Keys not working

[ronnieb555]

Hi everyone, this is my first keyboard mod/solder.

My keyboard is a Keychron K2V2 UK-ISO and my plan was to de-solder all the switches to lube/film them and also fix the stabs. Unfortunately after doing that, when it came to soldering the switches back into the keyboard the soldering iron's tips that I purchased started to melt and looks to have caused damage to some of the contact points on the PCB.

From my testing so far the M key and also every key on the second row down (Numbers, backspace, etc...) all do not work. The contact points on the M and backspace key look "burnt" to me so I think that's why it isn't working but I am no expert so I'm hoping for someone's advice to see if this keyboard can be saved?

Fortunately the company that sold me the soldering iron have admitted fault and compensated me, but ideally I would still like to save the keyboard.

I've attached images of the PCB and the two contacts that look "burnt" to me. Also there are 3 empty switch locations as with the iron melting I stopped soldering and wasn't able to solder in those switches.

Does anyone have any advice on what to do or if this can be saved?

[ronnieb555]

Just for a laugh I thought I'd include pictures of the melted tips

[MajorKoos]

YOLO it and finish soldering it up.
As long as you haven’t lifted pads off the pcb or melted the switches you should be fine.

[ronnieb555]

YOLO it and finish soldering it up.
As long as you haven’t lifted pads off the pcb or melted the switches you should be fine.

Could it not damage the board further though if it continues to melt?

I think I'll order some replacement tips that are higher quality and solder in the last couple of switches, but when I use a set of tweezers on the contact points of those, they are fully working.

[suicidal_orange]

If you lose the odd switch usually you can just solder jumpers to the diode or another nearby switch to fix it (like your lower/right pin of M can be connected to the lower/right pin of N) but if you're unlucky and your board was badly designed (read: nearly every off the shelf keyboard) you can kill the pad where the whole row links back to the controller chip, which is not so easy to fix.  It looks like the controller chip on this board is under the space bar on the left side so it is very unlikely that the row links to it from backspace.

By coincidence I helped someone with another Keychron recently and theirs wasn't the stupid matte black that looks great unless you're trying to see the connections, it was helpfully green!  Based on what I can see on their pic I think the link is in the blue circle(ish), specifically I think there's a small hole (a via) under the 2 in the ND20 label.



Can you see a hole there attached to a trace going down between the diode (ND20) pads?

[ronnieb555]

If you lose the odd switch usually you can just solder jumpers to the diode or another nearby switch to fix it (like your lower/right pin of M can be connected to the lower/right pin of N) but if you're unlucky and your board was badly designed (read: nearly every off the shelf keyboard) you can kill the pad where the whole row links back to the controller chip, which is not so easy to fix.  It looks like the controller chip on this board is under the space bar on the left side so it is very unlikely that the row links to it from backspace.

By coincidence I helped someone with another Keychron recently and theirs wasn't the stupid matte black that looks great unless you're trying to see the connections, it was helpfully green!  Based on what I can see on their pic I think the link is in the blue circle(ish), specifically I think there's a small hole (a via) under the 2 in the ND20 label.

(Attachment Link)

Can you see a hole there attached to a trace going down between the diode (ND20) pads?

Thanks a lot for the info, yes there is a small hole under the 2 in the ND20 and I can see lots of traces going down to the chip with the purple paint on it.

Here are some better pictures to try show you the traces and the holes.

When you say "solder jumpers" do you mean solder wires from one pin to another? Sorry for the stupid question, just I'm not familiar with pcb's and electronic internals.

[suicidal_orange]

Great pics there - how did you get so much shine?!

Yes, jumpers (also known as bridges) are just wires, so to fix M just solder a wire to N like the green line.  I think backspace is damaged on the same pin so that would go to = if it doesn't work when the rest of the row is fixed.

Find something pointy to stick in the end of a bit of wire (a sewing needle?) and short the red dot to the second pin down on the side of the chip at the end of the cyan line with the keyboard plugged in and it should type ... whatever letter that key is.  This appears to be between the other row pins so you don't have to be too careful (it will just type the character above or below), this may sound risky but it's what the switches do when you press them.  If it does type the right letter you will need to carefully scrape the black mask off the trace and solder a jumper between either of the orange dots and the exposed area.  I suggest you scrape the blue bit where there are no other traces nearby, then solder the orange end and bend the wire so it sits right before soldering the other end.  Some hot glue to hold the wire near the trace end would be good too just so it doesn't get pulled up.

[ronnieb555]

Great pics there - how did you get so much shine?!

Yes, jumpers (also known as bridges) are just wires, so to fix M just solder a wire to N like the green line.  I think backspace is damaged on the same pin so that would go to = if it doesn't work when the rest of the row is fixed.

Find something pointy to stick in the end of a bit of wire (a sewing needle?) and short the red dot to the second pin down on the side of the chip at the end of the cyan line with the keyboard plugged in and it should type ... whatever letter that key is.  This appears to be between the other row pins so you don't have to be too careful (it will just type the character above or below), this may sound risky but it's what the switches do when you press them.  If it does type the right letter you will need to carefully scrape the black mask off the trace and solder a jumper between either of the orange dots and the exposed area.  I suggest you scrape the blue bit where there are no other traces nearby, then solder the orange end and bend the wire so it sits right before soldering the other end.  Some hot glue to hold the wire near the trace end would be good too just so it doesn't get pulled up.

(Attachment Link)

Thanks for all the advice, I've got some new soldering tips on the way to finish soldering the last couple of switches and then I'll try these jumpers.

I'll report back once I've tried it all out.

[ronnieb555]

So after getting my new soldering tips, I soldered in the last three switches that were missing.

Now rather than no key working on the numbers + backspace row, they all are "pressing" at the same time. I opened up a keyboard tester app and it just repeats numbers without me touching anything.

Is this still saveable or does that mean the board is dead? I do have some wire coming today so I will fix the M key and I'm open to try any other fix for the number row

[suicidal_orange]

Sounds like a Keychron!  Let me guess - some LEDs are doing something strange too?

I have never fixed a Keychron with LEDs because people always start asking when their board is as yours is now where the obvious answer would be a short which no-one can find.  So if you don't mind being a guinea pig please continue as above - either that connection is not broken and nothing will change or it is broken and this fixes it, and the mysterious Keychron design will have been solved.

[ronnieb555]

Sounds like a Keychron!  Let me guess - some LEDs are doing something strange too?

I have never fixed a Keychron with LEDs because people always start asking when their board is as yours is now where the obvious answer would be a short which no-one can find.  So if you don't mind being a guinea pig please continue as above - either that connection is not broken and nothing will change or it is broken and this fixes it, and the mysterious Keychron design will have been solved.

Thanks for all of the help with this problem, I just soldered two wires between the M and N and then also one between the backspace and the = and it's fixed all the problems.
When the keys were all pressing randomly, there wasn't actually a problem with the LED's they were flashing normally.

The full backspace row now works and there are no random keys being pressed.

Here is a picture of what I did, maybe it can help someone else in the future.

[suicidal_orange]

Thanks for the update and glad to hear it works, that's the main thing.  The mystery of Keychron's design remains, especially as your LEDs didn't do anything strange.