VIC-20 2-Prong PSU Restoration

I like to keep an assortment of working power supplies for various vintage computers in an accessible manner, alongside all my test equipment, so I can easily power up pretty much any computer or board that I might need to.

Most of the spare power supplies I use have been bought alongside computer bundles that I’ve bought, and this one was no exception: a 9Vac PSU for an early Commodore VIC-20. These are tricky to come by as they are generally discarded, and there are no modern-made equivalents as the power connector on the computer is proprietary. Ironically, it came alongside a Commodore 64 bundle, and not a VIC-20.

VIC-20 2-prong PSU in its original condition.

Therefore, despite being in poor and non-working condition, this one was worth refurbishing. The first problem was that it had been fitted with a DIN connector on the output side (for what purpose, I couldn’t possibly say), the second that it had a cracked fuse holder, and the third that it was disgustingly dirty.

The first problem was tricky to solve because, as I mentioned before, the connector is proprietary, and even differs between the UK and the USA. I was able to find a 3D-printed replacement online, which I soldered into place – the outer cable insulation was too thick to fit inside the connector, even with some filing down, so I fitted some black heat-shrink to cover the step instead.

The second problem was worse than I’d imagined – the previous owner had the genius idea of replacing the fuse with a piece of cut-down studding, which, coupled with the 13A-fused plug, could have happily caused a fire had the transformer shorted.

The original “fuse”.

I managed to steal a suitable fuse holder from one of my spares 1541 FDDs, then fitted a suitable glass cartridge fuse (T200mA).

The third problem was an easy, if time-consuming, fix – a good scrub with Cillit Bang. Often, PSU cables get coated over time with a layer of what resembled dried-up PVA glue, which is actually deteriorated polystyrene from the packing box, and needs picking off.

I fitted a new UK plug (3A fused) and tested the PSU, first with a multimeter, then with one of my early VIC-20s, and all is now well. A successful rebuild for a PSU that should have ended up in the bin, for around £7.00 all-in – bargain!

Published by themightymadman

A conscientious, intelligent and committed graduate engineer, with excellent interpersonal skills, an eye for detail and a keen interest in hardware design, mathematics, and software development.

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