What was found
AT 23,000 FEET, CABIN PRESS ALTITUDE WAS CLIMBING MORE THAN 1,500 FEET PER MINUTE. ENG & WING ANTI-ICE WERE ON. CLOSED OUTFLOW VLV, BUT COULDN`T CONTROL CABIN PRESS. EMER DECLARED. EMER DESCENT TO 10,000 FEET. FLIGHT RETURNED WITHOUT FURTHER INCIDENT. PERFORMED PRESS CONTROLLER CHECKS IAW 21-32-00, ACFT DECAY CHECKS IAW 21-00-00, OUTFLOW VLV CHECKS IAW 21-32-05, WIRING CHECKS IAW 21-31-00, & PACK CONFIDENCE CHECKS IAW 21-00-00, NO FAULTS FOUND. THE ACFT WAS GNDED.