At the time of this writing (2023), the keyboard "membranes" of the few remaining 1988 Schneider Euro PCs are, most likely, pretty much fully deteriorated - a nightmare for vintage computer enthusiasts trying to keep these machines alive. Restoring a Euro PC's keyboard is one of the biggest challenges in keeping these nice vintage machines fully functional.
Technically, the Euro PC keyboards are not really "membranes" - they just consist of a single sheet of Mylar with traces and button contact zones made of conducting paint. The keys are metalized rubber "stamps" that close these contacts on the Mylar sheet. So it's more appropriate to call the Euro PC keyboard a single-layer conducting Mylar "sheet" keyboard instead of a membrane keyboard. I'll use the term Mylar sheet keyboard in the following.
Whereas it is possible to repair the traces and contact zones on the Mylar with conducting "leitsilber" paint, the worst part of this keyboard is that the Mylar sheet just gets extended and turns into a flex cable that then connects directly to the motherboard via a simple flex cable connector. The metalized end contacts of this Mylar flex cable are pretty much impossible to repair once they deteriorated. Moreover, the spacing of the conducting paint traces is very fine and narrow, making repairs with Leitsilber almost impossible, and the flexcable part of the Mylar sheet cracks easily in this region as well. A real nightmare.
To once and for all get rid of the Mylar sheet in the Euro PC keyboards and repair your original Euro PC keyboard, I created this flexible (0.4 mm thick) PCB as a substitute. Just open up your EuroPC keyboard, remove and dispose of the Mylar sheet, and put in this flexible PCB instead. You may have to use an exacto knife to carve out some extra material from the PCB to make it fit perfectly with the keyboard carrier plastic posts.
Also, the flex cable connector on the Euro PC motherboard needs to be removed (by desoldering it). It is then replaced by a little adapter board. Single row standard pitch header pins connect the adapter board to the motherboard. Fine pitch pin headers on the adapter board are used to connect it to the keyboard, using a female, fine-pitch (IDC) ribbon cable. The keyboard PCB has proper fine pitch pin header mounting holes as well. See the pictures below for illustration.
YouTube Video - Euro PC keyboard repair notes.
I used https://jlcpcb.com/. The specs are as follows:
It's a normal 2-sided PCB, not a "Flex" PCB! Just use the default values on the JLCPCB website, but change the PCB width to 0.4 mm! That's all that is required.
The Gerbers for the (0.4 mm width) keyboard PCB as well as the motherboard keyboard adapter are in the Gerbers directory.