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Fixing Double Inputs and flickering LEDs? (imgur.com)

submitted 3 months ago by [email protected] to c/[email protected]

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Hello fabulous fellow keeb enthusiasts! I have this really cool custom split ergo keyboard called a Dark Matter, and I think only 10 or so were made. I love typing on it, but I'm getting double inputs and the LEDs on the left side only work intermittently. Do you have any suggestions on how I could try to fix those issues? Do you think I need to resolder both PCBs entirely, just certain key switches, and/or all the LEDs? Reseating its teensy controllers did not fix the issue, for example.

Unfortunately the person who made these is not providing support for them so I'm on my own on this one.

Here's a reddit post I made 5 years ago when I first ran into these issues:

https://old.reddit.com/r/AtomComputer/comments/9rc2ep/leds_and_doubleiinputting/

I'd appreciate any advice you can offer, thanks so much!

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[–] [email protected] 2 points 3 months ago (1 children)

It's hard to tell if it's a similar cause, but I had issues with double-inputs and occasionally keys would work intermittently on my Dactyl Manuform.

After getting frustrated enough having resoldered it several times, I hot-glued the PCBs to the case. The thinking that small movements during a key press was causing the contacts to be broken. Everything has been working great ever since!

If you want to be cautious and have a multimeter, you could also check the connections between the keys. That might help isolate where to focus your efforts.

[–] [email protected] 2 points 3 months ago* (last edited 3 months ago)

Will do, thanks so much! And good tip about the Glue! I have noticed on the left half (which is the side with the intermittent LED issue), that if I flex the assembly a smidge I can get the LEDs to come on, so it probably is a bad solder joint somewhere or something

[–] [email protected] 2 points 3 months ago (1 children)

Kind of difficult to give recommendations on where to start for resoldering, but my first hunch would be cold solder joints somewhere. I have a Kyria from splitkb that I assembled myself that had spotty LEDs on one half which turned out to be a cold joint on one of the surface mount underglow LEDs. Also had no key presses registered on a row that turned out to be a cold joint at the MCU.

As for general troubleshooting recommendations, if you can get a board schematic that would be immensely beneficial for your efforts as it would show how and to what pins of your MCU everything is connected. With that you can try to identify where the fault might be occurring (e.g. LEDs die after LED 5 in the chain) and focus your efforts before/after that area.

Failing the board schematic, you may be able to just visually see where the traces connect back to on the PCB, or you could probe it out using continuity mode on a multimeter and reverse engineer the connections.

Another thing that may aid in diagnosing where the issue lies with the double key presses is figuring out how the key matrix is laid out. For example if you're receiving double presses on only some keys in a single row or column, the issue lies in either that row/column or the MCU pin they connect back to. Again, the board schematic would be really helpful in this regard.

Best of luck!

[–] [email protected] 2 points 3 months ago

Great advice, thanks so much! I don't think I'll be able to source a board schematic because I believe it was a one-off small run, but I can follow the traces on the PCB. My friend is an electrical engineer and he and I will test with his multimeter and see what we can figure out! Thanks again!