Building My Replacement Commodore 64 Power Supply

With how frequently it is discussed in the retro Commodore community, I’m confidient that you have already heard about how the original “power bricks” for the C64 can fail and take the computer along with them. Here, let’s have a look at why this is the case…

Yup, that’s a giant soup of 30+ year old glop that many refer to as epoxy, but I am starting wonder if it’s actually toxic waste that the company decided to get rid of on the sly… Seriously, the stuff inside this old brick still sticky depsite the container having a few cracks around the wire holes for air flow. It stinks, it’s gross, but most importantly it traps heat and heat significantly reduces the functional life of capacitors and voltage regulators. Unfortunately, in this type of circuit, when the voltage regulator goes bad it tends to send waaaay too much voltage through it – components rated for 5 volts will usually burn out when given more than 6 volts, but in this case they can receive up to 9 volts. On the Commodore 64, it’s usually the fuse, RAM, and other logic chips that die due to power supply failure.

Now I am sure you may be wondering, “Rob, why not just buy a new power supply from Ebay or the like?”, because there seem to be quite a few to choose from at present. Well, dear reader, they’re expensive from the get go and are made even more so by the low value of the Canadian dollar, shipping charges, duty charges, and taxes. An item listed for $50 USD can easily cost me more than $100 CAD by the time its in my hands. Don’t get me started when it comes to buying anything in British Pounds! Unfortunately, no one in Canada is making power supplies for the Commodore 64 to my knowledge, so I’ll just make my own that is good enough and inexpensive (I only spent $1 on it!).

Moving on… let’s have a look the original “full wave rectifier” style power supply that was included with all Commodore 64s.

A respectable design, even by today’s standards, but it has some shortcomings. The biggest (and heaviest!) issue with this design is that it relies on a large transformer to step house electricity down to a level that can be used by electronics. Considering that we routinely charge our mobile phones using small, light bricks, you might be wondering why Commodore would ever use this massive transformer. The long story short is that it’s a very good transformer, with components that can handle much larger current than what was really needed to do the job, and that was a common practice in the 70s and 80s. Seriously, the copper windings inside this thing look like they were made of 16 guage wire! That’s excellent for allowing lots of electrons to flow and to induce a strong current on the equally hefty secondary windings (how a transformer works), but it’s not really needed in this case. And where there is a lot of current flow, there is a lot heat generated! Sadly in this case, that heat got trapped in an big o’l box of chemically putrid goop…

The second issue is the “full wave rectifier” circuit design itself – it’s simple and inexpensive, but it’s not very fault tolerant – if that voltage regulator breaks down, as I wrote earlier, up to the entire input voltage will be applied to the device, which can be disastrous. Also to be noted here, Commodore decided to save 1/10th of a cent by using a “full wave rectifier” design, rather than a “bridge rectifier”, using only two diodes instead of four – truly odd, because it requires a beefier transformer, which you’d think would be more expensive than two extra diodes. Anyway, it’s not the most energy efficient and fault tolerant design.

It’s for these two reasons that nowadays you will usually find power adaptors that use the “switching” method of stepping house electricity down to levels that are safe for electronics. Switching is a simple concept – it literally switches the power on and off really fast, such that it reduces the overall voltage that leaves the output. This switching happens many times per second and the components that take care of it are reliable and do not consume much power to get the job done. While there are some potentially dangerous side effects of this method (holding the output of a USB charger and touching your stove could produce a current so strong it would stop your heart, due to the “potential difference” if the stove isn’t properly grounded), none of them are likely to occur. For the life our electronics, an important feature of switching power supplies is that when they fail they just “stop working” without breaking the device they are attached to. Yay!

Hopefully with this background knowledge in hand, you’ll understand why I chose to use pre-made “wall wart” power supplies to build the new power supply for my Commodore 64!

From left to right those are…
Linksys 9V AC / 1A – For the C64
2Wire 5.2V DC / 2.2A – Also for the C64
Radio Shack 9V DC – For my Arduino!

Yup, because I decided to use the very nice aluminum case from my old PC power supply, I had enough room to include a power supply for my Arduino as well. This will be handy for larger projects that will draw more current than what the USB port on the computer provides (500mA), as I can plug it into a secondary power adaptor to power the components on the breadboard separately from the Arduino. Also, I can run the Arduino without using a battery or the power from my desktop PC. I digress!

As we frequently do in life, I unfortunately learned the hard way that what I was about to do wouldn’t work. That’s life man, that’s life!

As it happened, the the 5v adaptor I picked up from a thift store for $1 was insufficient for powering the Commodore 64. While it was rated at 2.2 amps and my (cheap and limited) multi-meter indicated that it delivered 5.19 volts (which I initially brought down to 5.02v using a 10K & 330 ohm voltage divider), my C64 failed to turn on when it was in use. Here are some pictures of my progress to this point. Note that I removed the Radio Shack wall wart from its case so I could use the 9v AC off its transformer for the C64.

Incidentally, the 9v DC Radio Shack supply powered the 12v DC power supply fan just fine, even with its 4 awesome LEDs! Heh, that was pretty ahead of it’s time when I bought the power supply in 2007 or so. πŸ™‚

This ATX power supply served me well for more than 10 years before giving up the ghost!

Thinking about how to put them in there…


The guts of the 5.2v wall wart, which I took apart to see what was loose inside. Turned out to be an inconsequential chip of the plastic shell. Also, a nice chunk of steel plate from some other thing I took apart at some point.


The guts of the 9v DC Radio Shack wall wart. The cheap buggers used a 9.6v transformer and a very simple bridge rectifier circuit to make the 9v DC. If I had an ocilicsope I’d show you how noisy that DC current wave form must be, but I don’t have a scope. It should look like ____ but I bet it has lots of ripple, like so ~~~~~. That said, it’s good enough for a fan and my Arduino projects!


Note the plastic shim under the board that prevents it from shorting out on the mounting plate! It’s a piece of the lid of an old laundry bin.

The Arduino works!


The resistors that make up the voltage divider for 5.02v DC, before I applied the heat shrink wrap, and the 9.6v AC (orange wires) all wired up to the C64 connector.


So at this point the computer didn’t turn on, not even the power light. Initially I thought that the problem might have been the 9v power supply, as the Radio Shack one was 9.6v at 500mA unloaded, where as the Linksys one was 11.89v at 1A unloaded. Just to make sure I hadn’t blown up the C64 completely, I pulled out the wall warts I used to power my VIC20 (of which the Linksys wall wart was one)…

And my C64 was indeed still functional! Pardon the picture of the VIC20, what you’re supposed to be looking at is the “wall wart” power supply. πŸ™‚

So I disconnected the orange wires from the Radio Shack transformer and installed the Linksys wall wart. I left the Linksys one inside its case, because I didn’t have a need to open it.

Nope, this didn’t work either!

Well, that left the 2Wire 5v wall wart as the problem. Too bad really, because it was rated for 2.2 amps, which should be enough to drive the Commodore 64 and the Ultimate 1541 II+ Cartridge (which itself is a little computer), where as the little 1.8 amp wall wart that I used with the VIC20 probably will not have enough juice for the job. I guess I will find out next month when my Ultimate II+ arrives!

I wanted to be able to use the Commodore 64, so I decided to put the 1.8A / 5v wall wart from my right-busted Blackberry Playbook tablet inside there for the time being. Yes, that means after all that effort I am… using exactly the same wall warts that I used for the VIC20 last year! lol… Such is life folks! πŸ™‚ Check it out in all its majesty!

Originally this ATX power supply had two fans, one pushing air in and the other blowing air out. It’s plenty efficient in this case with the one fan blowing into the case and air escaping out the vents.

If the the Playbook wall wart isn’t able to power the system properly, I’ll order a Mean Well RS-15-5 5V/3A power supply (from Digikey, as they appear to have the lowest price, for both the item and shipping costs, that I can find). The Mean Well is designed for industrial use and will be quick to swap into the power supply case. In the mean time, the girls and I will continue to enjoy puttering with BASIC!

Go Baylea, programmer extraordinaire!

So proud!


Disclaimer:
I am a person who learned about electronics in high school and college in the 1990s. I am not an expert in the field and this post is for your entertainment and general information only; it is not a definitive guide on how-to build something. Importantly, I was taught how to properly handle high voltage electrical systems and how to use a soldering iron, while you may not have been!

Please be careful and do your research before working with electricity, chemicals, and high temperatures. Even better, find real life people who can bestow their knowledge and experiences upon you in an environment where you’re able to ask questions and listen to answers until you fully understand! Ask around at school or work or check your local social media / forums / papers for hobby groups such as makerspaces or computer/electronics clubs.

Note: I’m not affiliated with any links provided in this article, they just exist for your reference.