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Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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Screen backlight blinking when turning on iMac, then returns to normal

Guys, I have this imac late 2009, what happens is that when I turn it on, the backlight blinks for a few seconds, then the screen works perfectly for hours, however, when I turn on the computer with the screen brightness at maximum, the backlight it has more difficulty staying lit, so I need to turn it off and on again until it manages to stay lit, when I turn off the Mac with the lowest brightness, I can turn it on again.

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@ramonferre18311 all you have to do is measure the output voltages on CN3. If those stay stable, you know it's your backlight strips. If they don't, you know it's your LED board.


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A common issue in this series is the LED driver board needing repair or replacement here's the guide to get to it iMac Intel 21.5" EMC 2308 LED Driver Board Replacement Often the MOSFET's or capacitors need replacing.

Here's one source for the part iMac 21.5" LED Backlight Board Apple P/N 661-5304

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Thank you very much! I was thinking that it could be a problem with the power supply or the LCD backlight itself when it was turned on, but now I feel confident buying a new backlight board. When the new LCD board arrives I will complement the answer.


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Ramon Ferreira will be eternally grateful.
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