MacRumors is reporting the availability of a new firmware update for Apple's discontinued 24-inch LED cinema displays, which addresses intermittent flickering when the displays are connected to Thunderbolt Macs. The update was privately issued to some users who contacted Apple support about the issue, and in a discussion thread at the Apple support communities one of these users posted a link to the update after having received it via emial correspondance with Apple's second-tier support.
Apple Discussion user "spunky_lausanne" describes the interaction:
"I got this update from Apple's 2nd level support. I have an open ticket since quite a while and called them probably 10 times in 2 months. This afternoon I received a phone call from them telling me that the problem was still under investigation but no solution was found yet. A few hours later I received a mail with the link I've posted previously."
The update is a small ~926KB disk image that resides on Apple's official support servers, and can be downloaded from here.
Descriptions included with the update provide some detail on what it is for, in addition to to covering situations where the problem may still persist, and also warns against applying the update with peripherals attached to the system:
The 24-inch LED Cinema Display Firmware Update addresses an issue that may cause intermittent display flickering. This firmware will only install on the Apple 24-inch LED Cinema Display when it is connected to a Thunderbolt-enabled Mac.
This firmware update may not resolve the flickering issue if a Mini DisplayPort extender cable is used.
Some USB and FireWire devices may prevent firmware updates from installing correctly; disconnect non-essential devices and use only an Apple keyboard and mouse to apply the update.
After applying the update, a number of affected users reported that the flickering seems to have disappeared.
While it is unconventional for Apple to issue updates separately from Software Update or via its support pages, the update is a legitimate one from Apple. Besides the publicly released updates, the company may have a library of updates that address both obscure problems and those that have not been fully tested, which it may periodically supply to users who experience these specific problems. Once the issue has been investigated more the update may be made available in a more public manner, but for now is only available via the link above.
Since the update has not been made public, it may be best to only apply it if you are specifically experiencing flickering when attaching your 24-inch display to a new Thunderbolt system. If your monitor is working fine, then we advise you leave well enough alone and not apply the update.
UPDATE: Apple has removed the linked file from its servers, so it is no longer available for download. It may be likely that users affected by this issue can get the updater directly from Apple support, but for now it can no longer be directly downloaded. Apple may prepare it as a full public firmware update for users in the future, though there is no indication of if or when this will happen.