Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7

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Black Screen iMac 27

Hy ,

I have an Apple iMac "Core i5" 2.8 27-Inch (Mid-2010)MC511D/A.

When I press the power button i have a black screen, the fans are spinning, backlight working, you can hear the gong. How can I diagnostic a faulty motherboard or a faulty video card? I have already tried with an external monitor, but no signal.

Any ideas ??

Update 12/17/16

Caps Lock LED on wired keyboard doesn’t light when pressed.

I have checked the Diagnostic LED's and all 4 are on. LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found. If the fourth LED is not visible after power on:

  • Verify cable connections between LCD panel and logic board
  • Inspected LCD display cables for cable damage
  • Verify external video functionality, and according to result check the following items:
    • If external display works then verify/replace the LED backlight board
    • If external display works then verify/replace the LCD panel
    • If external display does not work verify/replace the logic board

Please, any suggestion what should I check before changing the logic board. I still suspect the graphic card .

Answer this question I have this problem too

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Either aim a flashlight into the screen at a sharp angle are you able to see a faint image of your desktop? Or try using an external display any image on it?

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Hy ,

I have already connected to an external display and no signal , with a flashlight can't see anything .

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Ouch! Not good.

Yes, it sounds like the graphics card is bad.

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I suspect the graphics card and the logic board. I take the graphics out and I will go to a service to check it. But because it has a temperatures sensor I think it should enter in protections mode when the heat is too hight .

Is it anything which can be tested for a better diagnose?

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The diagnostic LED's is about it. If you had a schematic and logic board layout you could poke around with a DVM to measure the power rails and if you had a scope you could look at the other signals.

For us mere mortals it's mostly isolate it down as best as you can (which you did here) and start swapping things out.

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Raul will be eternally grateful.
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