Commodore CP/M module disassembled and rebuilt

Much has already been written about the history of this module. Therefore, I will spare myself repeating this partly quite sad story here.

Rather, my contribution is about rebuilding this module.

Since not many modules have been sold at that time, it has also it is also a small rarity. Or just to try it out. In my opinion it is worthwhile in any case to rebuild this cartridge.


I have the module in the 80s itself can find used somewhere. At that time there was unfortunately no Internet and above all no possibilities somehow to convert disks or to write over a PC (which one did not have also at that time) on a disk.

So I had the module and the CP/M system disk, but otherwise no software. I knew CP/M at that time already from my Kaypro and from the Apple II.

Only because this cartridge only works with the Commodore 1541 floppy drive, I could not use the floppies of the Kaypro or Apple II on the Commodore. So the module disappeared sometime in the cellar.

So this cartridge came back as a quasi basement find, even though it was my own basement this time.

The module even still worked. And for the first time I could run various programs like Turbo Pascal or Zork on it.

And since it is somehow a part of Commodore history, it would be a good opportunity to recreate this module.

Now there are several schematics for this module on the internet, but none of them seems to have been checked for function or correctness. Also there are always small deviations to be found, which moved me to draw my own schematic.

The wiring diagram

The board is actually quite tidy and the components are kept within limits. Unfortunately, not a single IC is socketed.

Now you could try to somehow unravel the individual traces by measuring and tracing. The problem are the traces that go under the ICs.

So I did the only really sensible thing, I freed the whole board from its components. I have desoldered everything. Since I have the necessary equipment in the form of a professional soldering / desoldering station JBC DMSE-2QA, this was also a piece of cake.

And above all, completely without damage to the soldering eyes or traces.

Afterwards I scanned the two boards with a flatbed scanner.

This way I had a clean front and back side of the board afterwards.

PCB – Commodore CP/M Cartridge

Front


PCB – Commodore CP/M Cartridge

Back

Now I “only” had to trace all the traces. That was actually also the most work, whereby here also special attention must be paid.

There are always small connections directly between two soldering eyes, which are not always directly noticeable.

So the first board was created, from which I could have directly output Gerber files. However, I still would not have had the circuit diagram with it.

There are tools that try to design a schematic from it, but experience has shown that doing so requires more rework than drawing a new schematic

Commodore CP/M Cartridge

“First PCB”

So now I could go through every single connection and trace it in a layout program.

This is how the following layout was created.

Commodore CP/M Cartridge

Schematic

By the way, all files, including this schematic as PDF, are on GitHub. The link can be found at the end of this post.

And from this a new circuit board was made. I have kept the same dimensions as the original. Also the component positions are the same, even if some components are adapted by the size somewhat to the current components.

And this is how the new board looked like in the computer model.

Commodore CP/M Cartridge

New PCB

As a 3D model, it almost looks like the original.

Commodore CP/M Cartridge

3D Model

And this is how the assembled board looks like in the end:

Finished replica

Download

If you want to rebuild the cartridge, you can find all necessary files and information on my GitHub account: https://github.com/DL2DW/Commodore_CPM_Cartridge

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