geekhack Projects => Making Stuff Together! => Topic started by: Fredigar on Sat, 09 January 2021, 11:17:09

Title: Keyboard PCB troubleshoot and repair (HELP!) Keychron K6
Post by: Fredigar on Sat, 09 January 2021, 11:17:09

I am very new to this forum and I apologize if this is the wrong place to post this topic. This is the one that made the most sense to me.

I recently bought my very first mechanical keyboard after doing a lot of research. I chose the Keychron K6 65% keyboard ( I bought the version with soldered key switches (accidentally, I actually wanted hot-swappable). I used the keyboard for about a week after which I started doing the mods I planned with my roommate.

I de-soldered the key-switches with a soldering iron and de-soldering pump (my roommate and I managed to break two which I have ordered replacements for). I then lubricated all the switches. I then put the switches back in the PCB (except the two that broke) and soldered them.

I plugged my keyboard in, and wow, it is not working correctly! I will now note all bits of information on its condition and its behavior:

1. The keyboard receives power when it is plugged in.
2. It didn't do a very careful job of making sure the key switches bottomed out on the PCB
3. The lighting key in the top right corner and the tab key do not have switches. Their sockets are covered with masking tape.
4. None of the switches are bridged in the open position when tested with a multimeter
5. All the switches close when in the closed position.

Note: I describe the lighting issues, but lighting is not a concern of mine. I have ordered blank keycaps.

Behavior doesn't change whether the battery is plugged into the PCB or not.

1. The escape key appears to change the lighting mode.
2. The lighting mode appears to change sporadically
3. A couple of columns do not light with the rest of the keys: 3, 4, 5, 8, and 10
4. In column 3, pressing ["S"], [X], or [Left Alt] causes all column 3 LEDs to light up. In column 4, all switches will cause the column to light up. In columns 5, 8, and 10, no keys will light.
5. (Using
*Columns and rows listed from top left to bottom right

*All keys not listed have no behavior

[ESC], [1], [2], [5], [Q], [T], [Y], ["U"], [Home]: cause all row 2 keys to stick

[A], [G] activates (only while depressed) itself and all row 4 keys.

["S"] activates all row 3 and row 4 keys.

[D] activates all row 3 and row 4 keys, will sometimes get stuck for a bit, and then cease.

[N] sticks all row 4 keys, will start after switch is barely pressed (like literally just putting your finger on it) and then stop after some time (this baffles me because the switch only closes half way down when tested with a multimeter). This behavior repeated itself accross ten trials. ** I just tested it again, and it will activate EVEN IF YOU AREN'T TOUCHING IT! If you hover your hand over the keyboard without touching it, IT WILL ACTIVATE.

[L ALT] activates all row 5 keys.

[Space] activates all row 4 keys and [WIN] key.

[Enter], [Page Up], [WIN], [R CTRL], [<], [v], [>] work as expected.

[FN1] and [FN2] appear to be working as expected

[FN1]+[ESC] activates function row

[FN2]+[1] activates [~], [F4, [F6], [F7], [F9], [F10], and [F11].

[FN2]+[2] activates [~], [F10], [Shift], and [Page Down]

So I'm not sure what exactly is the matter. But I would be very grateful if you guys could take a crack at some of these questions:

1. Does this seem like it could be an issue with the connections or with the keyboard controller itself?
2. Is the damage possibly reversible?
3. Is it possible for a professional electrical engineer to fix my board?
4. Would it be worthwhile for me to de-solder the switches to see what is on the other side?
5. Does it matter if two sockets are missing key-switches?

Thank you guys so much! And if you think I should post on another/a different forum, please let me know!
Title: Re: Keyboard PCB troubleshoot and repair (HELP!) Keychron K6
Post by: suicidal_orange on Sat, 09 January 2021, 12:58:12
First congratulations - this is indeed the place you should post when you have an issue that involved a soldering iron.  Not many people get that right :thumb:

I don't know how you managed to break switches desoldering them but it suggests your technique wasn't great.  That probably means you damaged some pads/traces which on most boards isn't a big problem but this is a Keychron and somehow the LEDs are linked to the switches, I've been trying to help with a less damaged one here ( but the PCB is black making it a nightmare to work out what's going on - I guess yours is black too?  A pic will give us a better idea of your soldering skill and how damaged the pads look anyway so please post one.

To try and answer your questions:
1 - I suspect it's just connections, but if you did manage to shock the controller chip that wont help
2 - Should be - hopefully when all the switches are connected properly it somehow magically works.  Note how you have problems in columns: 1QA, 5TG and whole rows which are usually due to a short
3 - Probably
4 - That would be useful if you know what you're looking at or the PCB is not black so you can take pics for others to look at.  A multimeter or continuity tester would be useful too
5 - No - all a switch does is connect the two pads when pressed.  If there's no switch soldered in they can't be connected so will do nothing

Random thought - can you turn the lighting off with the keys that work?  Maybe that will stop the power that's registering as extra keypresses (not a fix but more info is never a bad thing)
Title: Re: Keyboard PCB troubleshoot and repair (HELP!) Keychron K6
Post by: Fredigar on Sun, 10 January 2021, 11:04:22
@suicidal_orange thanks so much for the quick response. I will get you those pictures as soon as I can.

P.S. What do you make of [N] activating when I put my finger close to it? (My roommate does electronics as a hobby, and he corroborated)
Title: Re: Keyboard PCB troubleshoot and repair (HELP!) Keychron K6
Post by: suicidal_orange on Mon, 11 January 2021, 15:10:01
N is technically impossible.  Unless you bent the leaf in the switch so much the air pressure change of your finger moving near causes it to activate?  That would be pretty amazing.