The infamous killer C64 PSU

Snappy title eh?
Important though!

Warning about C64 power supplies

This is the most important piece of advice for anyone with (or looking to get) a C64.
DO NOT USE THE ORIGINAL PSU - I Cannot stress this enough.
If you are currently running your C64 on its original PSU, unplug it immediately.

C64 power supplies can be found all over the place and generally, they either work or they don't. Those that do work, appear perfectly fine. All voltages read correctly and the C64 runs perfectly.

The PSU supplies two voltages, 9v AC and 5v DC. The 5v DC is provided by a regulator inside the PSU case (fed from the 9v AC transformer). It is this 5v regulator that causes all the damage.

Often, when this regulator fails, it lets a much higher voltage through to the C64. This in turn, usually causes damage to chips inside the machine. In the 80s and 90s this wasn't a huge issue. There were spare parts galore (many of them still being produced). In 2024 however, genuine C64 chips are decreasing in supply to the point where people are developing replacement chips using modern methods. As good as some of these are though, it's still much better to retain the original chips and one of the ways to enable that is to never use the original C64 PSU.

Also, there is no warning of the failure. It works and then pop, suddenly it doesn't. No funny warning noises, odd smells or feelings in your bones.

OK, now you're looking at your freshly unplugged C64 wondering how you're ever going to complete Midnight Resistance.

Fear not, I have several solutions to this dilemma!

C64 PSU saver

This snazzy little device sits in between your PSU and C64. There are several designs available to make one or you can buy pre-made units from various places. Here is one example. This is one of the first links I found when searching for "C64 Power saver"

Aftermarket PSU / DIY PSU

If you do a search for "C64 PSU", you'll find plenty of results for aftermarket power supplies. I don't have any experience with any of these so cannot recommend any specifically but it shouldn't take long to work out which one prefer. I may buy myself one eventually so will expand on this section if I do.

There is also the option, if you're inclined and possess the necessary skill, to build your own. All the information you need can be found easily online (and will be added here eventually). All you need are the parts and tools and you're golden.

One important note here is that the DIY route really is only for people experienced with electronics (specifically with power circuits). While I often encourage "having a go" there is too much risk involved both to the C64 but also yourself that if you don't feel you could do it without a step by step guide, then leave it for now. You can always revisit the idea later when you've gained more experience.

This is what I intend to do next.

Original PSU mod

Again, this isn't a great option for people inexperienced with power circuits but the last option is to modify the original power supply and add an external 5v supply.

This is the ghetto version you use in a pinch to get yourself up and running.... like I did 6 months ago.

As explained above, the PSU outputs 9v AC and 5v DC. The AC part of the PSU is perfectly (as far as we know) reliable and is safe to use. What I did was cut a bit of cable cover off a section between the PSU and C64 plug so that I could see the wires. Then I worked out which cables were the 5v wires and snipped them. I used a multimeter and web searches to determine which was which.

I then soldered a barrel connector to the two exposed wires (ensuring the correct polarity) and taped everything up as nicely as possible.

Now I can plug any 5v DC power supply in that provides enough output and the original PSU provides the 9v AC.

I will add photos shortly.

Conclusion

I'm a firm believer of forming an opinion from multiple sources however in this case, I hope you'll believe what I've written about the dangers of C64 power supplies and take action. If you wish to validate this article against other sources, please be my guest. I'm not an expert by any stretch of the imagination.