IBM Model M - Actuation before Click.

[norc]

Howdy.

I have an IBM Model M 1391403, several of my keys actuate (register the key press) long before the click.

While most of the time it's not a problem, but since I just cleaned out my keyboard, a few of these keys now register by merely resting my finger ontop of it (meaning pushing it down with the mere weight of my finger causes actuation).

Now it is still usable, but annoying nevertheless.

Any tips other than "Buy a new one" ?

[fohat.digs]

Hard to imagine how that could happen.

The entire concept of the switch is that it is the "catastrophic buckling" of the spring that strikes down on the hammer (aka foot) of the assembly.

The first step is always to pull the key stem, jiggle the spring a bit, and reset it. Sometimes it takes several tries. And maybe stand the board upright (on the front (spacebar) edge) to get the springs centered and leaning down.

No key at all keeps the switch in the "open" position, so maybe yours is almost off.

[norc]

Yeah indeed it is hard to imagine.. though I somehow got used to some actuation a tad bit before the click, but that's not really an issue.

I tried resetting it so many times, it just does not change anything.

Can you elaborate what you mean by "No key at all keeps the switch in the "open" position, so maybe yours is almost off." ?

[fohat.digs]

That was probably a poorly articulated observation.

Pull the "F" key and you will get an endless string of "Fs" until you put the stem back in. (At least that happens on the Model F, I have not used a Model M regularly in a year or so.)

[urbanus]

but since I just cleaned out my keyboard,

Exactly what did you do when you cleaned it?

Guesses:
* Misaligned hammers.  Shine a light down the barrels of the affected keys, see if the hammers have shifted.  This can be fixed with a pair of needle-nose pliers.  Gently pull the hammers back into place.
* Fluid contamination of the membrane.  You could try leaving it in a warm, dry place for a few days and see if the problem rectifies itself.

[rootwyrm]

but since I just cleaned out my keyboard,

Exactly what did you do when you cleaned it?

Guesses:
* Misaligned hammers.  Shine a light down the barrels of the affected keys, see if the hammers have shifted.  This can be fixed with a pair of needle-nose pliers.  Gently pull the hammers back into place.
* Fluid contamination of the membrane.  You could try leaving it in a warm, dry place for a few days and see if the problem rectifies itself.

Ding, that, exactly. Either that or a badly done bolt mod where it's overtight or hammer retention's otherwise been substantially compromised. Indication is that the hammers are on membrane at rest. So it's not keycap installation. It's hammer or membrane.

[norc]

I merely pulled the keycaps off, dusted it out with some canned air (carefully enough to not cause condensation), and put it back together - that was it pretty much.

Now I looked inside the key barrels, they all look the same. However, I found hammers that seem totally lose - jiggling between both position. Is that normal? Or is the buckling spring supposed to pull them away from actuation until buckled?

[Magnusian]

With the stems removed nothing really holds the hammers in place though the lack of anything pressing them down should not actually cause a keypress to register. When you've been re-seating the keys have you been lifting the front of the keyboard so that the spring rests on the back of the barrel before inserting the keys? If not, there's a chance the spring doesn't seat properly in the stem which can definitely cause issues.

[norc]

It's starting to sound more like a membrane issue. Is it possible to open up the keyboard and expose the membrane (without damaging anything) to see what's going on there?

[Magnusian]

It's very easy to take it apart without damaging it. Putting it back together after, now that's the trick.

[rootwyrm]

It's very easy to take it apart without damaging it. Putting it back together after, now that's the trick.

It's not the membrane. It's the hammer retention mechanism. (I don't know of a better way to describe it.)
With keycaps removed, the hammer should have NO play and be up. That means if you gently grasp the spring and pull upward very gently, there should be no movement. I wish I had some pictures to show it, but I haven't had to pop apart to that extent in ages. The default position of the hammer is always OFF (up) with keycap removed and there is no linkage between keycap and spring. It's an entirely floating assembly.
From what it sounds like here, your hammers are in fact resting on the membrane, which means essentially broken. It's impossible to determine whether it's the mounting plate (plastic assembly on top) or the hammers themselves without disassembly.