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geekhack Community => Keyboards => Topic started by: jjlee88 on Tue, 02 February 2021, 09:20:17
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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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Strange indeed. Have you tried reflashing?
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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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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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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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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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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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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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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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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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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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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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Hey, thanks for the tips! Guess i'll figure something out. You've been really helpful.
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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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Who said anything about Enter, the sacrificial ISO key is next to left shift (https://cdn.geekhack.org/Smileys/solosmileys/laugh.gif)
Glad you got it working, thanks for the update.