Need help with PCB issue after Desoldering a Keychron k6 (Probably a Short Circuit)

So I’m desoldering a keychron K6 for a friend of mine (to millmax),

Just for context, I’m not that new to desoldering, I have desoldered about 300 switches at this point but I’ve never encountered any problems thus far, this is the first time I’m experiencing a real issue with the board.

So, as I was desoldering the switches, about halfway through I decided to check if all was good, and everything was working fine. But when I did end up finishing the switches and tested the board, when I tested one pad, it would register all the pads of the entire row at the same time or randomly. I’m guessing its a short somewhere on the PCB, note this is my first time dealing with this kind of issue, is there anything I should be looking out for, or if you could spot a problem through the images I will be sending please do point it out for me as I am unfamiliar with these kinds of issues.

Additionally, the desoldering job isn’t the best but I tested every pad and it still works so I’m pretty sure I didn’t lift a pad. I read a little online saying it might be a broken diode (?) however not sure what the actual problem is.

Any help / suggestions would be very appreciated!

testing the pcb after desoldering video

https:// imgur .com/a/arnLRG6

Close ups and more photos in the link!

Could you tell us what keys have this problem ?
As said before we’d need close-up photos around the switches that have a problem to check for traces issues.

Another thing, did you carefully inspected the MCU pins?
It is not uncommon to have dirt stuck between pins that makes electrical contact. It happened to me recently, and the process of desoldering is quite messy.

Hi thanks so much for the reply!

Actually, there are no “specific keys” that cause that problem, the problem is: anytime I contact any of the pads / activate any of the keys, the whole row activates all at the same time or in random intervals.

Will try to take some super close up shots in a bit!

Will also check to see if there is dirt around the MCU!

I added some photos to this post!
https: //imgur. com/a/arnLRG6

There are some spaces in your link, and by removing them we could not access it.

EDIT: works nows without the spaces.

I had to do that sinc keebtalk wont allow me to post links since I just recently made my account :confused:

From the images I see nothing obviously wrong, but with black PCBs is it always very difficult to tell.

Looks like the row/column scanning system is totally broken.
This is a very strange behaviour!
And I strongly doubt you did a mess on all key switches to have this result, your desoldering job looks nice BTW.

So I’d say to look carefully if something is not stuck between the MCU pins.
Look for dirt, solder ball, or solder bits that could have been stuck in between those.
The use of a magnifying glass is a plus.
And having a multimeter to check resistance between the pins is the best method than doing that visually.

Then, if nothing conclusive, maybe the firmware took a hit and need to be reflashed.
It looks to be possible on the Keychron K6, info here:

Now I don’t know if doing that will ruin you PCB definitely or not, dunno own a keychron and never tested myself, so it is at your own risk.


Alright update: Thanks so much for the tip btw!

I managed to reflash the board without bricking it but the problem still persists, I’m guessing it really is some dirt, I’ve cleaned the PCB multiple times with IPA. Still cant seem to find where the problem is at.

Final update: Finally found out what was wrong:

To anyone who encounters this problem it seems like use raw tweezers on the PCB doesn’t seem to activate it properly. I tested this theory out by soldering on some millmax sockets and activated the pcb using an actual switch, and it seems to work fine for now, if you’re curious please see the link.

https:// imgur. com/a/rpjhVRx (just remove spaces in the link)



Never saw that kind of pb before !

Thanks for the info :slight_smile:

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So, are the tweezers passing more current than the resistors can handle? Something like this, right? Very curious, but also really smart move to try a switch. Glad you solved it.