Currently Being ModeratedJun 29, 2011 4:56 AM (in response to citan)
maybe you changed the behavior of the Function-keys accidentally.
Have you tried the keys with the 'Fn'-key ?
Currently Being ModeratedJun 29, 2011 5:01 AM (in response to Fortuny)
i should write it in the first post. Brightness controls work fine if iMac is not connected to MacBook, do not work when connected to MBP.
Currently Being ModeratedJun 29, 2011 5:43 AM (in response to citan)
Maybe a SMC-reset http://support.apple.com/kb/HT3964 can help
Haven't had such problem myself yet.
Currently Being ModeratedJun 29, 2011 5:47 AM (in response to Fortuny)
Ah, i forgot to write it in the first post. I did it, didn't help.
Currently Being ModeratedJun 29, 2011 6:03 AM (in response to citan)
You don't seem to be alone with it https://discussions.apple.com/message/15515094
Currently Being ModeratedOct 31, 2011 7:57 PM (in response to Fortuny)
I posted this in the linked discussion thread above, but just in case it might help someone finding this thread:
I've futzed with this for a while using a MBP and an iMac, both running 10.6.8. The problem is inconsistent for me, but seems to be linked to how long I've had the iMac on. If on chronically (as I usually leave it), the iMac tends not to respond to F1/F2 brightness keystrokes when I connect my MBP and use the iMac in target display mode. But if I reboot the iMac and then connect from my already running MBP, this restores brightness keystroke response. That is:
1) With MBP and iMac running, connect mini DP to start target display mode on iMac
2) If brightness keystrokes don't respond, disconnect mini DP and reboot iMac, leave MBP running
3) After booted to desktop on the iMac, reconnect mini DP - brightness keys should respond
This has worked consistently for me. Hope it works for you, too. Hope Apple fixes this permanently somehow soon, it sure is annoying.
Currently Being ModeratedFeb 2, 2012 10:11 AM (in response to citan)
If you have a wired keyboard, plug that into the iMac and use the brightness keys to get your desired brightness. You can do this while the iMac is the second monitor. Worked for me.
Currently Being ModeratedJan 8, 2013 8:10 PM (in response to citan)
I had the same problem with 10.6.8. But it works well with the mountion lion upgrade.
Currently Being ModeratedApr 21, 2013 9:02 PM (in response to 36Joules)
DUDE - you're a genius! Thanks for this, I've been squinting for the last month because of my bright iMac (aspecially at night) and I'm on deadline so HAVE to work all night...
Thank you thank you thank you!!!!
Currently Being ModeratedMay 5, 2013 2:15 PM (in response to citan)
ONE MORE SUCCCESSFULL SOLUTION. I have iMac 27" with Mini DisplayPort used as an external monitor for Macbook Pro Retina 15" with Thunderbolt port connected with MDP cable. After the iMac system was automatically updated to version 10.6.8, the brightness stopped adjusting by pressing F1 and F2 keys on the wireless iMac keyboard during the connection. I've tried to reboot iMac in different special modes, reseting, etc..., but all the attempts failed. Finally I've remembered that I still have the original istallation disc with the older OS X version, that was provided with the iMac. I've used it to install OS X 10.6.4, and got all the brightness functions back, constatly working after each reboot. Of course, it would be better to have the same functions in the latest OS version, but now I'm quite happy to get the external monitor mode properly available again.