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iMac 27" 2017 screen at 40% brightness

I have a 27" iMac 2017 running Catalina with a screen that occasionally does not go beyond 40% brightness. The keyboard function keys and the system preferences display slider indicate the screen is at 100%, but using either does not affect the screen brightness until I get to the 40% level, and below that it will dim further. I do not use the auto brightness adjustment option.


Sometimes resetting the SMC works, sometimes it does not. I had this problem prior to upgrading to Catalina and was hopeful that the upgrade would eliminate the problem. My hopes have been dashed.

iMac 27", macOS 10.12

Posted on Feb 7, 2020 6:53 AM

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Question marked as Top-ranking reply

Posted on Feb 7, 2020 6:56 AM

Try an NVRAM reset:

Reset NVRAM or PRAM on your Mac - Apple Support

5 replies

iMac 27" 2017 screen at 40% brightness

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