ZX81 with mismatched ROM, jumper cable and flat cursor

[Moggy]

Bit by bit it's getting there, nice one.


The keyboard membranes Mark points to are very good replacements and have a more solid pair of ribbons than the original.
One thing I have discovered with them is that once fitted leave them fitted as at end of the ribbon there appears to be some sort of conductive "carbon" like material which, as I found to my cost, won't stand repeated connect/disconnect as it wears away this material very quickly rendering the ribbon useless and unlike the original cannot be cut back to rectify.

An alternative to the membrane can be found here and I thoroughly recommend them.

https://www.ginger-electronic.com/en/

[nicad]

Thanks again both, yes getting there!

I connected various pins from one connector to the other and as if by magic, text appears! Knowing the keyboard or cable at least is bad, I thought I might as well cut the scrappy ends off the cable and give it a go. I did once get a couple of numbers, but nothing else. Then in the process of cleaning and retrying, split the cable

So I've ordered the first recommended replacement, though I'll possibly upgrade to the Ginger version if that fails at any point in the future.

Still, I've got a cool sticker now

[1024MAK]

Ahh, removing the existing keyboard membrane is always "fun"

Mark

[Moggy]

Ahh, removing the existing keyboard membrane is always "fun"

Mark

When all the usual goo removers fail I use this. (As recommend by Lardo.)

[Lardo Boffin]

Ahh, removing the existing keyboard membrane is always "fun"

Mark

When all the usual goo removers fail I use this. (As recommend by Lardo.)

[nicad]

It lives!

The new keyboard arrived, fitted, and all keys worked first time - the old keyboard goo wasn't that hard to get rid of in my case, guess I was lucky or somebody had replaced it previously?

Whilst tinkering, I also fitted a ZX-WESPI (minimal version), replaced the regulator and created a USB-C PD 9v cable adapter to save having to use the original power block.

The only thing I'd like to do now is to upgrade the RAM internally to 16k so I can keep the exterior uncluttered. There is this option from ebay https://www.ebay.co.uk/itm/256060383699 ... UwQAvD_BwE but it talks about removing the two original chips so not sure if that will be compatible with my single chip setup? There is also the method linked to on https://www.sinclairzxworld.com/viewtopic.php?t=4358, which looks like a bit more effort, but does mention the single chip variant. Any thought on compatibility or recommendations?

Thanks for all your help so far, very much appreciated!

[1024MAK]

Good that it's now fully working

In my blog some years ago I detailed a 16K byte internal RAM modification (with provision for 32K byte at a later stage) here.

If you are not confident with track cutting, elsewhere there is details of achieving the same thing without any track cutting. Instead various pins are bent out and individually wired up with thin insulated solid core copper wire.

It works well with the older 32K byte SRAM chips. If you use one of the currently available (faster) modern SRAM chips, an extra ceramic capacitor may be required so that hi-res programs/games/demos work correctly.

In all cases, the existing single large SRAM chip or the two existing smaller SRAM chips have to be removed. If you are not good at desoldering, you can cut all the legs. Remove the chip body. Then it's far easier to desolder and remove the individual pins. Whatever you do, don't use force when removing pins, as you will damage the PCB pads, tracks or through hole plating.

Mark