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Author Topic: IBM Model M membrane issue  (Read 2426 times)

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Offline lukaus

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IBM Model M membrane issue
« on: Wed, 20 June 2018, 10:20:15 »
Greetings!

 I recently attempted to restore a 1999 IBM Model M 122 keyboard I got off eBay by doing a bolt mod and wiring it to a Teensy++, but I have run into a problem:

While working on the key mapping with QMK, I've noticed that sometimes pressing one key will cause the keys around it to register too, despite not being pressed. I've tried reseating the key stems, but that doesn't seem to help. I've also noticed that the effected keys 'move', as in a key that does this might eventually stop and another one start.

This leads me to believe the membrane is what is causing the trouble. The barrel frame was pretty badly warped when I got it; the bolt mod is helping with that some, but the membrane did not lie flat when I was reassembling the board. It had large 'bubbles' in it, for lack of a better term; places where the membrane did not lie flat against the barrel frame and metal backplate. I believe this 'warping' is likely causing the membrane to make contact improperly, which I think would explain the key overlap as well as why the effected keys seem to move around the board.

I'm really hoping to get this board working, and was hoping someone had any thoughts as to potential solutions, or any thoughts about other things to look at that might be causing this problem.

Thanks!
Lukaus
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Offline lukaus

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Re: IBM Model M membrane issue
« Reply #1 on: Wed, 20 June 2018, 10:20:56 »
aaaand i posted this in the wrong board  :'( sorry
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Offline fohat.digs

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Re: IBM Model M membrane issue
« Reply #2 on: Wed, 20 June 2018, 11:51:00 »
I can't imagine what you are describing. The bolts should match their holes in the mat and this should not allow any more than an inch without a forced alignment.

This seems like a strange problem - I recommend that you take it apart and put it back together.
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Offline lukaus

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Re: IBM Model M membrane issue
« Reply #3 on: Wed, 20 June 2018, 12:13:12 »
The holes all line up, its like the membrane doesn't match the warped curve of the barrel frame so won't lie flat against it.

I'll reassemble it and see if I can take a video of what I'm trying to describe if that doesn't help.
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