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Author Topic: IBM Model M - Key does not register unless fully depressed  (Read 1639 times)

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Offline Cheemio

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IBM Model M - Key does not register unless fully depressed
« on: Sat, 04 August 2018, 19:59:48 »
Hi all,

Recently I bought a used IBM model M off of Ebay. It was manufactured by Lexmark in 1994. Overall, it's in pretty good health. Just needs a bit of cleaning up just like most keyboards of its age.

However, I have a weird problem with my right control, left arrow, and down arrow keys. The problem is that the keys do not register with the computer until they are fully pressed down the whole way. With buckling springs, they are supposed to actuate as soon as you feel the click. So it's a problem I really wouldn't like to deal with here. Do you guys think this is a problem with the springs, or the membrane itself? I haven't taken a look at the membrane yet, but I plan to take it apart for cleaning anyway so I'll be sure to look at it then.

Anyway, I was wondering if anyone else had this problem and any ways to fix it. I have searched around but it seems most people have problems with keys not actuating at all, instead of the specific issue I had.
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IBM Model M

Offline fohat.digs

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #1 on: Sat, 04 August 2018, 20:51:14 »
If the malfunctioning keys do not feel and sound like the others, you probably need to re-seat the key stems. Pull them off and carefully seat them back into place.
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"Starting in 2011, the deficits again started to shrink. During Obama’s term  the deficit was reduced by $900 Billion  before finally in 2015 the GOP managed to wrangle a “reconciliation” bill out of Obama where he again cut corporate taxes, as well as made permanent some of George W. Bush’s original tax cuts. This is the year everything reversed. Before this, under Clinton, Bush and Obama the deficit in almost every year was gradually decreasing. The balance we had of taxes and the economy was bringing the deficit down, the money coming in was slowly catching up with the money going out until 2015. Trump’s subsequent tax cut has continued the new trend even after the rest of Bush’s cuts have since expired. Obama had an average GDP of 2.3%, with 11.6 million jobs created and unemployment peaking at 10% in 2009, then falling to 4.3% in 2016. If we had continued on that downward deficit track, we would have again reached balance and another surplus in 2017-2018.
– Frank V Walton 2025-07-01

Offline Cheemio

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #2 on: Sat, 04 August 2018, 21:19:07 »
I have tried reseating them a few times, the issue still persists. It is true that these keys sound different than the other ones, though. Maybe they need new springs?
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Offline pixelpusher

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #3 on: Sat, 04 August 2018, 22:20:56 »
Sounds to me like the plastic rivets in that area have all broken and now the capacitive layer is not sitting tight against the pcb.  This can be fixed by screw modding that area.  Or you could go ahead and bolt mod the whole thing. Unfortunately, broken rivets are the Achilles heel of these awesome boards. 

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Offline ThoughtArtist

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #4 on: Sat, 04 August 2018, 23:05:55 »
...when you realize the venerable Model M is more plasticy than a modern Cherry MX Brown TKL...
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Offline pixelpusher

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #5 on: Sat, 04 August 2018, 23:11:36 »
But the good thing is that bolt modding or screwing the sandwich layer back together will make it good as new for another 50+ years!
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Offline E TwentyNine

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #6 on: Sun, 05 August 2018, 07:53:38 »
This sounds like lost rivets.   Due to the location, you can skip a bolt mod for now and just do the following.

Open up the case, take the assembly out of it, make sure that is what's going on.  Then take a piece of paper, or a business card etc, fold it and put it in the bottom of the case under where those keys would be.  What you're trying to do is squeeze the metal backplate to the barrel plate.   Don't do too much as there's little tabs on the case that hold the assembly in that could snap.  Put the assembly in, add a little more paper til things seem snug, etc, try the keys without putting the case top back on.
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Offline Cheemio

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #7 on: Sun, 05 August 2018, 15:59:23 »
Quote from: pixelpusher on Sat, 04 August 2018, 22:20:56
Sounds to me like the plastic rivets in that area have all broken and now the capacitive layer is not sitting tight against the pcb.  This can be fixed by screw modding that area.  Or you could go ahead and bolt mod the whole thing. Unfortunately, broken rivets are the Achilles heel of these awesome boards.
I opened it up today and found all the plastic rivets are still intact. Unfortunately there is some rust on the barrel plate, right in the area where these problems are happening. I suspect this may be what is causing the issue. It doesn't look too too bad. Maybe some of the rivets in this area look a little suspicious as well?

Do you think a screw or bolt mod would still help in this situation? I was considering doing one anyway, as people say they improve the feel and longevity of the board.

Quote from: E TwentyNine on Sun, 05 August 2018, 07:53:38
This sounds like lost rivets.   Due to the location, you can skip a bolt mod for now and just do the following.

Open up the case, take the assembly out of it, make sure that is what's going on.  Then take a piece of paper, or a business card etc, fold it and put it in the bottom of the case under where those keys would be.  What you're trying to do is squeeze the metal backplate to the barrel plate.   Don't do too much as there's little tabs on the case that hold the assembly in that could snap.  Put the assembly in, add a little more paper til things seem snug, etc, try the keys without putting the case top back on.
That's an interesting idea! I may try this as a solution for the time being.
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Offline fohat.digs

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #8 on: Sun, 05 August 2018, 16:18:10 »
Those rivets look great and the rust looks like no big deal to me.

How many times have you tried re-seating the stems? And have you tried it while standing the keyboard up on its front edge so that the springs flop forward, and then standing on its back edge so that they flop backward?

The spring needs to be centered on a tiny dimple in the top (bottom when you have it in your hand) of the key stem, and it can take many tries. I would not give up until you have tried it multiple times, with the springs hanging/standing in different positions.

Otherwise, if the plates have separated, then the "ears" on the pivot plates could have fallen out of their slots and you will have to take it apart to fix it.
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"Starting in 2011, the deficits again started to shrink. During Obama’s term  the deficit was reduced by $900 Billion  before finally in 2015 the GOP managed to wrangle a “reconciliation” bill out of Obama where he again cut corporate taxes, as well as made permanent some of George W. Bush’s original tax cuts. This is the year everything reversed. Before this, under Clinton, Bush and Obama the deficit in almost every year was gradually decreasing. The balance we had of taxes and the economy was bringing the deficit down, the money coming in was slowly catching up with the money going out until 2015. Trump’s subsequent tax cut has continued the new trend even after the rest of Bush’s cuts have since expired. Obama had an average GDP of 2.3%, with 11.6 million jobs created and unemployment peaking at 10% in 2009, then falling to 4.3% in 2016. If we had continued on that downward deficit track, we would have again reached balance and another surplus in 2017-2018.
– Frank V Walton 2025-07-01

Offline Cheemio

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Re: IBM Model M - Key does not register unless fully depressed
« Reply #9 on: Sun, 05 August 2018, 22:26:23 »
I've now tried each switch around 10 times each. I have been using SwitchHitter to detect the keypresses and these few keys are the only ones that do it. What's odd about these springs is that they are super "stiff", they don't wobble around in different directions while you move the keyboard around. They just stay straight. I'm not sure if this is part of the issue though, as some keys that have this property DO work. If I have to take the keyboard apart to fix this, that's not a huge problem to me.

Also, another issue I discovered is that there's a crack in the corner of the internal plastic plate. Because it's there the left corner seems to wiggle a bit if you press on it, and if you press left control, you can literally see the whole left side of the board wiggle. Ooof. It's a shame because the case and keycaps are nearly flawless.
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