What was found
VISIBLE SMOKE ERUPTED FROM THE CABIN VENTILATION SYSTEM AT FL 340, APPROXIMATELY 1 HR. INTO FLIGHT. THE AIR SYNOPTIC INDICATED HIGHER THAN NORMAL TEMP IN THE COURIER DUCT. NO OTHER ABNORMAL INDICATIONS OTHER THAN THE ODOR AND THE SMOKE INSPECTED AND REPLACED NR 1, 2, AND 3 COALESER BAGS PER MM 21-54-03-2, COALESER BAGS WERE NOT CONTAMINATED(NO OIL RESIDUE). CHECKED APU LOAD CONTROL VALVE FOR CONTAMINANTS PER MM49-00-00-2, NO CONTAMINANTS. PERFORMED PACK BURNOUT PROCEDURE PER TAFI 21-50-00"V". RAN ALL THREE PACKS PER DC10-10 MM 21-53-01-2 REF EA 8-2150-61080.ALSO RAN ALL THREE PACKS TOGETHER AND SEPERATELY WITH EACH ENGINE. UNABLE TO DUPLICATE THIS CONDITION AS WRITTEN.