What was found
CREW REPORTED, SMOKE IN THE CABIN. A/C RETURNED TO DEN ATBC. CONTRACT MX CHECKED BOTH PACKS, RECIR FAN, LIGHT BALLAST, EYEBALL VENTS, RAN PACKS WITH ENGINES AND APU, PRESSURIZED THE A/C. MX COULDN'T DUPLICATE THE PROBLEM, CREW REFUSED, A/C FLIGHT WAS CANCELLED. STC NR SA3432NM.