Sunday 17 September 2023

Commodore PET Keyboard Repair / Refurbishment

One from the Patreon Exclusive posts archive - a Commodore PET 8032 keyboard repair.

This is the keyboard from the PET 8032 as it arrived.

Looks like that needs a bit of work.

And a shift lock key, as that seems to be missing.

First job, strip it down and clean it up.

One of these things is not the same.

You might notice a yellow key at the top. This appears to be the return key from an early VIC20.

It looks very brown in the photo, but in normal lighting, you barely notice it.

Oddly my test keyboard also has a replacement return key, although mine was from a BBC mirco keyboard. (

With everything cleaned, time to address the shift lock.

I didn't have a PET keyboard for spares (or an early VIC20 with the same style keyboard), so I went for the shift lock key from a normal VIC20 / C64 keyboard. I was hoping it would be a drop in replacement.....

The only problem was it was too small to fit in the hole, clearly the earlier switches were larger.

My solution was Sugru. If you haven't come across that before, it's basically blu-tak that sets hard like rubber. (you can also remove it later if someone finds an actual PET style shift lock key)

I padded out the smaller shift lock switch with black Sugru and left it to dry.

The top side wasn't as neat, but still functional.

You get about half an hour before it goes off, so I fitted the keys either side to align it to them.

It is a different height, shape and colour, but you don't notice that normally.

I left that for several hours to go off, and then fitted the rest of the keys.

Normally, the pins of the switch poke out of holes on the back of the PCB, but with the switch being smaller, I had soldered them to the switch before I fixed it in place.

They then solder to the pads near the connector, where they are wired directly across the position of the normal shift key in the matrix.

All looking good, and just like the return key, you don't really notice the brown of the shift lock in normal light.

And with that, the keyboard was complete and ready to reunite with the rest of the PET.

I find it useful to test with one of my USB keyboard controllers, this proves the keyboard work, and any keys not responding just need to be run in, rather than a fault with the 6520 or the 74LS145 that drives the keyboard.

Some of the keys take a bit of pressing to register. They normally come back with use, but I haven't found a good solution yet to make them more responsive. There are various concoctions you can paint on the contacts, but they don't seem to last long.


PET USB keyboard controller / keyboard tester

As mentioned above, I use the USB keyboard adapters for testing keyboards.

All of these have jumpers to select business / graphics / chiclet keyboards.


I have a "universal" board which has a 20 pin connector for most keyboards and a 25 way D for 80xx-SK keyboards.

20 pin only

There is also a version without the 25 way D, if you don't need support for the 80xx-SK keyboards.


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