Unicomp Model M: PrintScreen key suddenty not working.

[Professor Fate]

Hello guys /* and girls, if any are present here */,

I've recently run into another strange issue with my Model M: The "Print Screen" key isn't working anymore! To exclude a software issue, I tested the board by using xev and xinput. No scancodes were emitted. I went one level deeper and did a USB traffic snif using Wireshark, and again: No reaction when typing the key!

The tactile feddback of the key seems normal. I removed the keycap and found the T-shaped hammer exactly in the position expected /* I could send you a photo if desired */.

So: What is going on now? Please don't say I'll have to do another screw mod!  Thank you.

[Tactile]

What does this tool show?

[Professor Fate]

I've only got a Linux box here, sorry!

[Professor Fate]

BTW, I tried out showkey --scancodes, which gives yout the exact scancode of a key. And: The key emits nothing.

[Kavik]

If the key still clicks, then it sounds like debris or liquid interference; however, it is weird that that is the only affected key if that's indeed the case.

You could open the case and unplug the membrane from the controller and plug it back in just in case one of the traces isn't making contact with the inside of the plug thingy.

Unfortunately, it's really hard to see membrane problems with Model Ms since you have to break them to access the membrane.

[rowdy]

Unplugging/plugging the membrane connector might solve it, and even cleaning it while it is unplugged.

But it sounds like this keyboard is screw-modded, so it's not quite as bad to disassemble it to check for membrane breakages.  Not quite.  Nearly.

Or try adjusting the tension of the screws around that area.  As counter-intuitive as it sounds, I have been recommended several times on good authority that loosening some screws can help, even in situation where you'd think that they need to be tightened.

[Professor Fate]

Well, the only thing I've found out so far is that the key, which lies right beneath the broken PrtSc key, does not click at all, but it works. I can remember that I adjusted the screws to make the key more clicky, but it didn't really work. The PrtSc key did wirk at that time, though, yet started to make trouble some 2 months ago.

I've also removed the cap of the broken key, but the rocker is apparently in place.

[Professor Fate]

OK, I've just removed and re-installed the PCB and then loosened two screws in the vicinity of the respective key. No use, the key remains dead. Here is a pic of the guts of the key (top) as well as of the Compose key, which works, but doesn't click (bottom): https://photos.app.goo.gl/Axpu8R65wgdWT7e49