Some key combinations cannot be pressed

DAMO238 · 2020-04-02 15:18:04

Most of my keys work perfectly with each other. This may be a hardware issue as my backtick key kept pressing itself, so I used xmodmap to disable it on starting xorg. The keys do not even appear in xkeycaps when I press them and it is only the first key that shows up. Examples:

Right Shift+Z => Right Shift
S+A => S
A+S => A

There are other keys that do this, but this is just to show what I mean. Every key individually works perfectly (bar the one I disabled of course) and I couldn't find anything useful about this issue in the wiki unfortunately.

Trilby · 2020-04-02 15:26:58

DAMO238 wrote:

This may be a hardware issue as my backtick key kept pressing itself

As it you'd keep getting a stream of backticks? If so, that would be sufficient to create the symptoms you describe.

For example, on my thinkpad, I just tried holding down the 'a' and then hitting 's'. I had a terminal open, so while I held down 'a' I was getting a stream of 'a's on the screen until I hit the 's', at which point the 'a's stopped and an 's' was printed. If I then kept the 's' held (so 'a' and 's' are both pressed) I'd get a string of 's' which could be similarly interupted by other keypresses ... but not by a backtick.

Similarly, if I held down the backtick first, then 'a', then hit 's' the 's' was never registered. Also if I held the 'a' and then pressed and held the backtick followed by the 's' the 's' would not be registered. The same with `sa and s`a.

So, on my keyboard at least, a third key is registered while two other keys are held, but not when the three keys include the 's', 'a', and backtick (in any order) - in these cases, the third key does not register.

If your keyboard is similar, and there is a steady stream of backticks, you would get the results you describe - X may ignore the backticks, but they are still being sent.

EDIT: though I have no such problem with backtick, rightshift, and 'z' all pressed.

EDIT 2: I get the failure of third key when 'a' and backtick is held and the third key is any of the home-position keys (asdfjkl;) but not when it is any other letter key including g+h which are in the middle of that row on my qwerty keyboard. Holding a and backtick also prevents number keys 5 and 6 but no other numbers. Oddly, this is asymetic, as holding back and most of these home-position keys does not prevent the 'a' from registering unless it's backtick+s that does prevent the 'a' from registering. I've found a few other combinations that prevent the third key, but no pattern is emerging.

Last edited by Trilby (2020-04-02 15:33:57)

DAMO238 · 2020-04-02 15:48:29

Dang, I was hoping that wasn't the issue. Seems like all hope is lost for fixing that then. While my symptoms are slightly different, this is probably the same issue just with slightly different hardware. I also get the lack of 5,6 and the left side of the home row bar g and h, which also suggests its the backtick stream issue. Thanks for your help anyway!

Trilby · 2020-04-02 17:11:40

If it we're me, I'd break the backtick key more. You can't use it as it is anyways, so I'd open up the keyboard and cut any contact limited to the backtick key: prevent it from registering even in the hardware.

ewaller · 2020-04-02 17:57:12

Trilby wrote:

If it we're me, I'd break the backtick key more. You can't use it as it is anyways, so I'd open up the keyboard and cut any contact limited to the backtick key: prevent it from registering even in the hardware.

DAMO238 · 2020-04-03 15:21:38

Yeah, I was thinking about that, but I'm a bit wary as it is a laptop, and I don't want to accidentally break anything else during disassembly. Thanks for the suggestion though!

Trilby · 2020-04-03 16:04:12

It's very easy to remove the keyboard from most laptops with minimal dissasembly. Many of them even have replacement keyboards available on ebay for pretty darn cheep (or sometimes just as-is models for cheep, but with good keyboards).

Although I say this as a lifelong thinkpad user. Thinkpads are a bit easier than average to dis/re-assemble. Most other laptops though are still not much hassle. Except macbooks. Never open up a macbook if you value your sanity.

Arch Linux

#1 2020-04-02 15:18:04

Some key combinations cannot be pressed

#2 2020-04-02 15:26:58

Re: Some key combinations cannot be pressed

#3 2020-04-02 15:48:29

Re: Some key combinations cannot be pressed

#4 2020-04-02 17:11:40

Re: Some key combinations cannot be pressed

#5 2020-04-02 17:57:12

Re: Some key combinations cannot be pressed

#6 2020-04-03 15:21:38

Re: Some key combinations cannot be pressed

#7 2020-04-03 16:04:12

Re: Some key combinations cannot be pressed

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