Build your own Commodore 64 power supply

Hobbyists have been building their own replacement C-64 power supplies for decades. I first talked to someone about it in the mid 1990s, when I was still in college. But no one, to my knowledge, has ever given a step by step build process for a DIY power supply. So I will. Here’s how to build your own Commodore 64 power supply.

All you need to build a DIY C-64 power supply are the two cables you can make or salvage from an original power supply, a 9V transformer, a 5V switching power supply module, a case to put it in, and possibly some bits of wire and wire nuts. The only tools you need are a screwdriver and a multimeter.

Build your own Commodore 64 power supply vs buying

cheap enclosures for electronics projects
You can build your own Commodore 64 power supply from off the shelf parts, put it in a tin box like I did, and enjoy clean, reliable power for years to come without a great deal of effort.

I will recommend specific parts for this, but mainly because it makes the build process easier. You can substitute parts if you wish in order to save money. My choice of components may cost you $10 more, so it’s up to you to decide if the time you save is worth $10.

Some of the parts I recommend are more rugged than the C-64 needs. I couldn’t find a better match that was as easy to use. I’d rather have one that’s a bit over-spec and easy to build, so that’s why I designed this the way I did.

What about tools? All you really need are a drill, a screwdriver, and a multimeter. If you don’t have a multimeter, you can get one very cheaply, or even for free, from Harbor Freight with a coupon.

Several people offer quality replacement power supplies. You can build one for $35 or buy one for $50. The question is whether you want to pay someone to assemble and ship you a box ready to go, or build one yourself to save around $25.

Unless you have one of the scarce heavy-duty models, don’t use a vintage Commodore power supply.

Switching vs linear power supplies for the C-64

I’ve seen some debate about using switching power supplies vs using traditional linear power supplies. Commodore used switching modules in its heavy duty power supplies, so I see no reason to not use them today. Switching power supplies are more efficient, so they run cooler and last longer. And today they’re cheap and plentiful. They weren’t so cheap and plentiful in 1982.

I don’t view it as a compromise to build a power supply using modern parts. Our goals are different from Commodore’s. Commodore’s goal was to design machines that would last 3-5 years and hit a very aggressive price point. Our goal is to keep a machine designed to last 5 years working now that it’s several decades old.

Parts I recommend

First of all, I recommend a 5V switching power supply module of at least 2 amps, or better yet, 2.5 amps. The Mean Well RS-15-5 is a good choice. It’s 3 amps, but has screw terminals for easy assembly and it’s reasonably priced. It will provide plenty of clean, stable power on the 5V rail while running cool.

Next, you need a 9V AC transformer of at least 1 amp. Expect this to cost more than the 5V switching power supply, due to economies of scale.

Finding pinouts

The Mean Well RS-15-5 has all of its terminals labeled, so that part’s easy. If you buy a different switching power supply, you’ll need to refer to its datasheet to figure out which pins are which.

The transformer can be trickier. The 9V transformer I got had three wires on each side, which is confusing for something that’s supposed to step 115 volts down to 9 volts. It turned out the thicker wires go to the mains, which is conventional, and that one of the wires is for 220 volts and the other for 115. On the other side, one combination of wires gives 9 volts AC and the other gives 6 volts.

If your transformer comes with a datasheet, that will tell you which wires to hook up to step your country’s household current down to 9 volts. You can ignore the center wire. If you don’t have a datasheet, you’ll need to temporarily connect the thicker wires to your power cord, leave ground unconnected, and then measure the output from the thin wires until you find a combination that gives you 9 volts. If all of the combinations of wires read high or low, you connected the wrong combination of wires to your outlet. Try a different combination, then label what works.

Salvaging cables from Commodore supplies

You can save a lot of time and effort and money by salvaging cables from an old C-64 power supply. Just pry off the bottom, then snip each of the wires from the power and computer cables inside. If you don’t have an old Commodore power supply to plunder wires from, you can buy 4-conductor cable and a DIN 45329 7-pin connector, but soldering DIN connectors is a hassle. You could also buy the cheapest C-64 power supply you can find on Ebay. With some luck you should be able to score one for $15. For the power cord, you can simply buy a cheap extension cord and cut off the end that doesn’t plug into the wall.

When you prepare your cables, strip about a quarter inch from the ends to use to connect to the terminals inside.

Mapping out your C-64’s DIN connector

build your own Commodore 64 power supply
Here’s the pinout from the power supply side for a Commodore 64. Other pinouts may differ because they show the pinout from the computer perspective.

Commodore didn’t use a standard color coding with its power supplies, so you’ll have to map out the wires. The top two pins on the connector are 9 volts AC. The pin closest to the bottom center is DC ground. The pin at the bottom right is +5 volts. Use the continuity test on your multimeter to find which pin goes to which wire, then label each. Don’t assume your wire colors map out the same as anyone else’s.

Lots of 64 power supply pinouts exist online. The one I provide is how it maps from the power supply connector itself. It looks different from the computer side. If you find other pinouts online, make sure you know what you’re looking at.

Preparing an enclosure

You can get a commercial enclosure, but I just used a 4×5-inch tin box. This saved me a good $10. I painted it black and beige so it goes well with a breadbin-style 64 and 1541.

You’ll need to drill holes in the back of the enclosure for your wires. I drilled 1/2-inch holes, then stuck a 5/16-inch grommet in each to protect the wires from getting cut by the sharp edges. Thread each wire through the grommet, leave plenty of slack to reach inside, then tie a knot in each cable so it can’t slip back out. This provides a strain relief.

If you can’t knot the cable, at least put a zip tie around it. But a knot is more effective than a zip tie.

Wiring up your DIY Commodore 64 power supply

Connect both the mains wires from the transformer and the black and white wires from your power cable. Polarity doesn’t matter on the transformer side; connect the black wire to pin 1 and the white wire to pin 2, and the green ground wire to pin 3.

On the DIN connector side, connect the two AC wires to the two free wires on the transformer. Connect the +5 wire to pin 5, and the DC ground wire to pin 4. DC ground is not the same as AC ground in this case, so don’t connect the green AC ground wire to the DIN connector in any way.

Testing your new Commodore 64 power supply

To test your power supply, plug it into the wall. I recommend using a GFCI-protected outlet if you have one available, just in case. The first time I wired mine, I had a short from not tightening one of the wires correctly, and the GFCI tripped quickly, providing a safe and effective way to find it.

Assuming you have no mishaps from short circuits, test the 9V AC and 5V DC outputs with your multimeter. You should get 9 or even 10 volts AC without a load, and a little over 5 volts DC, again, without a load. I’ve seen some switching power supplies read dead-on at 5 volts even without a load. That’s OK. I prefer 5.17 volts since that’s what Commodore power supplies output when they’re healthy, but I’ve run my 64 on 5 volts exactly and not had issues.

Leave the power supply plugged in a few hours, then test the voltages again to make sure they’re steady. Then your power supply is ready for the moment of truth. Plug it into a 64 and turn it on. If you did everything right, it’ll work. And it’s very satisfying to build your own Commodore 64 power supply and then see it powering your machine for the first time.

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