Let me start with the fact that I know next to nothing about NSM's, but I've managed to fix all <20 I've worked on.
I have a Prestige II with an ES2 system that acts odd. Lets say to make a selection 123. Press 1 - OK, press 2 - OK, press 3 and the 3 goes into the 2nd digit place so it's reading 13. Additional pressed buttons will show up in the second digit place with 1 staying as the first digit. What makes it more odd is that yesterday something happened and it worked correctly until it was turned off and on again, then it went back to making the strange selections. I have another credit/selection computer and that one works correctly all the time. Tried powering it up with the cabinet switch open and closed with no difference.
Tony