A new "Click keyboard" for my Zx Spectrum 48

What you will find on this page:
Replacing the membrane keyboard with real click pushbuttons is not a complicated job.
The transformation will be permanent and will allow you to keep your original case and feel for the rubbery keys, but these will now click under your fingers and ensure a much longer life of your dear Spectrum. Of course you need some tools and the generic ability to take apart and reassemble your computer without damaging it. Also you will need to desolder the original keyboard connectors and have some wrapping-type wire and some perhaps some epoxy glue.

Pusbuttons like these can be found in many stores. I got a whole lot from old equipment that I have taken apart. VCRs have quite a few mounted on their faceplace. You could also try Mouser
You will need 40 pushbuttons like these, possibly all the same type and manufacturer so that the "feel" is the same for each key. I used one extra button connected to the RESET pin and hidden next to the "0" key.
(Only accessible through a pin hole)
This is where we start:
Take apart your ZX Spectrum and remove the keyboard. Hey, there's no reason to be nice to the membrane connectors since we're finally going to get rid of it at once! Gently straighten the metal tabs that hold the metal plate to the plastic case and release it along with the rubber keys.
This is what you are now working on. As you may faintly see, I have already drilled tiny little holes in the middle of each "key box", exactly in the center of the plastic little bump which is already there.
Now you can drill 40 holes of the EXACT same size as your replacement pushbuttons. Try it on a separate piece of plastic to make sure your switches will go in as tight as possilbe.
Squeeze them in from the back after you flattened the pins out to hold. After you have the whole set wired, you can use a bit of epoxy glue to fill the gaps and make the keyboard very strong.
The connections on the back are very simple. Each switch has 4 pins. If you look at them, the ones that look farther apart are already connected to each other, while the ones closer in are the ends of the switch. Use some sturdy wire to make 8 horizontal connections and some wrapping wire to make the verticals.
Wire your network by rows and columns like in the original layout. You need to connect 8 groups of 5 keys. This way you will end up with 13 wires to solder to the PCB in place of the old keyboard connectors.
Use your membrane keyboard as your template to ensure your lines match the original layout, or your keys will all be misplaced. In any case, you can't do any real damage to your machine.
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Well, that's pretty much all. Put the rubber keys back in place, then the metal faceplate, bend the tabs and you're almost done.
I twisted my 5 wires and the other 8 and soldered the lines to the PCB allowing a little extra for opening and closing. You can use male/female flat connectors if you plan to open your ZX often. That's up to you.
Enjoy your newly clickable keyboard!!!