED THROUGHOUT CABIN, WORSE WITH ENG HEAT ON. DID QRH PROCEDURE CAT A. ACCOMPLISHED JC 26L00021001 TROUBLE SHOT CABIN AIR QUALITY, FOUND AVIONICS VENTILATION FILTER CLOGGED. REPLACED FILTER IAW AMM 21-26-43-000-003-A & 21-26-43-400-003-A.