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Author Topic: Keychron K3 Max number row not working  (Read 1959 times)

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Offline Inventel

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Keychron K3 Max number row not working
« on: Thu, 07 August 2025, 15:55:41 »
Hello, I purchased a used Keychron K3 Max ISO at a good price. When it arrived, I noticed that the entire row of numbers and the keys you see in the photo don't work. The keyboard is new and shows no signs of use, so I decided with the seller to keep it and pay only €10.



Can you help me fix it? The RGB LEDs all work perfectly and the pcb is only a little oiled from the switches but I can't find any problems.

Here are the photos of the PCB:





« Last Edit: Thu, 07 August 2025, 15:58:06 by Inventel »
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Offline HoffmanMyster

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Re: Keychron K3 Max number row not working
« Reply #1 on: Wed, 13 August 2025, 10:41:13 »
Approval :thumb:
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Offline zegonix

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Re: Keychron K3 Max number row not working
« Reply #2 on: Mon, 18 August 2025, 07:12:12 »
do you have access to a multimeter? if yes, try following the traces from rows and columns to the micro controller (chip under the spacebar marked as `stm32f402`). (if a trace vanishes in a tiny hole it switches to the other side)
then try to measure the resistance between the mcu's (micro controller unit) pin and the switch contact. for reference the resistance should be below 4 Ohms.
also a reasonable test is checking the switches resistance should be even lower..
if the resistance is higher or infinite the contacts (either solder joints or traces..) are damaged and need to be resoldered or repaired.

could be something different, but i would check this first.
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Offline Inventel

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  • Posts: 3
Re: Keychron K3 Max number row not working
« Reply #3 on: Mon, 18 August 2025, 13:07:48 »
Quote from: zegonix on Mon, 18 August 2025, 07:12:12
do you have access to a multimeter? if yes, try following the traces from rows and columns to the micro controller (chip under the spacebar marked as `stm32f402`). (if a trace vanishes in a tiny hole it switches to the other side)
then try to measure the resistance between the mcu's (micro controller unit) pin and the switch contact. for reference the resistance should be below 4 Ohms.
also a reasonable test is checking the switches resistance should be even lower..
if the resistance is higher or infinite the contacts (either solder joints or traces..) are damaged and need to be resoldered or repaired.

could be something different, but i would check this first.

With the multimeter in diode mode I tried to test the pins of the micro controller with the columns and I noticed that with the not working column I receive a full signal on one pin (and this is normal), but I also receive a little signal on other pins of the micro controller (this doesn't happen with the other columns pins).
Does this mean the micro controller is damaged?
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Offline zegonix

  • Posts: 110
Re: Keychron K3 Max number row not working
« Reply #4 on: Thu, 21 August 2025, 04:21:35 »
do not use the diode mode. just measure the resistance, that tells you much more than "is the resistance below ~50 Ohms". depending on how you measure, the measuring voltage of your dmm could activate the diode. try measuring the resistance and when you get a signal where there should not be one, try reversing your measuringtips.
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Offline cardon

  • Posts: 1
Re: Keychron K3 Max number row not working
« Reply #5 on: Fri, 29 August 2025, 05:11:14 »
You are now the fourth person I have come across with this problem in just the past month. The same thing happened to my board. Fortunately I purchased from Amazon and the board failed within the return window so mine went straight back to Amazon.

As yet, I haven't heard any stories of resolution on other boards with this problem.
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Offline Inventel

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  • Posts: 3
Re: Keychron K3 Max number row not working
« Reply #6 on: Fri, 29 August 2025, 05:18:02 »
Quote from: cardon on Fri, 29 August 2025, 05:11:14
You are now the fourth person I have come across with this problem in just the past month. The same thing happened to my board. Fortunately I purchased from Amazon and the board failed within the return window so mine went straight back to Amazon.

As yet, I haven't heard any stories of resolution on other boards with this problem.

Yeah, I tried messing around with the multimeter, but I couldn't fix it.

I contacted Keychron and managed to get a replacement PCB shipped to me for €40, including shipping to Europe. It arrived yesterday, and so far everything is working fine.

Considering that I spent about €50 in total (broken keyboard + new PCB), I think it was worth it.
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