IBM model M's non-working keys diagnostics

[okrutnik]

So recently I buried among my lengthy ramblings and impressions ( ) a problem and a question:

'e' and 'i' alternate between not working and chattering when I hit them harder. I connected the "clock" wire somewhat suboptimally, but all the other keys work fine, except for the right arrow and 'z' which don't work at all. I noticed that keys contact better when I make sure that the spring is mounted at the center and whines loudly on pressing, but it doesn't help with those four. I wonder if it means I would need to disassembly the backplate, clean the membrane and bolt-mod the thing. (Should this help?)

Since then I made some research and tests on my own. It seems that many people have (superficially) similar issues:

• single keys not working, but fixed by remounting keycaps & keystems

As I said, there are places where it didn't help.

• keys not working in a cluster -> black plastic rivets holding the backplate together may be broken and the plate is too loose, in need of bolt mod

Clearly not the case here. The rivets are so well preserved it's almost sad.

• keys not working alongside a path on membrane -> electric path not working, need to retrace the path, or replace the membrane or controller (depending on what is causing this problem)

This also not the case. [I think a proper guide to fixing these common issues would be useful, hopefully written by someone who've had >1 Ms in their hands. There are imgur guides which are basically "how some guy restored his first IBM".]

So it seemed that I exhausted my possibilities and was left to try tinkering on my own.

I was able to actuate some faulty switches (ie. get characters on the screen) by pressing their hammer plate inside, which is normally pressed by the buckling spring.

It's probably better to use a plastic lollipop stick, since it's thinner and can't leave splinters.

So it's clearly a mechanical issue: bad switches. Hammers don't actually hit down properly, and you can even kinda hear it: the keys sound more hollow and less high-pitched. I noticed that some of them are rusted a little, but again some rusted switches work. Anyway, I treated them with lube meant for car locks (it contains isopropanol, which is the thing I somewhat counted on). On the nastiest switches the rust colored the Q-tips red.

Yuck.

In case you're wondering, three sessions of lubing also didn't help. OK, technically now the right arrow works very occasionally. (Isopropanol does work nice for removing marker writing from the plastic case). It seems I'm admitting defeat for now.

I made the keyboard usable for playing around by enabling "bounce keys" in the OS (it's in accessibility options, helps with chatter) and a few clever remappings, but I think I will need to replace buckling springs to really make use of it. This will be a larger project. Brand new buckling springs with plates can be bought from Unicomp I think.