As well as looking at the CPT4200, I have recently acquired some CPT8500 series PCBs. I have enough PCBs for 2 85XX machines, but no backplanes or any other parts.
These are some of them:
That’s a memory card (256K) and a processor card (8080 based).
I have a display controller:
And a disk interface card.
None of this is much use without schematics, and I have been very lucky to have been corresponding with a former engineer at CPT who has been very helpful and supplied a lot of information about the cards and also schematics of the 8000 model, which, although not this model, has the same circuitry.
A backplane is needed in order to do anything with these cards, I think a Gotek can be used to emulate a disk drive and I should hopefully be able to create some form of video display. The keyboard is a CPT designed one, and I have enough information to build one in hardware or, more likely, a Pico based version.
So, first a backplane:
I also need a debug facility, so have made a card that plugs into the backplane and has a Pico on it. That sits on the bus and so should be able to trace the bus traffic and maybe even do things like test the memory card etc, if the processor card is removed.
All of this came together this morning with an ATX PSU:
I powered up a processor card and after about 3s there was a bang and some sparks. A tantalum capacitor shorted.
After replacing the capacitors, I powered up again and a yellow led lit up, then a green. I think this is the processor starting up.
I then replaced the tantalums on a memory card and powered that up too.
I have a reset switch on the backplane, that’s what I am pressing in the video above. I wasn’t 100% sure it was a reset signal as it was called CLEAR, but it looks like it was.
I had a look at my other processor card and it looks like this in one corner:
It looks like someone else had my tantalum issue…