The computer appears to be working electronically now. There are a few things that seem a bit wonky. The Reset/Hold/Operate switch may be a bit dirty, since it was not working reliably at first, but using it seems to be clearing it. Also, I can't get the meter to null pots when the voltage is negative, so there is something not right there that I'll have to fix.

But, it works and it computes. The circle to the left is what you get for y''=-y, where I'm plotting y in one axis and y' in the other. Since the answer to this equation is a sinusoid, you expect it to plot a circle, which it does. Interestingly, it will draw over that same circle over and over again with no apparent drift. After all these years it is rock solid. The plotter did start to have problems in one axis after a while, so I'll have to work on it.  But, the computer really does work.

It is all together other than the case, which I'm painting. I should get it installed this week. I'll look at that pot bus issue and tear back into the printer again to see why the X axis is binding up.