What was found
THE FLIGHT DIVERTED TO DFW FOLLOWING THE LT BLEED TRIP WHEN THE ENGINE ANTI-ICE WAS SELECTED ON; ACCOMPANIED BY A LOUD BANG. AIRCRAFT DID NOT HOLD CABIN PRESSURIZATION OR AIRSPEED WITH ANTI-ICE ON. CORRECTIVE ACTION: MAINTENANCE PERFORMED LEAK CHECK OF SENSE LINES TO ENSURE PROPER OPERATION OF THE FAN AIR VALVE. NO LEAKS FOUND. THE #1 ENGINE PRSOV WAS FOUND TO BE INOPERATIVE AND WAS REPLACED. NO DUCT LEAKS WERE FOUND AND THE SINGLE PACK CONFIDENCE CHECK WAS GOOD. THE AIRCRAFT RETURNED TO SERVICE.