What was found
AT 35,000 FEET, MASTER WARNING AND CABIN ALT LIGHTS ILLUMINATED WITH CABIN CLIMBING AT 1000 FT PER MINUTE AND ALL PASSENGER OXYGEN MASKS DEPLOYED. FOLLOWED COM PROCEDURES AND WERE UNABLE TO CONTROL CABIN IN AUTO OR MANUAL WITH AIRFOIL AND ENGINE ANTI-ICE OFF. DESCENDED TO 10,000 FT AND RETURNED TO MSP. MAINTENANCE FOUND A BLOWN DUCT BOOT AND BROKEN CLAMP AFT OF RIGHT WATER SEPARATOR. REPLACED BOOT AND CLAMPS. OPERATIONAL AND PRESSURIZATION CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.