What was found
AT FL 350, PRESS MODE SELECTOR IN AUTO, THE ALTITUDE 'CABIN' WARNING HORN SOUNDED. EMERGENCY DECLARED. EMERGENCY DESCENT ACCOMPLISHED. PASSENGER MASK DID NOT DROP. CABIN ALT INCREASED TO APPROX 12,500 FT, MAN PRESS OK. REPLACED CABIN PRESSURIZATION CONTROLLER, OPS CK OK PER M/M.