Is the Commodore 128 power supply safe to use?

Last Updated on April 23, 2023 by Dave Farquhar

Commodore 64 power supplies are notoriously unsafe to use. As a result, all Commodore power supplies have a bad reputation. I won’t say it’s unfair. But it means questions about the Commodore 128 power supply come up frequently on vintage computer discussion groups. Is the Commodore 128 power supply safe to use? The short answer is yes. Here’s why.

The Commodore 128 power supply was designed to be safe

Is the Commodore 128 power supply safe?
Thanks to engineer Bil Herd’s better judgment, the Commodore 128 power supply is much safer and better designed than its C-64 counterpart.

The Commodore 128 power supply’s design is completely different from the C-64. Bil Herd, the chief engineer on the C-128 project, had a mixed track record when it came to following orders. He designed it to be safe, repairable, and reliable. Among other things, management told him not to put a user-replaceable fuse in it. Herd claims he doesn’t know how the power supply got one. Sure, Bil, tell us another story.

Unlike the stock C-64 power supply, the C-128 power supply isn’t potted in epoxy. It’s hard to open, but you can open one up if you choose the size of screwdriver you use carefully. And when you get inside, you can see the components. It runs cool, it’s designed to power a fully upgraded machine, and most importantly, it doesn’t fail catastrophically. It can fail, but it doesn’t fail in such a way as to overvolt the machine and damage bespoke out-of-production chips inside.

Some 128 power supplies were assembled using some questionable glue that becomes corrosive over time. Those power supplies will fail, and not operate the machine properly. But they won’t overvolt the machine. They just make it act funny, or fail to power up at all.

Commodore power supplies have a mixed track record, and deservedly so. But the 128’s supply was one of their better efforts.

Commodore 128 power supply repair

An experienced technician can fix a Commodore 128 power supply. But I’m certainly not qualified to teach you how, and I think the people who know me well would question how much business I have in trying to fix one myself.

If I had a failed 128 power supply, I’d replace the components rather than trying to rebuild it. The approach I took with my DIY C-64 power supply applies. Just make sure the 5V switching power supply you use can provide at least 4 amps, and use the cables from your 128 supply. My 128’s power supply was rated at 4.3 amps on the 5V side, so it would be better to go with 4.3 or 4.5 amps. A 4.5 amp unit may be easier to find today.

But unlike the 64, you’re unlikely to permanently damage your 128 by plugging it in just to see if it works. If you’re unsure, I’m glad. You can test it with a voltmeter. If you plug it in, you should find 5V DC on the bottom two pins (holding the plug with the dimple facing upward), and 9V AC on the center pin and the pin in the upper left. If you detect low or no voltage on either of the pin combinations, you need to either build a new one, or buy one. Several people sell replacement C-128 power supplies on Ebay. The Electroware supplies made in Poland have a good reputation.

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