What was found
PDIS 298 21-30 2907 26FEB19 LAX FACT U LOGPAGES:3042464 ON CLIMBOUT RECEIVED " CABIN ALTITUDE " WARNING LEVELED OFF ALERT WENT AWAY , AIRCRAFT PRESSURIZED TO BELOW SEA LEVEL AND BEYOND MAX DIFFERENTIAL PRESSURE . AIR TURN BACK FACT 26FEB19 17:04 LAX U PER CREW DEBRIEF CABIN ALT ALERT OCCUR IN SYSTEM 1 SWAP TO SYSTEM 2 ALERT WENT AWAY AND WENT MANUAL. PERFORMED BITE ON BOTH CABIN PRESSURE CONTROLLERS IAW FIM 21-31/803 NO FAULTS. USING CABIN PRESSURE SELECTED MANUALLY CYCLED OUTFLOW VALVE WITH NO BINDING. VISUALLY WATCH OUTFLOW VALVE OPEN/CLOSE WITH NO ISSUE. REMOVED AND REPLACED NO.1 CABIN PRESSURE CONTROLLER REF AMM 21- 31-02-04. PERFORMED BITE CHECK REF AMM 21-31-00-5. MANUALLY PRESSURIZED REF AMM 05-51-24-2. OPS CHECK GOOD. NO FAULTS NOTED. AIRCRAFT OK FOR SERVICE.