Technical help with an IBM Model M

November 15, 2007 8:29 AM

Can you help me repair my IBM Model M keyboard?

I've got an IBM-manufactured Model M, Part Number 51G8572 (the kind with the speaker in place, shipped with the RS/6000) from 1992 which I took apart to clean thoroughly. There was water involved, but it was used only to rinse off the black plastic plate on which the keys are mounted. Upon reassembly, certain keys behaved strangely, or not at all: the shift keys, the space bar, the enter key, backspace, and backslash. I allowed the keyboard to dry for a couple days, and everything worked perfectly again, with the exception of the shift keys. They produce uppercase letters and alternate characters as intended, but not before producing a backspace and carriage return for the left and right shift keys, respectively. In addition, the | ("pipe") character can't be produced. I was lucky enough to do some diagnostic testing with another 51G8572, and by the scientific method have narrowed down the problem to be in the steel/plastic key matrix assembly or in its flat flexible cable connection to the printed circuit board. The PCB is fine. As you might imagine after all this writing, I'd like to continue using this keyboard and would rather not buy another one. And sending it to Unicomp for repair would end up costing more than a new keyboard.

Does anybody have a diagram of the key matrix or circuitry involved to help identify how the shift keys are related to backspace and enter? Could the problem lie in the physical contact between the flat flexible cable and the PCB? Perhaps it's been unplugged and plugged in too many times? Would it be a good idea to trim off a little bit of the cable? Any other help would be much appreciated.

posted by danb to computers & internet (3 comments total)

Here's a picture of part of the key matrix.
posted by zsazsa at 8:52 AM on November 15, 2007

Sounds like the wide keys aren't working right, and from my recollection all of these keys have a kind of leverage spring that has to be accounted for when reassembling.
posted by rhizome at 10:01 AM on November 15, 2007

Why not buy another model m keyboard on ebay? Cheaper than unicomp, plus you'd get the real thing (unicomp keyboards may use buckling spring, but feel considerably different from the original model m keyboards - lighter, fluffier keystrokes and it doesnt even make the same ka-thunk! sound (unicomp makes more of a clickity-clack! sound). Not the same. At all.
posted by jak68 at 2:14 PM on November 15, 2007