Strange IBM F 122 Issue

[dontworriaboutit]

Hey all, been going through a doozy with this one.

I have an F122 from Sept85 that developed random keypresses being registered after a few months of continuous use. At first I thought that the foam was very likely in need of replacement. I used a neoprene sheet and did that, but my issue persists. I have done more investigating it the issue appears very strangely.

If I plug in the kb, at first it behaves pretty nicely. After some time, striking the keys with a decent force will register keypresses everywhere. Keys at opposite ends will register. At its worst, if I let the space rise too quickly, the keyboard will go bonkers, hold some keys down, type many all at once, lock my PC...

The issue is much worse and easy to make happen if the case is put on. If I tighten the case fully, the keyboard will almost be totally unusable pressing keys everywhere.

Pls Help

[XMIT]

Are you using the original controller or an xwhatsit?

It sounds like you've got a grounding issue somewhere. Something might not be seating right or there might be some gunk or grit hiding somewhere.

With an xwhatsit you could maybe change the threshold level but that's about it.

Good luck.

[fohat]

Are all the plates being held together with firm and uniform compression?

My experience with using foam that is somewhat thicker and more firm than the original is that you need to keep it all tight and together.

That is why I add 3 bolts: 1 in the center of CapsLock-Left Shift/Left F6-Left F8, a second between main 5 and upper F5, and 1 just right of ANSI Enter diagonally above left arrow. After doing all I can with the original tabs, tightening down these 3 can make a big difference. (Be sure to avoid the traces in the PCB when drilling your holes!)

[dontworriaboutit]

I am using the original controller with soarers.... But I did notice that my grouding cable/bolt was a bit loose. I took it a part and tightened this.

The plates were very difficult to put back together, I read about the bolt mod but I finally got mine together and it does seems to be pretty solid.

I'll keep an eye on it today, it doesn't seem to be doing anything weird atm, but this issue likes to hide until I've starting playing a game.

[just_add_coffee]

It sounds like you've got a grounding issue somewhere. Something might not be seating right or there might be some gunk or grit hiding somewhere.

I was putting an F AT back together last night, and it would go absolutely nuts spitting out random keys until I screwed the controller onto the base plate. The keyboard was fine after that.

Are those screws connecting the controller to the base plate how the keyboard is grounded?

[dontworriaboutit]

So it started having troubles again after that bolt was tightened down.

I got pretty upset, but this weekend I had time to take it all apart, clean and reassemble. I also really made sure this time that the plates were firmly in place. I put it back together and now it works beautifully. I can impact it where ever at it doesn't go berserk, if I let the keys really fly, still no troubles..... Yay!

I do notice that in the center rows of the keyboard the barrels are able to move slightly. I applied a bit of pressure in the suggested areas of the bolt mod and noticed that they don't move. It looks like bolt mod will be next project down the line.

[micrex22]

I've had this issue before: it's the ancient ribbon cable. Those ribbon cables are pretty stale at this point and can cause intermittent connectivity between the PCB and controller.

Sometimes it can be calmed down by bending around, else just replace it with IDE cabling.