What was found
(CAN) SHORTLY AFTER T/O NR 2 PRV FAILED TO THE CLOSED POSITION. THE X BLEED WAS SELECTED TO OPEN AND BOTH PACKS WERE SUPPLIED BY NR 1 ENGINE BLEED. THE NR 1 PRECOOLER OUTLET TEMP THEN ROSE TO AN OVERHEAT CONDITION AND CLOSED THE NR 1 BLEED RESULTING IN THE LOSS OF BOTH PACKS.AFTER THE TEMP COOLED DOWN NR 1 BLEED WAS RESET AND SELECTED ON WITH NO OPERATIONAL IMPACT. MAINTENANCE REPLACED THE NR 2 PRV AND INSPECTED THE NR 1 BLEED SYSTR. WITH NO FINDINGS. BOTH ENG'S WERE RUN AND ALL BLEED SYS'S OPERATED NORMALY