New motherboard for the Commodore 1541 floppy drive


Probably it would now run every hardcore collector cold down the spine, but for me, the hobby is less about collecting. But rather that everything is in order and works.

In addition, it would be a nice tinkering, times to make the board new. Especially since I would finally get a correct circuit diagram. Because I would have to create this first of all new.

Because unfortunately none of the available schematics is really error-free. Neither the original plans from Commodore, nor those from various books (where many have simply drawn 1:1 and some have made additional mistakes).

The circuit diagram

As I said, an error-free circuit diagram was needed. In the meantime I have collected about 2 dozen variants of circuit diagrams. Everywhere I found small errors or deviations.

To create a new schematic was then also the most work. I took several boards of 1541 drives and compared them with the schematics piece by piece.

One board I have completely desoldered and measured the individual connections.

So I could, at least for one board type, determine a correct schematic. Whereby of course at the end always the question arose, what maybe the original circuit diagram correct, but the board an error …?

But since the drive boards work per se, this is for me the measure of things at this point.

With the creation of the plan I was also busy for several weeks. Again and again somewhere miscounted, or itself mistaken, led to the fact that I had to go back here and there again and again a few steps, in order to begin there again.

But in the end I had finally done it, and the schematic was ready:

I decided to use a hierarchical schematic, i.e. the top schematic represents the individual components, and behind each of these is a part of the schematic.

I did this in accordance with the service manual, which also represents individual parts of the circuit diagram according to function groups.

So, as I find, it is easier in troubleshooting. Because with an overall plan one is mostly rather distracted, than that one can analyze in peace.

The first PCB

The worst was behind me, at least in terms of workload. Now it was time to create a circuit board.

The dimensions and drillings were fixed, as well as the sockets and connections. I also took over the placements for the ICs exactly. The latter alone because of possible extensions, which were intended for the original board.

For the passive components I rather chose a “more or less like the original” placement. On the one hand because many components do not need so much space today, or because it was more favorable for the routing.

But basically it was already a pretty exact replica of the original.

The circuit board was created quite quickly. The routing cost me a good half day. Autorouter was out of the question. For me, this is rather something relaxing, similar to a good game of chess.

And this is how the board looked like in the layout program. Since I finished the board on 12/24, I thought it would be a nice gag to honor this on the board:

And then came the worst…

Good 3 weeks waiting for the ordered boards. There is almost nothing worse than this waiting. 🙂

But also this time went around (with the development of new boards) and finally the new board arrived. Quickly put a few more parts on it and there it finally is, the good piece:

(Note from 2021-04-03: I have replaced some pictures with newer versions which have a better quality)

Now I had a nice working schematic and a new board for the 1541. Now you could actually go there, and improve one or the other.

I don’t want to get too far ahead, but it wasn’t the last “new” mainboard for the Commodore VC1541 floppy drive…

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