1985 Model M printing phantom characters and odd behavior

[multicam]

Hello I am a lurker in the keyboard community. My main work is programming and I use equipment some would consider to be antiquated or obsolete. I do my work on old DOS and Windows machines and my keyboard is a 1985 Model M. After years of faithful service, the keyboard is experiencing some problems. First, every now and then the keyboard will spit out random nonsense characters like this:

@@)*&*(@&IJJHEYa8edyb9q2387e89*@&088#)&rn9r8w4#&*&N#KJkj

Or other times it will spit out lines of text saved to the clipboard. And it will just keep going and going. So I check the keyboard in the Switch Hitter app and it's showing the number pad "2" key being pressed like as a ghost. So I push that key and the random nonsense/clipboard characters stop. However an hour later the keyboard does it again, again with me pressing the number pad "2" key to stop the behavior, with the key showing being activated in Switch Hitter just prior.

My other problem is sometimes I will be pushing one of the keys in the QWERTY row and randomly the volume on my PC will go up and down. It's strange and I can't make heads or tails of it.

The keyboard has not been cleaned or modded and I estimate that it has about 50 intact plastic rivets on the internal assembly.

I use the Model M over PS/2 connected to my Windows 7 PC.

Thank you for any assistance or knowledge.

multicam (real name Jesús)

[Coeus]

I am not sure the two things you describe are necessarily related.

The number pad 2 key sounds like its own problem. With the IBM buckling sprint keyboards, of which the Model M is a type, when the key is not being pressed, a spring keeps the flipper off the PCB so no keypress is detected. When you hit the key, the spring buckles and the flipper contacts the PCB, resulting in the keypress being detected. Sometimes the spring can be in slightly the wrong place on the bottom of the keycap, come off the flipper, or have become damaged that can cause a key that is not visibly down to still be detected as pressed.

One thing you could try is reinstalling that key. The New Model F manual suggests doing that with the KB vertical and the spacebar uppermost. If that doesn't solve it, read through more troubleshooting things in there.

Random characters seems like more like an issue with the microcontroller, any converter and the communication between them. Check for bad connections, especially a continuous ground between the PC and KB.

[Falkenroth]

Interesting problems to say the least. This IBM keyboard will have a few sheets of membrane that the flapper will press down on. 1985 is the oldest version of the Model M so it might be time for a tear down and inspection of the springs, flappers, membranes and so on. Specially if it's a daily use keyboard. I own a few 1985 boards but I don't daily them. No screw or bolt mods on them yet. My daily use board is a Jan 1987 1390131 but it has had a recent screw mod and inspection. Still can't rule out other things like the controller or adapter. The 1985 controller is super rare and has 4.00mhz crystal on it.

[Falkenroth]

This link on Geekhack describes some common issues. https://geekhack.org/index.php?topic=88397.0

They talk about it being a rare controller.