Sunday, February 22, 2009

Model M Repair

I own 4 IBM Model M keyboards. I paid $5 each for them at a PC recycling store in Seattle. Of the 4, 3 worked with no problems. They were dirty, and I figured to use the 4th as spare parts. There is a ton of good information about cleaning Model M's on the internet, so that wasn't much of a problem. However, recently the "B" and "N" keys quit working on the one I was using at work. I found this excellent page that goes into some detail on separating the keyboard even further than necessary for just cleaning.

While these instructions were great, I wanted to make a few notes about some of the details.
  • Cutting off the plastic rivets is best done with a hammer and wood chisel. They pop off cleanly. My first thought was to use my Dremel, and while it worked, it took longer since it tended to just melt the rivets.
  • Once the metal plate is separated, again use the hammer and wood chisel to knock off the rest of the rivets. Again, quick and easy.
  • I didn't use any nuts and bolts, only screws. Since I'm in the USA, finding the metric screws is a little harder, and actually, I found that using regular #6 wood screws 3/8 inch long worked perfectly. I used 56 of these screws.
  • I used a 3/32" drill for the pilot holes. I drilled them on a drill press. I thought I'd need some sort of jig to handle the curved plastic, but it actually isn't that curved and can be pushed flat while drilling.
  • Before completely reassembling the keyboard, check the keys. I found that I had tightened a few of the screws a little too tight, which caused some keys to rub. Loosening the screw between the rubbing keys let them separate.
  • The problem with the "B" and "N" keys was that the conductive paint had corroded, so there was no longer a connection to the rest of the matrix. You can buy a paint pen from Radio Shack, but they are messy. For about the same price, I bought a roll of 3M copper adhesive tape, part number 1181. This tape cuts easily with scissors and sticks onto the plastic keyboard matrix.
  • I checked all of the routes on the keyboard matrix on both sheets with a multimeter, and ended up fixing one other spot with the copper tape. I'm glad I did that before I got it all reassembled.
  • There are 101 buckling spring pieces in this keyboard, and 102 places to put them. The place that doesn't need one is the left post of the space bar.
The keyboard is now working just like new.