Q: 27'' led cinema display adjust brightness missing
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Nov 13, 2013 1:17 PMby Malcolm J. Rayfield,Is the display's USB cable plugged into the computer? It is needed for brightness control. If that's not the problem, try the EDID Reset Tool.
<http://download.info.apple.com/Apple_Hardware_Test/EDID_Reset_Tool.dmg>
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Sep 5, 2015 6:26 AMby borisdesmond,** SOLVED **
Had the same problem on a MBA + cinema display 27" with OS 10.11 El Capitan (Aug 2015),
--> resetting the EDID with the tool above fixed the problem, thanks heaps.
I had previously reset the PRAM as well, not sure if it helped.
Tool here : http://download.info.apple.com/Apple_Hardware_Test/EDID_Reset_Tool.dmg
Note : F1 / F2 adjust brightness of your main screen, Control F1 / Control F2 adjust brightness of your secondary screen.
--> This wasn't working previously and has been restored by the EDID reset as well.
