On Fri, Feb 21, 2014 at 10:08 PM, Charles <charlesmorris800 at centurytel.net> wrote: And the I/O connector points towards "F" - that's characteristic of the PDP-8/a chassis. PDP-11s have a backplane connector where the PDP-8/a has a gap to route the cables. That is a mystery board. If you see a pattern off of it of sets of 8 lines (data bus, address bus) in the same place as a Z-80, then it's possible, but I think it's more likely that it's a peripheral chip than another CPU. I'd start with guessing it's a serial chip and trying some of the common ones Those look like smaller versions of connectors I've seen on a Qbus Pertec video card. Those _were_ coaxial, with tiny center conductors. What are the chips that are directly attached to those I/O pins? You might learn something if you can decipher the physical layer. -ethan