Problem with IBM Model F 122 key

[EDI]

So I have been using the Model F 122 key keyboard for a while now, but today I ran into some serious problems with it. The keyboard basically started registering all keys randomly. It would for example just start hitting F9 or 6 key continually. Or register multiple keys when I only pressed one key.

Has someone had this kind of problem before? Where do you suspect the problem is? Is it PCB or controller related or something else?

[fohat.digs]

I have had similar things happen because of what turned out to be plate pressure problems.

All of my F-122s have been ANSI modded and disassembled, at the minimum, and usually with new mats cut and a few bolts added.

Generally, when I have faced a situation like yours, I have been able to loosen or tighten my bolts, with or without breaking down and separating the plates, and gotten it fixed. Most of the time, tightening the bolts was the ticket, but the last time I needed to loosen them. I had cut a thinner than usual mat out of a softer material, so perhaps it wanted a little more space.

If yours is a virgin, it may be that the foam mat has completely broken down and needs to be replaced.

[Melvang]

I concur with fohat.digs, though I have yet to add bolts to mine, but then I don't have any of the taller boards, just a couple XTs and an AT.  Those don't have any issues with plate tension.  I would recommend a mat replacement though.

[vivalarevolución]

I concur with fohat.digs, though I have yet to add bolts to mine, but then I don't have any of the taller boards, just a couple XTs and an AT.  Those don't have any issues with plate tension.  I would recommend a mat replacement though.

And hire Melvang to do the mat replacement for you!

[EDI]

What mat I should get for replacement?

[fohat.digs]

I like art foam which is available in sheets of approx 1' x 2' x 1/16" from Michael's Art Supply for $1

Others like 1.5mm soft neoprene from McMaster-Carr

There is also very thin very soft packing plastic foam.

In whatever case, you will need a 5/8" hole punch or do the work with a sharp Xacto knife.

I discuss it in my "Harry's ANSI mod" for F-122.

https://geekhack.org/index.php?topic=48786.msg1048948#msg1048948

[Melvang]

I could just make you a new mat?  I have a plate on hand, and can make one and put it in the mail.  $20 plus shipping.

[EDI]

Okay I checked the mat and it was most likely replaced by a previous user. It consisted of two separate foam parts. One for numpad and nav cluster area and other for rest of the board. Do you guys still think the problem is with the foam?
The board is now somehow working flawlessly, but the problem may come back.

Here are some close up pictures of the side of the foam:



Seems to be right thickness?

[Bucake]

foam on my 122 fills up the space between upper and bottom plates, it's probably three times as thick.
not sure if that matters when it comes to the keyboard working properly or not, though.

[fohat.digs]

The plates have to be the "right" distance apart - not too close and not too far.

The reason I started adding 2-3 bolts near the center of curvature longitudinally is because I felt that the curved plates had a tendency to spring too far apart after being disassembled and "messed with" often including a thicker and/or firmer mat.

[EDI]

The problem suddenly came back yesterday. There really seems to be no rational explanation for it.
Anyways I noticed that when the problem occurred, the orange led in Teensy started blinking. Does anyone have an idea what that means?

[1391406]

If it were me, I'd try disconnecting and reconnecting the USB. Failing that, I'd reboot the PC.

[fohat.digs]

On the rare occasion when I have experienced something like this, a minor tuning of tightening or loosening my center screws has taken care of it. I think that you are seeing a plate spacing/compression problem that is altering capacitance.

[EDI]

On the rare occasion when I have experienced something like this, a minor tuning of tightening or loosening my center screws has taken care of it. I think that you are seeing a plate spacing/compression problem that is altering capacitance.

Okay so only solution would be to do a bolt mod? Could the thin mat on this keyboard cause this?

[fohat.digs]

Okay so only solution would be to do a bolt mod? Could the thin mat on this keyboard cause this?

Don't rush into anything. I am a "tinkerer" and have been generally successful with my trials and errors, but I can't make any guarantees.

Also, it is hard to see, but I would call that mat rather thick, not thin. Chances are greater that the plate assembly has too much space rather than too little. I like to manage the sound of keyboards, so I prefer a denser foam of 1/16"=1.5mm cranked down snug for tighter feel and attenuated sound, but many people use thinner and/or softer foams which also have the benefit of making the re-assembly much easier.

My first suggestion would be to press on the plates from the back (inside to the curvature) and the stronger your hands are, the better.

Then try taking it apart and putting it back together, forcing all the pieces into each other as tight as you can.