I am using a refurbished 30" apple display. The brightness control has started adjusting on its own to the dimmest setting. I can go into the Display window in Preferences and put it back to where I want it but it automatically goes back down to the dimmest setting - all by itself. I have tried setting it to where I want it and restarting but that does not work.
I've experienced the same thing this morning. Turned it all on, started working and the display brightness icon would appear on the screen and it dimmed slightly. I adjusted it back up. A few seconds later the same thing again. This happened several times in a row.
Then it decided to go all the way to the dimmest setting and stay there. It was as if someone had their finger on the 'reduce brightness button' constantly. I tried adjusting the brightness up again using the keyboard, the buttons on the monitor and the sys pref. All adjusted the brightness back up but the moment I let go of the button it would dim again.
I've managed to solve it (maybe only temporarily?) by following other peoples suggestions. I firstly tried resetting the PRAM. This had no effect at all so I then tried the good ol' fashioned "turn it off at the plug and turn it back on" method. Not the most technical solution but it worked!
I just hope my monitor isn't about to go AWAL... Just for reference it's a 2007 model.
Personally I'm trying to hold out for the LED replacement : ) if it ever happens....
My 30" ACD developed exactly the same issue recently. But I suspect it is a Mac OS X bug, something introduced in the latest 10.6.5 or the version before that.
Perhaps a timing issue: the display during startup tries to talk to the OS, but it refuses to talk and the display eventually gives up and switches to low brightness mode (as a safety precaution) and all buttons stop working (including the OFF button) because the display thinks the host will not listen anyway.
Of course the timing issue could also be caused by other items connected to the FireWire or USB bus.
Try rebooting without any items attached to either bus.
*Temporary Solution*
What works for me is to physically disconnect the display from the mains power, once fully booted, then wait a few seconds and re-connect the display - all the while the Mac is still on.
Maybe not the best thing to do, but it forces a reboot on the display at a time the Mac is able to listen. After that all my buttons work again. Including brightness and On/Off.
Let me know if this works for you. If so, we should submit an OS X bug report.
I've been having this problem since late 2008. (Bought the Mac Pro and 30" screen in Aug 2008, brand new from Apple). Drives me insane. I don't know how many times I've been on the phone to Applecare about it (well, actually I do, it's well into double figures).
PRAM resets, Erase and Installs (3 times), 'restarting', unplugging everything. It's been in for repair at an Apple service centre, where they couldn't find anything wrong. Infuriatingly I have a second problem with it; the 'Are you sure you want to restart your computer?' dialog also randomly appears. I click cancel, it pops back up, cancel, pops back, cancel, pops back. I eventually have to give in and restart.
(What's particularly fun is when the dialog pops up and you're typing, and you hit enter by accident, and it restarts whilst you're halfway through something important.)
Given up on Applecare, have wasted too many hours starting at square one, PRAM, "maybe we should do an erase and install" over and over. At Christmas I bought and installed a new HD, and have done a completely new install of the OS, on to which I've been diligently moving all of my programs to.
It's just started doing it again. (Both the brightness dimming, and the 'restart your computer?' dialog).
I was having the same problem this morning. Through process of elimination, I've found that it is something to do with the keyboard control. I went to Display settings in System Preferences and checked the "Disable brightness buttons" box, and the slider would stay put wherever I would set it. I then unchecked the box, and the keyboard controls work fine.
Just seems to be some random startup keyboard issue.
Thank you SO much, this worked like a charm without having to reset or restart or do anything complex or annoying! YAY! Easy fix, so glad I read to the end of this thread without trying the other suggestions first...
My 30" Apple Cinema HD Display started doing this dance yesterday and it's soooo freaking annoying. It's like the monitor thinks that the "Down Brightness" button on the side is stuck pressed-in when it obviously isn't. Thank goodness for manual override!
OP (Polly), you should mark this thread "Answered" with six_day_trial's post as the answer.
