IBM XT Keyboard -- Dead Key

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Hypersphere

13 Apr 2014, 01:09

After removing the case from my IBM XT keyboard, cleaning, and reassembly, all the keys work except one: the "a" key (to the left of Ctrl). I did not separate the metal plates during this operation, and I did not place the assembly with springs down on a surface. When I had the assembly upside down, I supported the ends on two thick books to protect the springs.

I have tried pulling the nonworking key and reinserting it, being careful to have the spring aligned properly, but the key fails to respond. I have also tried other spare keys and swapping with working keys on the XT board, all to no avail. As you know, the XT keyboard is a capacitive buckling spring mechanism, and the switches are expected to last even longer than the membrane BS switches found in the Model M.

Suggestions welcome on how I might get the defective key working again.

Thanks.

quantalume

13 Apr 2014, 03:37

Does the key click but just not register? It's possible some dirt fell into the barrel while you had the key off. I would take the key off again and invert and shake the keyboard. If you have a can of compressed air, shoot a little in with the keyboard inverted.

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Hypersphere

13 Apr 2014, 16:09

Last night I found that by gently pulling on the spring and releasing it, I got registration of "a" on the computer. Finally, the key started working again. This is good, but I am not sure why it stopped working or why it started working again. Your theory about dirt in the barrel looks probable. Thanks.

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fifted

13 Apr 2014, 19:25

Scary! Mystery of the dead key... Glad to hear it's working again. FWIW, I'd agree re: dirt. That's happened on mine once or twice.

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Hypersphere

14 Apr 2014, 18:50

I asked Clickykeyboards.com about the temporarily dead key issue. He said that he has encountered similar behavior with XT and AT keyboards. It seems that the capacitive switches in these boards are especially sensitive to moisture. If you clean the boards and/or their keycaps and put the caps back on before they have thoroughly dried, moisture can reach the switches, temporarily inactivating them. After an affected switch dries out, it starts working again.

Upon mentally reconstructing what had happened in my case, I realized that I had put the caps back on the keyboard before they were completely dry. Thus, the moisture inactivation theory seems like a very reasonable explanation, and it indicates that care should be taken to let washed keycaps dry completely before putting them back on the keyboard.

quantalume

14 Apr 2014, 19:29

That's good to know. Putting wet/damp keys back on is also not a good idea because those springs will rust. I usually use compressed air to blow out the water that gets trapped and then let the keys set a whole day to dry before reassembly.

User avatar
Hypersphere

14 Apr 2014, 22:53

quantalume wrote:That's good to know. Putting wet/damp keys back on is also not a good idea because those springs will rust. I usually use compressed air to blow out the water that gets trapped and then let the keys set a whole day to dry before reassembly.
I agree. However, be careful of your compressed air source. If it is from an industrial air line or shop compressor, the air could be contaminated with oils. "Canned" air should be clean, but because expanding air through a nozzle results in cooling, the cold air can cause condensation of atmospheric moisture on the exposed parts. Nevertheless, definitely, it is a good idea to let the caps dry thoroughly before reassembly. I was too impatient. Haste makes waste!

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