Keychron K3 Max number row not working

[Inventel]

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:

[HoffmanMyster]

Approval

[zegonix]

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.

[Inventel]

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?

[zegonix]

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.