LED Cinema Display (27-inch): Intermittent loss of audio
You may notice that sound from an LED Cinema Display (27-inch) connected to a Mac intermittently becomes inaudible. In some circumstances, you may need to unplug the display and reconnect it or restart the Mac before the sound becomes audible again.
- Make sure the USB connector on your LED Cinema Display (27-inch) is physically connected to your Mac.
- Run Software Update by opening the Apple () menu and choosing Software Update. The updater application will download to the Utilities folder and should run automatically. You can also manually download the LED Cinema Display Firmware Update 1.0, then double-click the updater application to begin the installation.
You may need to repeat these steps to install this update on more than one display.
Note: Do not turn off or unplug the display while the updater is running.
To verify that LED Cinema Display Firmware Update 1.0 is installed on your LED Cinema Display (27-inch), double-click on the updater application in the Utilities folder. If the firmware update has been successfully installed, a message will appear indicating that the firmware is up to date.
The message "No updatable device found" may appear if you run the updater application manually without an eligible display connected to your Mac.
In some situations, plugging headphones (or iPhone headphones) into a Mac connected to an LED Cinema Display (27-inch) will limit the audio output choices in the Output tab of the Sound preferences to headphones only. This is known as headphone redirection.
For Mac Pro computers, you need to switch the analog line-out port, optical digital out port, and external audio devices (such as USB or FireWire) manually using the Output tab of the Sound preferences. This is due to the discrete audio engine these computers use for audio processing.