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CBM (almost) universal power supply.

Like everyone, the power supplies of my good old commodores died a long time ago and the computers stored in the garage with the idea of making them work later...Life being life, that later turned into almost 20 years of storage until one of my 12 years old daughter asked me what in that box.

So i took a few transformer laying around in another junk box and made a terribly crude set of power supply capable of powering up the C64 and a 1541-II, turned the 1702 video cable into a S-VHS cable and hooked everything on the 50 inches tv of the living room... To my surprise, it worked even after being stored for so long in an unheated garage where it baked at +30'c in summer until being cold down to -40'c in february years after years.

Wha was even more surprising is the disk are still readable even after being stored like that too. But i know i have been pushing my luck quite a bit, And i want to restore then to good working oder. So i've decided to build a real power supply for them. And get back to electronic at the same time, since that had been stored in the garage of my mind before the C64 died...

I have started a projetc on Circuit Maker (A free CAD software that combine a lite version of Altium Designer and a collaborative hub) called "CBM Universal Power Supply", and did a first draft of what such power supply could look like.

The goals of the power supply is to:

  • Provide 5VDC/4A and 9VAC/3A for the computer.
  • Privide 5VDC/3A and 12VDC/3A for other peripherals.
  • Can be a single box with both supply combined, or two different module.
  • Should cost less than 100$ to build a prototype.
  • Look like a design that could have come from CBM (IE, not too fancy, minimum BOM to get things working correctly).
  • Be more reliable than what CBM used to pack as power supply.
  • Have fuse in it (there are 4 resetable fuses on the PCB).
  • Should not take fire (at least not on purpose).

Here's a look of the first draft of the PCB:


CBM Universal Power Supply

So feel free to participate in the design of such a little toy if you feel like it.

And no, i do not plan to sell this. But it's OSH, so if you want to do it, feel free.



Re: CBM (almost) universal power supply.

Sounds like one of Ray Carlsen's custom Commodore power supplies - the one that outputs both 5VDC and 9VAC for the Commodore and 5VDC and 12VDC for the other outboard accessories.

Back in California after having gone to Oregon,
Robert Bernardo
Fresno Commodore User Group

Yep, it is similar in a way,

Yep, it is similar in a way, the only difference being Ray using off the shelf components that he repack to make a power supply. But Ray's is giving me another idea, woudn't be hard to add a -12v and +9V to the 1541-II/1581 power supply, that would make it an Amiga and C16 power supply too...

Re: CBM (almost) universal power supply.

Here is a response from Ray Carlsen:

The designs appear to use a large power transformer with two secondary windings, then convert one of the outputs to DC with a switching circuit. But why re-invent the wheel? It doesn't make sense to me to design a new circuit to do what an off-the-shelf module can probably do better and cheaper. To make one or two of something takes a lot of effort... board fabrication, parts purchases, assembly, debugging and testing. Finally, I doubt anyone could build those circuits with only that board layout as a guide. You can't tell where all the board traces go since some are under the components. It appears to be an "artists conception" rather than an actual circuit design.


> The goals of the power supply is to: Provide 5VDC/4A and 9VAC/3A for
> the computer.

That transformer is going to be very large and heavy... and expensive. Why does the 9VAC need to supply that much current? The maximum Commodore used was 1 Amp and that was adequate even for after market hardware... unless there is something else out there I don't know about that needs more.

As far as the 5VDC 4 Amp part of it, that would be more than adequate for a C64, VIC20CR or Plus/4 but might be marginal for a C128 if accessories were used with it. The flat 128 OEM PS is rated at 4.3A and the computer alone draws 3 Amps!

> Provide 5VDC/3A and 12VDC/3A for other peripherals.

That would run several devices such as a 1581 or 1541-II, but here again, an off-the-shelf module can do it much cheaper, less than $20. Those modules will work overseas as well since they don't use a conventional transformer (auto-switch 120/230VAC input). An iron core transformer such as the "designer" suggests must have the appropriate input for the part of the world it's used in.

> Can be a single box with both supply combined, or two different
> module. Should cost less than 100$ to build a prototype.

I wonder where he got that figure. A large transformer will be expensive and cost a bundle to ship because they are very heavy. I couldn't find a source anywhere for a single output 3 Amp 9VAC tranny when I was thinking of making a replacement for the old VIC20 PS.

Multiple supplies in one box is a good idea (more cost effective than several smaller ones) but here again, the size of the case needed for all that hardware makes it very large, heavy and expensive to ship the completed version.


Let me see their finished version, tell me how much it actually cost to build, and then we'll talk. :-)


I don't want to start a war

I don't want to start a war with Ray! Geez!

He has all good points! And yes, the most expensive part in there is the transformer, which isn't there. Roughly the bill of material is 95$ for the two PCB and components, and 60$ for the two transformers (Hammond 266K18). So basically, if you make just one of the two power supply, you are under 100$.

The schematics and PCB layout is avalable on CircuitMaker (www.circuitmaker.com).

I'm not int he game of stealing Ray's business! I won't sell this and the only one i will make will be mine for my stuff. All i'm saying is if you want to do one, it's there, use it, modify it, sell it, wathever i don't care :)

The step-down converter and everything around it is capable of doing 5 amps at 5v or 12v, what is going to choke you is the transformer, it's a 27va and 5 amps is 25va, forget 5 amps at 12v with that transformer (Or switch to a Hammond 266P18, which is capable of doing 90VA)... The thumb-rule for transformer price is 1va = 1$ :)

It's easy to add a 120/240v switch to the AC input, yep it will not be auto-switching. The transformer is already designed for that.

Shipping cost is not in my design consideration at all. Yes, it will weight about 4lbs (each transformer is 1,58lbs).

An optimal design would be an all-switching transformerless power supply. But where is the fun in doing that?

If i was in the economical part of the hobby, Ray's the best option and he's doing the right thing. I'm having fun with this, that's all.

Link arms, don't make them!

Re: CBM (almost) universal power supply.

Eddy wrote:

> I don't want to start a war with Ray! Geez!

Heh, no war. Ray is just a very practical person who builds the best at the low cost and without sacrificing quality.

> I'm having fun with this, that's all.

Have fun! :)

Robert Bernardo
Fresno Commodore User Group

another opinion
Bill told me a few weeks ago
I gather that means that work
There are some information
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