I seem to remember a small board with a battery backup. If it's what I think you should replace the battery to retain the memory. Then you can switch out the main board.

depending upon the vintage, you may have to do a re-init. or possibly an init. a re-init is usually no problem. If you init you lose all the parameters that were changed by the Adjuster at the time of install. I suggest you go through and copy down the drive changeable functions.Usually these changes were recorded on Parameter sheets and left in the controller. If you remove the ee prom chip from the old CPU to the new CPU you retain all the old parameter changes such as floor table, timers and such. ON older Analog controllers I think U-17 was the ee-prom chip. I can,t remember what it is on the newer digital controllers. The small baby board attached to the CPU is the program for the job and is not affected, only the Drive and the above mentioned e-square proms are affected by changing the CPU. Good Luck.