The IBM M keyboard is probably the most awesome keyboard every made. You could hit someone upside their head with it and continue typing. Unfortunately, IBM sold the rights for the Model M to Lexmark in 1993 and the quality of the board went downhill. This makes it harder and harder to find replacement parts for it and they eventually break down (albeit after 17 or so years).
I found this specimen at a rummage sale, the proprietor didn't know if it worked so I got it for $2 USD.
I took it home and discovered that it did not. If broken, what’s the harm in trying to fix it? First thing I had to do was get it apart. It takes a 7/32" screwdriver to get the screws out.
After removing the back and front cover I found the source of the problem, the spring board was attached to the metal plate with little plastic studs melted down to disks onto the metal plate. Overtime the disks must have deteriorated and knocked off with all the jostling it got over the years. I numbered all the places where a disk was located and peeled off the rest of the disks. Then I drilled 7/32" holes through the holes in the metal plate into the spring board, careful not to drill through or damage any of the important bits of the circuit sheet or spring board.
Here is a picture of the circuit sheets. It kept separating so I taped the two sheets together.
The rubber sheet protecting the circuit sheets form the springs.
The spring board with springs in it.
The Buckling Spring.
When I tried to reassemble it I kept running into a problem, the springs moved from the position they needed to be in and shifted out of place. To counteract this I pressed the springs into the key holders on the plastic spring board.
I used 10mm long Phillips-head countersunk M3 screws and regular hex nuts to reattach the components together. I found it best to screw it so only half a thread is visible above the hex nut. Any tighter and the keys get squished together and will tend to stick keys together when typing.
Countersunk screws were used because rounded head ones would push out the metal plate and spring board from the back cover. I couldn't even use countersunk screws on the bottom row (hole 52-59) because of this reason.
After assembly I flipped the springs back to their original position and attached the keys, testing each one as I went along. I could easily tell if a key wouldn't work if it didn't sound right when I depressed it, but just to make sure I reattached the keys with the keyboard connected to my computer.
The only thing left was to reattaching the front cover and I was finished. If anyone else would attempted this following this as a guide here are a few things I would do differently.
+ Use 14mm long M2 screws and locking hex nuts.
+ Wash the spring board, front and back covers, and metal plate before reassembly.
Things I may do in the future to this keyboard
+ replace the circuit board for Native USB support
+ paint the spring plate, and the front/back covers
+ replace the Num, Caps, and Scroll Lock LEDs to better colors (Any suggestions?)
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