What was found
(EMERGENCY DECLARED) CAB PR SYS 1 FAULT IN FLIGHT, EXCESSIVE CABIN ALT MASTER WARNS SHORTLY AFTER, OUTFLOW VALVE SHOWED 1/4 OPEN ON SYSTEM PAGE. CABIN ALTTUDE EXCEEDED 25000, O2 MASK DROPPED. SYSTEM WAS IN AUTO ECAMS COMPLIED WITH. / CPC1 (11HL) WAS NOT RESPONDING. REMOVED AND REPLACED CPC1 (11HL) IAW AMM 21-31-34-000-001-A AND 21-31-34-400-001-A. PERFORMED OPS TEST OF PRESSURE CONTROL AND MONITORING IAW AMM 21-31-00-710-002-A. PERFORMED OPS TEST OF MANUAL MODE SELECTION AND MANUAL MODE PRESSURE CONTROL IAW AMM 21-31-00-710-003-A. PRESSURIZED CABIN IAW AMM 05-53-00-780-002-A01. ALL SYSTEMS OPERATING NORMALLY, OPS CHECK GOOD.