As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXPERIENCED A NR 2 PACK FAULT ON CLIMBOUT WITH THE NR 1 PACK ALREADY ON MEL AND LOCKED OUT. THE AIRCRAFT RETURNED TO DEPARTURE WITHOUT INCIDENT AND NO LOSS OF CABIN PRESSURE. TECH ACCOMPLISHED TROUBLESHOOTING IAW TSM 21-51-00-810-803-A FOR THE NR 1 PACK. REGULATOR WAS REPLACED DURING THE NEXT OVERNIGHT MAINTENANCE OPPORTUNITY. NO FURTHER FAULTS RECORDED DURING SUBSEQUENT FLIGHTS.