Sources for 8b TTL keyboards (Keytronics)
jzg22 at drexel.edu
Mon Dec 8 12:36:27 CST 2008
>It's been interesting taking out my old CP/M stuff and getting it
>My system uses an 8bit TTL Keytronics Capacitive Sense keyboard. It was
>operational for about an hour and then it quit.
>It turns out that the keyboard uses little sponge pads to hold the
>capacitive disks and they have biodegraded into dust.
>So I went looking for an old 8b TTL replacement keyboard. So far no luck.
>I also looked for a black box solution that would take an AT or PS/2
>keyboard and convert it to a parallel port output. So far no luck.
>So let me turn to the experts and ask for advice and suggestions.
I have to deal with the same problem, but I read somewhere that its possible to repair the existing keyboard by replacing the disintegrated foam with doublesided-sticky 3m grey 'exterior?' mounting foam of approproate thickness, and that's what I'm attempting. Better IMHO to repair the old rare keyboards than replace with something new but 'incorrect' for a given system, though a new keyboard can be a temporary solution until the old one is fixed.
You basically take keyboard apart, remove all the conductive discs but don't throw them away, scrape the remains of the foam off the bottom of the key plungers (can use goo-gone to help with this too), punch new foam disks from 3m grey mounting foam, clean off the old conductive paper discs (also can use goo-gone to help here), carefully apply discs to foam, and stick new foam+old discs back onto each key plunger. Apparently you should use a qtip with a small bit of goo-gone around the edge of each new foam disc to prevent the top and bottom from sticking together and 'pillowing' the foam disc.
It may be easier to first stick the conductive discs to the foam and use the disc as a guide for punching the foam, that way it will always be exactly 'on register'.
The trouble is you need to buy a punch to punch the foam into discs of the same (or slightly narrower) size as the shiny conductive paper discs are (or have it shave a small bit off the edges off of the conductive discs, if they're a tiny bit smaller it shouldn't hurt anything I'd think). I have not done this yet, and am not sure where to buy an appropriate punch (art supply store didn't have it).
If any of the aluminized-paper contact discs are 'beyond repair', I have NO idea how to replace those. Aluminum foil MIGHT work, but it doesn't sound like a good solution because its TOO conductive, I think.
I have 4 keyboards that need fixing in this way:
one keytronic kb3270pc (1986 firmware)
four victor 9000 US-type keyboards (manufactured by keytronic)
Fortunately (unlike the old digital group keyboard keytronic made with its completely insane #-shaped contact pads) I believe all 4 keyboards use the same diameter paper contact circles and foam, so I should only need one punch.
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