What was found
(CAN) AFTER T/O, UNABLE TO PRESSURIZE ACFT, RETURN, SUBSEQUENT OVERWEIGHT LANDING. RESOLUTION POST FLIGHT REPORT SHOWED, NO CPC 1 ANALOG SIGNAL. ON GROUND UNABLE TO FAULT SYS 1, 2 OR MANUAL CONTROL. REPLACED CPC NR 1 IAW AMM 21-31-34 PB401 AND OPS TEST OF THE PRESSURE CONTROL AND MONITORING CHECKED OK FOR SERV.