IBM Model F XT: Dirt ingress and reliability

Coeus

17 Sep 2021, 00:40

Earlier today, I noticed a small piece of lettuce between the keys of my IBM MOdel F XT keyboard. I held the KB upside down and shook to get it to fall out, which it did, but then afterwards I found the P key had stopped working. Removing the keycap I could wiggle the spring to make it work but it would never work with the keycap on.

Eventually, I concluded I would have to dismantle the KB and clean it. As well as cleaning the case and keycaps I also took the sandwich apart and cleaned the barrels, flippers and PCB. Interestingly, the PCB had debris on it, which may well have been the cause of the trouble, that was not there the last time I had assembled it.

I am now wondering how it got there and, in particular, if holding the KB upside down would promote this. Obviously debris can fall between the keys but how would it get from there onto the PCB? Inverting the KB could let it fall into the underside of the keycap moulding but get from there to the PCB it would have then fall down the barrel and get past the flipper, but perhaps that is possible.

Anyway, after a clean and the fishing line trick to hold the space bar flipper in place during reassembly, it is now working again.

Interestingly, I had to do a little bit of typing on a rubber dome extended layout keyboard why I was waiting for parts of the Model F to dry and found it hard to keep my hands in the right position. We do, of course, just get used to things and I found the same when I first got the Model F, but when you compare them the standard letter and puctuations keys are much more central on the original XT layout, with function keys to the left and the keypad to the right. In the extended layout the standard keys are all the way over the to the left and, on the right, there are the cursor keys and insert/home etc. so the keyboard needs to be moved a fair bit to the right to have your hands in front of you when typing.

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