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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iMac won't boot after replacing logic board

I just replaced my logic board in my 27" imac after I broke off the display port connector on my original logic board. It booted the first time I tried, but the fans were on constantly and I forgot to reattach the wifi cable so I took it apart again.

Then I booted I without the display installed to see if the fans were running normally. They were so I powered it down by holding down the power button. I then installed the display and proceeded to boot it up again.

I cannot get it to boot now. It is stuck on the apple logo with white background and the loading bar moves slowly towards the end but it never leaves this screen. I have tried SMC reset, pram reset, safe boot, boot to recovery partition, booting from external USB drive, booting to disk utility.

How can I fix this? Why did it boot the first time and now it won't?

Update 1: I was able to boot up in OS X after I reinstalled the video card. It seemed to work fine. Then it froze up today. Now it won't boot into OS X anymore. I was able to run the Apple Hardware Test and it said there was not problem with the hardware. How do I test to see if it is the video card causing the problem?

Answered! View the answer I have this problem too

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What were doing in it the first time and what did you do besides break the logic board? Do you have an external back up drive with a system on it or another Mac with a firewire port?

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I am thinking it may be the GPU because I did remove that to re-route the wifi cable. I would think that the screen would be black if the GPU was not working??

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What keyboard are you using? Wireless or wired?

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I am using the Apple wireless keyboard.

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If your Mac doesn’t make any noise at all when switching it on, or if you hear the fans running but nothing else, you may have a logic board failure. Try to replace your apple wireless keyword and then try again.

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Chosen Solution

Next time contact us first, Apple would probably have fixed it for free under this program:

iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program

https://support.apple.com/en-us/HT203787

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I don't have that video card. I have the 5750.

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To test out the video card hook it up to an external monitor. If you get a good picture the issue is further up the line.

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Hmm, thats normally what happens when the GPU is bad. Try to reattach the graphic card. What does the LED says?

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I did detach the GPU from the logic board to re-route the wifi cable so maybe the GPU is not fully in its slot on the logic board. What you mean by "what does the LED say?"

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He's talking about the diagnostic LEDs to the right of the RAM slots.

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I'll have to check that tonight.

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I opened it back up, took the logic board out, and re-attached the GPU. Now it boots fine. It must not have been completely connected to the logic board. Thanks for the suggestion!

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No problem @kasey glad it worked out!

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Seems like a problem with the video card. As you know video card is separate from logicboard. Another possibility might be the lcd cable. Check it out. Thanks.

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How do I test to see if it is the video card or the lcd cable causing the problem?

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kaseydoggett will be eternally grateful.
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