EMER DECLARED BY MLG WHEN CABIN PRESSURE CTL IS LOST.

Narrative

AFTER LEVEL-OFF AT CRUISE ALT OF FL330; THROTTLES RETARDED FOR MACH CRUISE; SIMULTANEOUSLY CABIN BEGAN MAJOR EXCURSIONS (PLUS/MINUS 2000 FPM). A DSCNT WAS REQUESTED AND NORMAL DSCNT RATE STARTED (TO FL270). CABIN CONTINUED A SLOW CLB AND IT BECAME OBVIOUS THAT CABIN WOULD SOON PAS 10000 FT; EMER DECLARED; AND RAPID DSCNT BEGUN. UNABLE TO CTL CABIN (STOP THE CABIN FROM CLBING) IN MANUAL PRESSURIZATION AS CABIN CONTINUED TO CLB. CABIN REACHED 13000 FT. WE MANUALLY DEPLOYED OXYGEN MASKS FOR PAX AND FLT ATTENDANTS. FLT DSNDED TO MINIMUM ENRTE ALT OF 13000 AND DIVERTED TO SLC. NORMAL LNDG WAS MADE. NO PAX HURT OR INJURED. MAINT PERSONNEL DISCOVERED THAT THE 'SECOND' CABIN CTLR HAD FAILED (THE ACFT HAS 2 IDENTICAL CTLRS -- THE OTHER CTLR HAD BEEN MEL'ED 6 DAYS AGO). THE MANUAL CTLR FAILED TO OPERATE PROPERLY BECAUSE SOME DUCT INSULATION HAD JAMMED IN THE DUMP VALVE ALSO (UNKNOWN IF IT WAS JAMMED BEFORE; OR BECAUSE OF THE OTHER SECOND CTLR FAILURE). THE ACFT IS ROTATED THROUGH MAJOR OVERNIGHT MAINT ONLY ONCE IN EVERY 7 DAYS AND WAS SCHEDULED FOR REPAIR TO MEL'ED CTLR ON THE FOLLOWING DAY -- 1 DAY AFTER MY PROB!