My Commodore 64 PSU project.


Ive been asked to explain how I made my first C64 “saver” back in the 1990’s I sold the thing many years ago, so I have no pictures of the original thing, so I’m going to explain how to make one today, with the tools and equipment that are available now.

I did not want a solution that is more expensive than a full computer setup with games and accessories. After all, its just a PSU. Second, I want to avoid any legal or insurance problems by making a homemade PSU that connects directly to the mains. The rules here are strict, its not enough to use components that are certified, the assembly itself must also be certified. That would cost more than a house. So how do we work around this? Simple. We use already made and certified off the shelf solutions! Background: A well known and well documented fact about the C64 PSU is that it has a tendency to fail in a bad way. Sometimes the 5v output regulator fails intermittently and delivers a too high voltage to the C64. The RAM and TTL circuitry usually wont tolerate more than 5.5v before it craps out. Especially the RAM is vulnerable to small fluctuations to the 5v rail.  Part of the problem is that the powersupply seem to work great for a while and when cold, but after a while it suddenly fails. My solution is designed to attack this specific 5v problem without destroying the original PSU. I also made a solution for machines with no PSU at all. Now, what is so special with this C64 psu anyway? Well, its not THAT special. It uses a standard 7pin DIN plug, where only 4 pins are used. Next it has 2 different outputs. One is 5VDC, and one is 9VAC. Not at all complicated. These are the components I use to make my C64 PSU solutions.


This is all you need for a full replacement of the original PSU. You can easily make small adjustments to change the setup. If you plan to use the 9vac for the original PSU, you can swap out the red plug with a 7 pin DIN female connector to “steal” the 9vac from the original PSU. A 9vac PSU are not the easiest to get hold of these days, so using the original PSU for this is a great solution. Its perfectly safe too, because the 9vac from the original PSU are pure unregulated power straight from the transformer. It eighter dont work or it works as it should. Other things you can save money on is to not use the LCD voltmeter display, its only there to keep an eye on the 5v and is not needed. You can also skip the PCB shown at the lower left side. The reason why I put that in, is to be able to use any power supply I might have handy, and no matter what I connect, his puppy regulates it down to a clean 5vdc. I can now use anything from 9vdc to 30vdc as long as the plus (+) is in the center pin. Like a good quality psu from a laptop, which is usually anything from 12vdc to 20vdc, well inside the capabilities of the converter. The PCB also has over voltage and polarity protection. If you skip the pcb, then I would recommend putting a fuse and a diode on the dc input.

The red connector I use to connect the external 9vac from a wall adaptor. The small black is for the dc input. If you dont use the pcb, you must use a 5vdc adaptor in that plug. I found a D-link psu for an old router. Its perfect for this project. Maybe you can find one at home or at a fleemarket. The original psu are rated 1A for the 9vac, and 1.5A for the 5vdc. For the 5vdc, I would recommend 2A (2000mA) or more.

Make sure you dont use too long cable from the box and into the C64, because you can easily get a voltage drop big enough to make the machine behave weird. You can compensate by using thicker cables if you need longer cable, or by measuring the voltage inside the machine, and compensate for the loss by lightly increasing the voltage on the pcb. (if you use one)

Its worth to mention that using the 9vac from the original psu is better, because then there is no chance of you connecting 9vac to the 5vdc plug or vive-versa. The reason why I went with red plug for the 9vac is to avoid plugging it in the wrong hole. You can of course use different connectors for the ac and dc inputs to avoid problems. Using a Micro USB for the 5vdc would be perfect, since those always provide 5v.

Your end result might look something like this.



This version have a 7pin DIN input at the top of the picture to “steal” the perfectly safe 9vac from the original Commodore PSU. I usually make a version depending on which machine it’s supposed to be used on. I have even used the plug and wire from a dead Amiga PSU to make a PSU for the C128. They are extremely hard to get hold of, so never throw away a dead PSU from any Commodore product. Someone definitely have use for it! 😀