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Lost Ability to Change Display Brightness

Just now I noticed that I'm no longer able to adjust the brightness of my display (a 23" Cinema hooked up to a Radeon X1900 XT). Mac Pro, quad 3.0 GHz, 10.5.1.

When I open the Displays preferences, there's simply no brightness slider. When I press the buttons on my keyboard (F1/F2), nothing happens. When I press buttons on the side of the display, nothing happens.

I've logged in as other accounts and they exhibit the same problems. WTF?

P.S. Console spits this out:
12/22/07 10:16:08 pm [0x0-0x193193].com.apple.systempreferences[9914] objc[9914]: Class O3Panel is implemented in both /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/ Authorization.monitorPanel/Contents/MacOS/Authorization and /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/ TVOptions.monitorPanel/Contents/MacOS/TVOptions. Using implementation from /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/ TVOptions.monitorPanel/Contents/MacOS/TVOptions.
This leads me to wonder if this isn't a Leopard bug I've just not noticed until now.

Update: I found the solution here. Simply put, you should have the display's USB cable plugged in. The console errors even vanish. Lame.

4 Responses to "Lost Ability to Change Display Brightness"

  1. Boo! That is unfortunate.

    While the behavior could certainly be better -- those console messages are certainly bug worthy -- the underlying problem seems to likely lie with DVI.

    Speaking rather cluelessly, does it provide a standard via which out-of-band data can be passed?

  2. bbum said on December 28, 2007:

    While the behavior could certainly be better -- those console messages are certainly bug worthy -- the underlying problem seems to likely lie with DVI.

    Indeed, the message could be better. The console errors led me to believe it was a software issue - perhaps a slightly borked Tiger->Leopard upgrade - when it's a hardware issue plain and simple.

    Radar Bug #5664438.

    bbum said on December 28, 2007:

    Speaking rather cluelessly, does it provide a standard via which out-of-band data can be passed?

    It must be something like that. It doesn't surprise me if I think about it - the earlier ADC connector sent USB signals over the same wire as the DVI signals, so perhaps we're letting that "one cable" thing toy with our minds. After all, it makes sense that information like this isn't part of the display signal and thus has to be sent separately.

    The reason I unplugged the USB cable to begin with was because I'm trying to track down a consistent crashing and "funny drawing" problem I've been having since applying the ATI Radeon X1900 XT Firmware Update.

  3. Today this was marked as a duplicate of bug #5789058.

  4. Thanks for the fix.. this has been bugging me for ages. (I should probably just upgrade my monitor, eh?)


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