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Commodore 64 PSU replacement

Posted: Fri Aug 18, 2017 11:55 am
by geraldholdsworth
Was moving my 'cave' around the other night and thought about the PSU for my C64, as I was moving it. It would be nice to be able to use a modern replacement for the supply, considering that the two 1571 (or are they 1541 mark II?) drives can run off a normal PC power supply. The only issue with the computer is the AC line it uses (IIRC, 5V+12V DC + 12V AC?). As it stands, they supply works fine...it's just a pain if it decides to die (and looks unfixable considering what Commodore did to those bricks).

Re: Commodore 64 PSU replacement

Posted: Fri Aug 18, 2017 12:11 pm
by geraldholdsworth
It's actually 5V DC + 9V AC. Apparently, the 9V AC is used to provide +5V and +12V DC inside the computer (so why the 5V DC from the PSU?), plus also feeds the Time Of Day clock (which is not used by anything). I'm not keen on modifying the computer, so it'll have to be a replacement PSU.

I was therefore thinking, what about buying a 240V AC - 9V AC adapter and taking a feed to regulate down to +5V DC?

Re: Commodore 64 PSU replacement

Posted: Fri Aug 18, 2017 1:19 pm
by 1024MAK
Funny you should post this today. Yesterday I spent more time than I care to admit to, looking for a matching PSU for a C128. I recently received a 1541 FDD and wanted to test it.

Now, I don't use the C128 that often. But do you think I could find the Commodore PSU for it...
I found one C64 PSU, two different A500 Amiga PSUs, two different A600 Amiga PSUs and a A1200 Amiga PSU.

Anyway, before I found a C128 PSU, I rediscovered my box with two C64C computers. So I tested the +5V from the C64 PSU that I had found. It measured 5.3V. So I hooked it up and soon had the C64C loading and saving to a new floppy disk (I had also been looking for my box of new 5.25" disks) :D

In the time when I took a break from my search, I searched the Internet to see what Commodore fans had to say about the various PSUs and what you can swap between the different computers. Well, not much opportunity for mixing and matching, what with different connectors and PSU outputs / computer power requirements :(

The easiest way to replace a C64 or C128 PSU, is to build a 9V mains transformer and a modern +5V SMPSU together in a new case.

I have only briefly looked at the schematics for the C64 and C128. But I believe the main logic is supplied from the +5V line and that the 9V AC feeds the audio circuit supplies, plus the +9V DC or +12V DC for the SID.

Mark

Re: Commodore 64 PSU replacement

Posted: Fri Aug 18, 2017 1:46 pm
by 1024MAK
Update to my earlier post, the 9V AC is rectified and smoothed and feeds a unregulated +9V rail (modulator supply and power to the cassette deck), a +5V rail (the colour video circuitry, the VIC chip), and the 9V goes to a voltage doubler circuit to feed a 7812 regulator to obtain a +12V supply. This also feeds the video circuitry including the VIC and the SID chips and the audio output transistor.

It looks like they tried to keep the video and audio circuitry supplies separate to reduce interference from the main digital circuitry.

Mark

Re: Commodore 64 PSU replacement

Posted: Fri Aug 18, 2017 10:23 pm
by geraldholdsworth
1024MAK wrote:The easiest way to replace a C64 or C128 PSU, is to build a 9V mains transformer and a modern +5V SMPSU together in a new case.

Think that'll be the answer - what I'll probably do is get a PC PSU to get the +5V and +12V lines for the C64, and also my two drives alongside the 9v transformer. Power all three from the one box. It looks like a modern PC PSU should handle the power requirements of all three units.

Cheers,

Gerald.

Re: Commodore 64 PSU replacement

Posted: Thu Sep 07, 2017 6:57 pm
by vanpeebles
I just got a C128 and sadly the coiled spring thingy (It looks like a large polo mint wrapped with copper wire) inside the PSU has busted loose. Whats the best way of fixing it? :?: :?:

Re: Commodore 64 PSU replacement

Posted: Thu Sep 07, 2017 11:28 pm
by 1024MAK
Post some photos...

Top and bottom of the PCB please.

Mark

Re: Commodore 64 PSU replacement

Posted: Fri Sep 08, 2017 6:49 am
by vanpeebles
Will do, I'll take some this weekend.