But it could be that two of the wires are +5v and ground and one address line.

In the first picture i think that part of the switch stopped working , so the fuse is there instead of the switch. Replace it with a new switch and you will be ok. As for the second one , do you have a picture of the switch body? One of the wires will be ground and the other two will be upper addres...

Glad to hear it!!

According to this site D1 is U9 not U12??

https://myoldcomputer.nl/technical-info ... 5-01-c64b/

I am assuming that you have swapped the ram chips around to see if the error follows either u12 or u23 and have checked for data bus shorts to ground with a multimeter? The results you are getting would indicate to me either a ground short on D4 ( u23 data ) or more likely a short between D1 and D4 ...

The vic20 and C64 keyboards are exactly the same pinout .
I know this from my keyboard project on here!

viewtopic.php?t=15160

sorry m8 that link is five years old , most usb now will not work.

Just for the people who are interested the AE on the part no. is the designation for 28 pin dip and if it has a 1 on the end ( i.e. MT8808AE1 ) it is a 'lead free' part ( no Pb ) and , supposedly , better for the environment .

It might be worth asking mouser as they do not appear in the catalogue but i can get a page up with the MT8808AE1 that shows 17 in stock. https://www.mouser.co.uk/ProductDetail/Microchip-Microsemi/MT8808AE1?qs=pU29NIZ4ZwDlQSPjr7ESlQ%3D%3D mouser sku is 494-MT8808AE1 and here is a list of suppliers w...

That does not apply to modern usb keyboards , only the early one's that work with the USB to PS/2 adapter have the PS/2 protocol and will work. In the early days of USB they needed a way to be compatible with the PS/2 protocol as the majority of computers still had them , that is why they shipped th...