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Author Topic: Unwanted key trigger when pressing key combinations  (Read 1854 times)

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Offline jjlee88

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Unwanted key trigger when pressing key combinations
« on: Tue, 02 February 2021, 09:20:17 »
The PCB in question is a KBD67 Rev 2. As seen in the video, the ESC key gets triggered when the following combination of keys are pressed: Tab + W + 3. Has anyone encountered such issue before? Testing the individual keys are fine and yielded no issues whatsoever.
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Offline diazel

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Re: Unwanted key trigger when pressing key combinations
« Reply #1 on: Tue, 02 February 2021, 13:08:50 »
Strange indeed. Have you tried reflashing?
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #2 on: Tue, 02 February 2021, 18:45:47 »
It is! I've tried flashing different firmware, the default one, the VIA one, you name it. They all have the same issue. I would like to say that it is a hardware issue, but the individual key tests all looked fine.
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #3 on: Tue, 02 February 2021, 18:56:37 »
Sounds like a ghosting issue which shouldn't happen with diodes, maybe a diode attached to one of those keys is soldered backwards?
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #4 on: Tue, 02 February 2021, 19:52:58 »
Without knowing too much about the intricate details of a keyboard PCB, that seems like a plausible explanation. However, this  doesn't happen when Tab+3 is pressed. It happens when specifically Tab+W+3 is pressed.
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #5 on: Tue, 02 February 2021, 20:16:56 »
It is strange but they are possibly 3 corners of a square so the current that's supposed to go from the top row down the column to register as a 3 could go down to W, across to Tab then down to register the end column which would be Esc.  Does it do anything strange with 3 W and U or Tab 4 and R?

If you have a continuity tester the diodes should only beep with the probles one way, not if you swap them.
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #6 on: Tue, 02 February 2021, 23:11:48 »
Very interesting indeed! Tab+4+R didn't show any issue, but 3+W+U triggered 8! So what's the theory?
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #7 on: Wed, 03 February 2021, 13:08:08 »
Thinking about this it can't be a backwards diode or each key wouldn't work alone so you you definitely have a dead one.  To work out where I guess you need to try another row - 3 S and Caps lock would make 3 broken?  I'll think about this and have a look at the PCB or firmware when I get home later.
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #8 on: Wed, 03 February 2021, 19:03:09 »
Thank you for looking into this. Yeah it makes sense that a diode soldered backwards would have broken that key, but the key tests are fine. Caps+S+3 didn't show any issue.

New information though, when holding W+3, pressing anything in R3 will result in the corresponding R4 triggered. E.g. W+3+E results in 4 being triggered, W+3+R results in 5 being triggered, etc. So it is indeed a ghosting issue and I guess we can narrow the problem down to W+3?
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #9 on: Wed, 03 February 2021, 19:55:43 »
No problem, I like working these out.  Except it's black so I can't see anything :mad:  At least the firmware reveals it is a sane matrix and where the gaps are.

I'm still struggling to get my head round this for some reason but as S and 3 didn't break it I think the problem diode must be the one on W.  If so Tab W and S should press Caps, Tab W and X should press Shift, and Tab W and Alt should press Control?  I'm assuming you have all the keys mapped as standard ANSI/ISO.
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #10 on: Wed, 03 February 2021, 20:06:53 »
Yeap, you are right, the key combinations you mentioned triggered the issues as you've suspected. So it's a problem with the W key.

Yes, the keys are all mapped as standard ANSI.
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #11 on: Wed, 03 February 2021, 20:28:04 »
Well that's solved then - you just need to replace the diode on W and all will be well.

If you're comfortable with SMD soldering there is a diode on the switch next to left shift you can use (if you're never going to use ISO), same for split spacebars, split backspace or if you use 2x 1.25 mods on the right instead of lots of 1u keys...  I would give you numbers but it's black and I can't see what's connected to what.

If you're not confident with SMD soldering you can cut the trace between W and it's diode then solder a through hole diode between the switch pin and the far side of the broken diode and it will work just as well.  If you need help with that post a picture with the traces around W highlighted in the shine from a light and I'll scribble on it :)
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #12 on: Wed, 03 February 2021, 20:43:49 »
Hey, thanks for the tips! Guess i'll figure something out. You've been really helpful.
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Offline jjlee88

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Re: Unwanted key trigger when pressing key combinations
« Reply #13 on: Sat, 06 February 2021, 05:01:40 »
Hey, just wanted to update this thread saying that I've managed to fix the issue. It is indeed an issue with the diode on W. I tested it with a multimeter and there was low resistance across forward and reverse-bias.

I couldn't use the diode on the ISO Enter as replacement as it shares the same diode as the ANSI Enter key. I ended up using the diode on the split spacebar key. Thank you again for your guidance!
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Offline suicidal_orange

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Re: Unwanted key trigger when pressing key combinations
« Reply #14 on: Sat, 06 February 2021, 05:13:57 »
Who said anything about Enter, the sacrificial ISO key is next to left shift

Glad you got it working, thanks for the update.
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