One of my 800XL keyboards with the mylar sheet unfortunately decided to crack right across its width at the keyboard end.
Ordered the new mylar from retrohax_de and waited for it to arrive. And that is where the fun started.
I carefully folded it over, with the separating sheet between and tested it before fitting it to the keyboard, and all worked well.
Fitted it to the keyboard mechanism and absolutely nothing. I couldn't get into the self test, and trying to type from the ready prompt wouldn't work either.
Took it apart and carefully tested it again, and it worked.
To cut a very long story short, (about 6 hours of frustration), I compared the old separator against the new, and there is no physical difference that I can see. So just on a hunch, I used the old separator sheet with the new mylar, re-assembled the keyboard and all works well. A fully functional 800XL at last.
Now for a sit down, and a coffee.
Stay safe all