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Model A1311 / Mid 2010 / 3.06 및 3.2 GHz Core i3 or 3.6 GHz Core i5 프로세서

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No picture, fans running, possible failure?

Hi there,

I have an iMac 11,2 (A1311) here, after turning on the iMac, there is no picture showing up, no typical Mac chime, Diag LEDs onboard showing LED 1&2 coming up, LED 3/4 is dark. I already changed the video card, same result. Connectors are fine, nothing broken. Unfortunately I think that the LogicBoard is defective, but as a replacement is very expensive, I hope that someone might have another recommendation/ tip?

Thanks,

Marcus

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Case solved- it was the processor which was faulty, I replaced it with a i5 3.6 GHz, and it´s working fast and reliable.... a processor health checking routine within it´s diagnose LEDs, that´s what I am missing :-)

I am aware that swapping the processor is not a regular option, but if I have a choice of replacing the processor or buy a 400 EUR+ replacement board, well...

So I hope that this may help others to fix their iMacs!

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I just had a similar model with the exact same situation. You might have an opportunity that I did not to attach an external display. I believe if the external display works then the video card is the culprit (not cheap, either).

This is just my guess but since it seems similar to what I just worked on and I could not get it to boot from an external or boot into target mode I'm assuming it's logic board related.

I would be grateful to hear from someone else on whether this is a logical thought process or if it is possible/likely that a malfunctioning/broken video card could keep the machine from booting to OS at all.

Sorry, I couldn't give you any concrete advice but Apple suggests replacing the video card first, then the logic board in the case of Diagnostic light #3 failing.

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Thanks for your answer, but I think that the external display will also not work. The video card provides the internal and external video signal, so if LED 3 and 4 is not showing a signal, it won't work.

My conclusion:

1) The new video card is maybe a DOA, I will try to verify this

2) The CPU is defect

3) Logic Board defect

As I do not have an equal system to test the CPU, does anybody has a tip how to test the CPU on the Apple logic board? I would assume that if the logic board has a defect it would work and show other symptoms like intermittent failures, high spinnig fans ec..

Is this reasonable? Customer description was that the iMac suddenly went off. Did anyone experienced the same?

Thanks,

Marcus

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When I first read your post I misunderstood you changing the video card to mean you reseated it. If you changed the card and Diagnostic lights haven't changed than outside of some obscure tips it's most likely the logic board.

Here is the official diagnosis for your particular machine.

...If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

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Also, if you have already tried AHT, replacing RAM, disconnecting airport cable, option boot, and disconnecting optical drive the last test before officially diagnosing as the logic board is to take out the coin battery in back of the logic board for 1-2 minutes, reinstall and reboot.

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I could not use AHT or any other SW diagnosis because the iMac won´t turn on. I even changed the coin battery, same result. My only hope is that maybe the processor has a failure, that´s the last thing you could exchange before exchanging the complete logic board. Unfortunately Apple does not signal a defective CPU via the diagnostic LEDs (I guess due to the fact that this is not a normal service option). From my experience, if the logic board is defective, it would show more like intermittent failures, like shutting down, high spinning fans ec.., but if no one can give me a hint how to test the CPU itself (without another good known logic board), I guess I have to exchange the complete logic board...

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could also be the display or display connector not attached

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Don't think so, otherwise LED 3 would come up and the Mac chime would be there... I also have no picture/reaction on an external Monitor

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Perhaps far fetched but.... I had the same problem with a mac book pro. Difference with the iMac is that the videocard of the mbp is soldered to the logic board.

I solved it by baking the logic board at 200 C for 10 minutes and let it cool for 20 minutes with the oven door slightly open. Then I took it out and left it for the day as I had to go. Later that day I put it back and it works like a charm!

Many people have done this already, instructions available on you tube, look for 'bake mac logic board' or similar texts.

Have fun!

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