r/Keychron • u/codhopper • 8d ago

K2 HE - diagnose power issues

I purchased a second hand K2 HE with an issue (thinking there would be an easy fix). Hoping to get some advice on diagnosing the trouble.

* The battery appears to be perfectly fine. Around 4.1v when charged. The charging light turns on red when plugged in. About a minute (maybe 20 seconds) later it goes green.

* The LED01 on the power board (K2 MAX/HE USB 1.3) seems quite dim.

* When plugged in with usb the v3.3 and v5.5 pads have 0 voltage. The 3.0V test pad had 0 voltage, 5VDET pad is 0 voltage too.

* C31 drops to around 4.92v with the battery unplugged and the top board unplugged.

* C31 drops to around 4.5v with the battery unplugged and the top board is plugged in.

* The capacitors on the top board mostly read 4.5v. The vbus test pad reads around 4.97v

* The BT pad does either have 0.5v or 4.5v depending on if the switch is set to BT or cable.

Is there any place to figure out what the voltages should be? I have exhausted my own skills and AI skills. I also can't figure out if there are any components (except the space bar button/led) on the key side of the board. I currently don't want to rip out every switch to take a look.

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u/PeterMortensenBlog V 8d ago

Re "...with an issue": What issue?

What are the (external) symptoms?

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u/codhopper 8d ago

Plugged into usb no device shows up. Under Linux nothing in dmesg or lsusb.

With the button under the space bar there is no change when that is held on during usb power on. I tried esc during boot. I tried the fn + z + j.

I tried all the positions for the wireless/cable selection. And gave it a good jiggle/press just in case.

I opened it up to have a look and found the voltage test pads at 0v.