As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR TURN BACK AFTER T/O "CABIN PRESS REG 2 OFF" BOTH REGS INOP. RESULTING IN AN ATB FOUND FWD PRESSURE REGULATING VALVE MONITORING CIRCUIT READING APPROXIMATELY 145K OHMS AND ALL OTHER MONITOR CIRCUITS FOR AFT VALVE READING 25K OHMS. R/R FWD PRESSURE REGULATING VALVE REF AMM 21-31-12/0401. ALL SYSTEM TESTS PASSED, REF AMM 21-31-00/501. THIS CLEARS THE DEFERRAL.