Internal Microphone does not record sound

Hello iFixit community,

I am facing an annoying issue with my Lenovo X380 Yoga running Windows 11 (26H2):
It does not record sound using the internal microphone.

I tried every imaginable software fix:

• the device is correctly detected and does not show any errors
• it is running on the newest Conexant driver (version 8.66.89.51), but I also tried to run it using the native Windows drivers
• it is unmuted with the Fn + F4 hotkey combination
• the Level is at 100 % and Boost at +12.0 dB
• Exclusive Mode and Signal Enhancements are disabled
• access via the privacy settings of Windows is enabled for all apps

Since external microphones were working (both connected via Bluetooth or headphone jack), I considered a hardware fault. But even replacement of the microphone / camera card in the top of the screen did not help. I also checked the connection to the system board, but it seems fine.

When I got the laptop as a refurbished device, I switched the keyboard, but I'm pretty certain that the microphone was still working after that. Sadly I cannot say, when this issue started ... it was definitely some time (a year or two) ago, but didn't bother me too much.

Any ideas what else could be wrong with my system?

Every help or suggestion is highly appreciated!
Michael