iMac 2006 No picture but GPU and LCD are OK

Hello,

I have got a working iMac 24 a1200. Everything is OK GPU /LCD are perfect.

Now I bought a dead iMac 24 a1200 on ebay. It shows no picture but the fans are turning on and the white led is on, but the LCD doesn't show any picture.

When I turn on the iMac the start tone appears and the backlight turns on but the pixels stay black (black with little glow behind). I connected the iMac to another monitor - no input.

So I swop the LCD out of the ebay iMac and installed it in my working iMac 24. It worked - so the ebay LCD must be OK.

After that I turnd on the ebay iMac without the LCD but connected to an external monitor. The iMac started nornaly and showed a perfect picture on the external monitor. So the GPU is fine.

By the way all 4 control leds are turnd on when the iMac is runnig.

What could be the problem? Is it a logic board defect? Why is the GPU not communicating with the LCD?

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Can you discern the desktop, when it is on, and shinning a flashlight at an angle to the screen.

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Thank you for your reply! I will try that.

But I am sure that the backlight is working because, when I turn the iMac on there is a gray shine behind the pixels.

Is it possible, that the logic board has a communication problem between the GPU and the display/lvds connector? But if there is an communication problem, why does it work with an external display?

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What are the diagnostic LEDs to the right of the RAM slots telling you?

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They are all running!

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Examine the capacitors (small cans) for swelling and/or leakage.

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