The brightness control button is not working, what could be wrong?

[lovecd]

The brightness button on my Apple 30" Cinema Display is not working, try to do the adjustment through Mac OS, but can't find it over "Display" menu either, what could be wrong here? Is it easy to be fixed?

Many thanks!

 

[joevt]

Are you using an M1/M2 Mac? I think Apple didn't make compatible its brightness control code for the Cinema Display on Apple Silicon macOS.
Is the USB connected? The brightness control requires the USB connection.

If you are using an M1/M2 Mac, or cannot connect the USB cable because it's broken or the current version of macOS doesn't like it on your particular Mac (one of those is true for me - a recent development...) Then you can try MonitorControl.app which will do brightness control using DDC/CI instead of USB. You may need to set the maximum brightness value in the MontorControl.app advanced settings. #95

 

[lovecd]

Are you using an M1/M2 Mac? I think Apple didn't make compatible its brightness control code for the Cinema Display on Apple Silicon macOS.
Is the USB connected? The brightness control requires the USB connection.

If you are using an M1/M2 Mac, or cannot connect the USB cable because it's broken or the current version of macOS doesn't like it on your particular Mac (one of those is true for me - a recent development...) Then you can try MonitorControl.app which will do brightness control using DDC/CI instead of USB. You may need to set the maximum brightness value in the MontorControl.app advanced settings. #95

I'm not using M1/M2 laptop, just the old 2008 Mac Pro, running Catalina OS. I suspect something wrong with the hardware on Cinema Display, but will try that Montorcontrol app and see if it can be adjusted there.

Thanks,