What was found
ON CLIMBOUT, PASSING 28,500 FT, RECEIVED LT BLEED DUCT WARNING MSG, FOLLOWED QRH, RECEIVED CABIN ALT MSG AND HAD SMOKE IN THE CABIN. O2 MASKS WERE DEPLOYED, DECLARED EMERGENCY, LANDED, AFTER LANDING FIRE DEPT BOARDED AND FOUND SMOKE IN CABIN. ENROUTE, ACFT DIVERTED DUE TO MAINTENANCE. COMPLIED WITH OPS CHECK OF BLEED AIR DETECTION SYS IAW AMM 36-21-00. OPS CHECK GOOD.