Replace That C64 Power Supply - Voltage Failure Will Kill Your C64

Do not use an original C64 power supply brick with your C64, or you may ruin you computer!

One of the joys of retro gaming is the opportunity to get things you never had “back in the day.” So it was with great enthusiasm that I laid hold of a vintage “breadbin” Commodore 64 (actually, it was a box with 3 of them). Fortunately, I had already heard about how the old ”Brick of Death” power supplies can fry your motherboard, and I dodged a bullet.

Do you know that Commodore 64 power supplies can fry your vintage C64? Never use the original power supply with your old Commodore 64. They are not well made, and being 35+ years old means it may fail soon, and fry your computer. If you have already used it, stop now, and replace it!

Table of Contents

Brick of Death: Don’t Use an Old C64 Power Supply!

For many of us playing old game systems, having original gear is an attractive part of the experience. When it comes to the Commodore’s wildly popular home computer though, an original power supply - cool-looking as they are - can be a real heartbreaker. In this case, a genuine original is not better - it’s considerably worse.

In a nutshell, the voltage regulator on the 5 volt DC output tends to fail in such a way that it lets a voltage spike go straight to your C64 motherboard, frying the precious chips.

RAM, or maybe your 6502 processor are dead when over-voltage hits them.

Commodore 64 Motherboard showing MOS 6502 processor, PLA chip, and RAM chips

And while you can test the power supply output (I show you how to test the voltage output below, just because it’s a good skill to have when working on gear), don’t rely on proper output now to stay that way later. The voltage regulator can fail unexpectedly at any time, and take out your delicate electronics.

Many people caution to NEVER use the old power supply, even for just a quick test. I tend to be conservative in my approach to taking care of my stuff, and I agree. Why risk a disaster for a momentary check? And if you have been using the original PSU so far without a problem, count yourself fortunate, and don’t use it any more.

Why is using an original Commodore 64 power brick so risky?

Many of these supplies were designed to operate using nearly all of their capability, so they worked very hard when they were being used. Add in the fact that heat tended to build up while in use, and that’s heavy wear on the power supply’s components. Additionally, they are now 35+ years older, so the scenario just isn’t good.

What Voltage Should the Power Supply Output?

Among power supplies for home computers and game consoles, the C64 PSU is an odd bird. It was designed to output two different voltages at the same time. It converts 110 AC wall current into the following two output voltages:

  • 5V DC (1.0 amp)
  • 9V AC (1.5 amp)

The C64 is designed (it’s not clear why this was decided) to need both of these. These two voltages come out through two sets of pins on the round 7-pin DIN connector that goes into the C64 power input.

C64 Power Supply Failure: What Goes Wrong

The following diagram is a simplified breakout of what the components inside the original power supply are doing in order to convert wall current into our two output voltages. The one that interests us is the pathway that outputs the 5 volts DC. It’s the voltage regulator on this that fails. At failure, it often stops keeping the output at the critical 5V, and lets higher amounts through, which then cause the nasty damage.

Diagram of key components in the Commodore 64 power supply, highlighting the voltage regulator failure point

Can the Original C64 Power Supply Be Repaired?

When I realized that my original power supply was a disaster waiting to happen, my first instinct was to see how I could repair it. I like solutions that save me money, and the unit is pretty cool looking... so I wanted to keep it.

Unfortunately, it turns out that the original “brick” units were not only low quality, but they are completely unrepairable, since they are potted. When they were manufactured, the case was completely filled with an epoxy that encased all of the components, and made them a solid, un-reparable lump.

Note that there was an early power supply version that looks different from the “brick” style pictured here, and it is repairable, but it is less common, and repairing one is outside of the scope of this article.

The C64 power brick is not repairable, due to its inside being filled with epoxy
The molded-style C64 PSU brick came in both black and off-white. Both are unrepairable due to their inside being filled with epoxy.

Why did they do this? Bill Herd, former engineer at Commodore shared a theory. (note that “CBM” in his comment is Commodore Business Machines) Essentially, it made them safer, and less prone to overheating and fire.

Finding a Replacement C64 Power Supply

The Commodore 64 was first released in 1982, and yet there is still a lively community of users, game makers (see my post on getting new “homebrew” C64 games), and hardware creators supporting it. You can do more with a C64 now, than you could back in the day.

Because this power supply issue is such a big deal, there are a number of people out there providing solutions. In my researching, I dug up several that have gotten good community reviews, and I will detail them here, starting out with the one I got for my own C64.

Electroware Commodore C64 PSU

Electroware (out of Poland) has created a very nicely done replacement C64 power supply option. It’s the one I went with for myself, and I am very happy with it. It contains two switched power supplies (one for each output), and built-in over-voltage protection. The build quality feels solid, and the cables on it are good and long.

The Electroware Commodore 64 replacement power supply unit

The final reason I like this PSU is that it has a power switch on it. The components inside are only in use when I switch it on, unlike a switchless one which draws power as long as it’s plugged in.

You can buy the Electroware PSU here >

(make sure you choose the US AC power cable)

Keelog C64 Power Supply

The power supplies created by Keelog have gotten good reviews as well. Like the Electroware units, they are also a modern, power switching design, with over-voltage protection. They do not however, have a power switch on them. Keelog does have offices in the US, though if that is of interest.

You can find the Keelog PSU here >

Ray Carlsen C64 Power Supplies

Ray Carlsen has been involved in the C64 community for some time, and is well known for high-quality builds, and great customer service. He has multiple options, with an “economy” version that is two spliced-together “wall wart” power supplies to provide the two different voltages. It’s not pretty, but it does the job. He also has a much more deluxe unit that is built like a tank in a steel enclosure.

The thing that makes Carlsen’s work stand out the most, is is custom builds. He will create power supplies that meet your exact needs - many times powering more than one device at the same time. This actually works out to be cheaper than buying two separate supplies from anyone else. Carlsen is also based in the US.

You can find Carlsen’s PSUs here >

Commodore4Ever C64 Power Supply

Another power supply option - with the standard switched supplies and over-voltage protection. It has a power switch, an LED display on the top showing amp usage, and an LED in the logo. It can also supply a much higher amperage on on the DC line (up to 4 amps), which can be useful if you want to run a modern peripheral off of the same PSU, like a Pi1541 (Raspberry Pi that emulates the 1541 disk drive). It also has a USB power port (good for that Rasp Pi). Note that the cases do appear to be 3D printed on these. They are also US-based.

You can find the Commodore4Ever PSU here >

Kevin Ottum’s Nu-Brick 64 Power Supply

In asking around far and wide, I had a number of people sing the praises of Kevin Ottum’s Nu-Brick PSU for the Commodore 64. I spoke with Kevin online, and he told me how he began with a solution called the Re-Brick, in which he repurposed the housing from the old PSUs and built brand new supplies inside them. From there, he has moved on to the ruggedly built Nu-Brick, which uses a metal housing in a color scheme that matches the C64 “breadbin” style, and a snazzy decal that looks like the C64 badges. The engineering is efficient and modern. Finicky users in our Dallas/Fort Worth Retro Computing group confirm that Kevin's work is top notch. He is also U.S.-based, in Iowa.

You can find the Nu-Brick here >

How to Test Voltage Output on a C64 Power Supply

As stated above, you really don’t want to connect an original C64 PSU to your precious C64, even if it is currently outputting the correct voltage. Failure can come unexpectedly, and I have seen people post about their woeful experiences. Don’t wreck your Commodore.

However, this is a good opportunity to learn how to test power supply output voltage. If you ever use a power supply (for any hardware) that you are at all unsure about, testing its output before using it is a safe way to proceed.

You will need a multimeter. It’s easy to find inexpensive ones everywhere these days. I tend to go for something a bit nicer, if I figure I will get use out of it. I picked up two different ones from Southwire - a manual range meter, and a snazzier auto-range one with True RMS (which helps with doing AC-related stuff). (Side note: I used my multimeter to troubleshoot and DIY repair the lock on the rear hatch of my vehicle, so it has helped me and saved me money!)

For something as simple as this, you can just borrow one (but if you tend to geek like I do, you may want your own).

Begin by plugging in your power supply, and making sure it is switched on if it has a switch like my replacement one does.

Make sure your red and black probe wires are plugged into the proper sockets on the meter, and turn it on. Switch the meter to the proper mode for measuring DC voltage (on an auto) or the proper range for measuring 20V DC (on a manual meter).

Commodore 64 Power Supply - DIN connector pinout for 9V AC and 5V DC output

1) Testing the DC Line

With the meter set for DC, we will ONLY be touching the contacts that output DC. We’ll do the AC ones separately.

Touching the correct pins on the round C64 DIN connector can be a bit fiddly. You will need one hand for each probe, and some way to hold the connector still (I used my knees). With the multimeter on the correct setting, touch the black (negative, or ground) probe to the proper pin on the connector as shown in the diagram above (in orange). Now bring the red probe over to touch one of the DC pins as shown above in blue. According to the Commodore 64 spec, either blue pin can carry the 5V DC.

You should see a reading a little over, or a little under 5. Mine came out at 5.27. Any reading around 6 or higher is a failed DC regulator.

2) Testing the AC Line

Now switch your meter to read AC voltage (auto meter) or whichever AC voltage is the closest to the expected 9V AC, while still being over it (manual meter). Touch the black probe to the orange ground pin shown in the diagram, and the red one to either of the pins shown in green in the diagram. According to the Commodore 64 spec, either green pin can carry the 9V AC.

You should see a reading a little over, or a little under 9. Mine came out at 8.53. The AC side of these PSUs does not tend to fail.

BONUS EXTRA: Hop over to the Intellivision 2 Power Supply page to see how to test a PSU that uses a barrel connector.

How to Open an Old Commodore 64 Power Supply

If you end up deciding that you want to open your old power supply, keep in mind that they are not repairable. Maybe you’re just curious. Maybe you have a clever idea for something to do with it. Whatever the reason, getting it open is actually pretty easy.

Supplies for Opening an Original C64 Power Brick

  • Normal-sized flat head screwdriver
  • Rubber or rawhide mallet

Flip the supply over, so that the bottom is facing up. Take a normal-sized (not small, for delicate work) flat head screwdriver and slip the blade in between the rubber bushing around the AC power cable, and the flat bottom piece that seals up the “brick.” Work it in, and slowly lever up the bottom piece a little, then move the blade around to another spot, and lever it up again until it begins to lift. Finish working it off gently until you have it fully disconnected.

Insert a flat head screwdriver at the power cord bushing, and carefully work your way around

Now that you have this done, you can use the mallet to strike the sides and top of the brick until you get the epoxy brick inside to separate from the plastic housing. Be firm with it, but don’t overdo it. When it loosens all of the way, you can remove it, and you’re good to go!