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Model M With Overly Sensitive Keys?

tempest

tempest

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I have an IBM Model M keyboard (71G4644 non-clicky Lexmark) that I'm using with one of my systems, but it seems to have developed a problem. The semicolon key (and to a lesser extent the apostrophe key next to it) are way too sensitive. If you merely brush against the key it triggers. I can barely touch it and wiggle it and it will trigger. None of my other keys do this so I'm wondering if the membrane underneath needs to be cleaned. I went to go crack it open, but it appears to use some weird sort of security screws that are pretty recessed in a small hole. What's the secret to opening these and does my problem sound like a dirty membrane?

EDIT: I managed to get it open but it was pretty clean inside. The rubber dome under the key looked ok, but I blew it out to make sure there was no extra crud under it. Unfortunately I don't see a way to actually clean anything under the keys.
 
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Sorry, the only M's I've ever seen are the buckling-spring types. Betcha customers were really put out when they found that the Model M that they were getting wasn't anything like the old ones.

But yeah, these were the later "Quiet Touch" keyboards. I have no idea how to repair these, particularly without removing the membrane. They mostly seem to be a source for parts for the mechanical model M keyboards, as the keys are interchangeable.

I use a couple of the IBM rubber-dome IR keyboards; the feel is decent (certainly better than a lot of garbage out there) but that's the limit of my experience with these.
 
I'm sorry; I can't resist the temptation to say that if the keyboard seems overly sensitive, perhaps it would benefit from counseling. :rolleyes:

robots at marriage counselor c887b470f772112e683729d97c3bc684.jpg
 
I have a second rubber dome Model M that's doing the same thing but with the 5 and ] keys. I'm guessing that the membrane under the dome is damaged or gunked up somehow, but I can't see an easy way to get to the membrane. Maybe those rubber domes just break down after a while? I guess I might as well try and sell them for parts or something like you said as having spurious key presses isn't exactly something you want when typing. It's not the best, but I have a NIB (baggie anyway) Dell Quiet Key PS/2 style keyboard that I found in the back room at work that I can use with my PCjr. It's still light years better than the PCjr original keyboard.

Bill-kun said:
I'm sorry; I can't resist the temptation to say that if the keyboard seems overly sensitive, perhaps it would benefit from counseling.
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Nice. :)
 
Well, rubber (broadly speaking) does break down with time. Given that the rubber-domed Model Ms are what, 25+ years old, that's a definite possibility.

But PCJr? Did you see my posts on the IBM IR keyboards that can be had for as little as $2.50 NIB? All you need is a "blue pill" with optosensor and a cable. to get those to work.
 
Chuck(G) said:
Well, rubber (broadly speaking) does break down with time. Given that the rubber-domed Model Ms are what, 25+ years old, that's a definite possibility.

But PCJr? Did you see my posts on the IBM IR keyboards that can be had for as little as $2.50 NIB? All you need is a "blue pill" with optosensor and a cable. to get those to work.
Click to expand...

No I didn't. Link?
 
Have you ruled out a physical problem with the keycaps themselves (maybe the keystem is constantly making contact with the rubber dome, causing the unwanted keypresses)?
 
I looked but didn't see anything. I sanded the bottom of it just in case but it didn't seem to make a difference.
 
Does the rubber dome look cracked or feel brittle at all? If so then the rubber dome may have just broken down over time like Chuck said. If this were a case of the rubber domes breaking down over time you would think this would be happening to more than two keys though. How about any signs of melting/heat damage?
 
TH2002 said:
Does the rubber dome look cracked or feel brittle at all? If so then the rubber dome may have just broken down over time like Chuck said. If this were a case of the rubber domes breaking down over time you would think this would be happening to more than two keys though. How about any signs of melting/heat damage?
Click to expand...

No it looked just fine. I poked at it a few times and it moved just liek you'd expect it to. No cracks or anything structurally wrong with it. The dome and membrane underneath (as far as I could tell) looked fine.
 
There indeed were rubber dome Model M keyboards. It's actually not drastically quieter than the standard buckling spring version -- the keys still generate a fair bit of noise when typing.

 
So how hard is it to remove the black tray under the keys to get to the membrane? I didn't see any easy way of doing that, but I didn't want to start prying at random things either.
 
tempest said:
So how hard is it to remove the black tray under the keys to get to the membrane? I didn't see any easy way of doing that, but I didn't want to start prying at random things either.
Click to expand...

Since I don't have the keyboard in question, I can only presume there are no visible screws and maybe there are some tabs or something that hold the tray in place?
 
TH2002 said:
Since I don't have the keyboard in question, I can only presume there are no visible screws and maybe there are some tabs or something that hold the tray in place?
Click to expand...

I suppose I can try, it's not really usable in its current condition anyway.
 
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