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Repairing or replacing the Mitsumi keyboard?

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I just acquired a TI-99/4a system and all seems well, except that the majority of the keys don't work, or don't work every time. Turns out that this beige TI-99 has a Mitsumi keyboard.

 

I'm going to try and repair the mylar. Any suggestions? It pretty much seems like a lost cause as the mylar is "stuck" to the pc board.

 

Are there replacement keyboards for these machines to be had anywhere?

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There are a couple of options for replacement keyboards. Sometimes NOS keyboards show up for sale on eBay, but a majority of those (in the Radio Shack packaging) are Mitsumi keyboards, which won't help much unless the keyboard is one of the other types (about 30-40 percent are other types). Some used keyboards also turn up (just watch out for the Mitsumi types). Any of the non-Mitsumi boards can be safely used in any /4A. There are also several PC-style keyboard adapters (for XT, AT, PS2 (IIRC), or USB keyboards). Recently, discussion has also focused on the possibility of building new keyboards with modern switches (but that option isn't cheap or even available yet).

 

One or two folks have successfully rejuvenated a Mitsumi keyboard. There is an existing thread on the process here (and the FAQ may even point to it). It isn't easy--and that mylar is really easy to tear. . .

 

I have a whole case of original keyboards that I bought about 20 years ago--but they are ALL Mitsumi boards, so I haven't been able to use them for their intended purpose.

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I successfully restored my Mitsumi keyboard. It was not fun as the white layer under the mylar did not want to let go of the pcboard. A good scrub with DeOxit and some foam tape behind the row of contacts connecting the mylar to the pcboard seemed to do the trick. No idea for how long though.

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