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27" display with 2560 x 1440 pixels resolution Thunderbolt & MagSafe cable attachments

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How do I know whats wrong?

I have two of the same apple displays connected to my laptop. It used to all work but one stopped working. I tried trouble shooting. All the ports in the back are working. When I go to display in system pref. it show all three screens. I have even hooked up the bad one to my comp and then plugged the good display into the bad one and the good display works fine. Do you think it is the actual screen or could it be simple like the cable?

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crwdns2853045:0crwdne2853045:0 crwdns2853046:0crwdne2853046:0
crwdns2889612:0crwdne2889612:0 -1
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If the cable looks damaged then that could be the issue. But from what you described here I suspect the display logic is having a problem.

Lets try this with the display plugged in and on, shine a flashlight directly at the screen (you'll need to hold it right against the screen at a sharp angle) are you able to see a faint image? If you do, the backlight circuit is having a problem.

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crwdns2889612:0crwdne2889612:0 1
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jestey crwdns2934231:0crwdne2934231:0
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