The linked MS Word document provides instructions for replacing the main board.
Scope: replace the main PCB with p/n 4815126 – “SERVICE PCA, CHASSIS, PROCESSOR / COMMUNICATIONS - WITH SOFTWARE”. This board is shipped preprogrammed with software and is a drop-in replacement for use with the 6270A. The calibration data of the Pressure Measurement Modules is not affected by board replacement as the calibration data for the PMMs is stored locally with each module.