A B737-300 FLT CREW LOST CONTROL OF CABIN PRESSURE AND GOT A CABIN ALT WARNING HORN. THEY RECEIVED A LOWER ALT AND WERE ABLE TO CONTROL THE CABIN PRESSURE WITH THE STBY CONTROLLER.

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OUR CRUISE ALT WAS FL370. WE RECEIVED DSCNT CLRNC TO FL240. DURING OUR IDLE DSCNT WITH ENG ANTI-ICE ON; WE GOT A CABIN ALT WARNING HORN DSNDING THROUGH FL350. I NOTICED THE CABIN ALT WAS 11000 FT. WE ACCOMPLISHED THE QRH PROC FOR 'CABIN ALT WARNING HORN.' THE FO'S OXYGEN MASK MIKE WAS INTERMITTENT. IT HAD A SHORT IN THE CORD THAT COULD BE CORRECTED BY HOLDING THE CORD IN A CERTAIN POS. (IT DID TEST PROPERLY DURING THE PREFLT INSPECTION.) THIS MADE OUR COMS SOMEWHAT CHALLENGING. I REQUESTED A FURTHER DSCNT ALL THE WAY DOWN TO 10000 FT. WE HAD A DIFFICULT TIME CTLING THE CABIN ALT WITH THE CTLR IN MANUAL. WE NEVER RECEIVED ANY MASTER CAUTION OR 'AUTO FAIL' ANNUNCIATIONS. THE PAX CABIN MASKS DID NOT DROP. WE NEVER DECLARED AN EMER BECAUSE ATC APPROVED OUR DSCNT TO 10000 FT WITHOUT DELAY AND I FELT MY IMMEDIATE ATTN SHOULD BE FLYING THE ACFT AND TROUBLESHOOTING THE PROB. ONCE WE WERE BELOW 10000 FT; WE TRIED THE STANDBY PRESSURE CTLR AND IT WAS ABLE TO CTL THE CABIN MUCH BETTER THAN THE MANUAL CTLR. LNDG WAS UNEVENTFUL AND MAINT DISCREPANCIES WERE WRITTEN UP. WE SWAPPED ACFT AND CONTINUED OUR SCHEDULE.