Thanks to Bob Roberts, the Robotron is now working pretty close to 100%.  I replaced the CMOS RAM chip on my spare CPU board, and now it is in good shape.  Here is a picture of the handiwork on the CPU board, and a picture of the high score screen after I played the first game with it working…

Now, the move joystick is a bit wonky, and as you can see from the picture of the screen, I think I need to get a cap kit.