This morning I was greeted with a blank screen and the power light flashing short-long-short, and groaned at how expensive today was about to get.
The Apple support page states that this flash pattern indicates the wrong power adaptor is being used with the display. I’m using the original 90W adaptor supplied with the screen and keep it powered via an APC UPS.
Fortunately with a bit of googling I found the ‘paper w’ solution here and on the post by jakobeon on the Apple disscusions forum. Essentially by using a strip of paper to blank off the middle of the 5 output pins from the power brick, the display is back to life.
From reading through comments made by others in both forums, and scanning over the power adaptors page, I’m forming the following conclusions. (Note: these are my guesses based only on my interpretation of other’s anecdotal evidence rather than anything authoritative).
1. I suspect the middle pin is used only to allow the monitor to sense which of the 3 Apple power-bricks is attached. If so then it seems more concerned with protecting the monitor from a low power brick, rather than from being overloaded somehow.
2. A number of people have indicated that simply replacing the brick like for like or with the higher power version makes no difference. This suggests to me that the fault is within the electronics of the monitor, when detecting the power source at switch-on, rather than in the brick.
So while this is far from an ideal solution, it is cheap, simple and quick to implement compared with trucking everything back for repair. However if in doubt, get it repaired by Apple – don’t blame me if your house burns down.