Last week I moved my home office, which consists mainly of a desk with a MacBookPro and a 7 years old 20” Cinema Display, from the room downstairs to another room upstairs.

Unfortunately when I plugged everything back on, the Cinema Display didn’t turn on, and the power light was flashing with the “short, long, short” code, which means “Make sure you are using the correct power adapter with the display”. Of course, since I’ve been using the display for 7 years, the power adapter was the right one.

Apparently this problem is very common, and looking on Google and on Apple discussion support forums there are hundreds of people reporting the same problem. The solutions varied from sending the display to repair for 400USD (apparently some problem with the display’s board) to buying the upsized power adapter (the one for a bigger display) for 150USD.

But one guy also suggested this nice zero-cost solution:

It turns out the middle pin in the power connector is a ground. When it read an incorrect voltage it makes the displays inverter turn off to protect the unit. One way to circumvent this is to cover the middle pin in the cord going from the monitor to the power brick. I used a piece of paper in the shape of a “W” covering just the middle pin. I double folded a piece of paper and folded it over the plug and down into the connector and then gently pushed the plug into the power brick. Once i did this the monitor popped on and all was good in the world…

This made the trick, and now I’m happily typing looking at my Cinema Display.

If the explanation is difficult to visualize, I found a video on Youtube the shows how to do it (it uses some tape instead of paper, but the concept is the same).