Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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iMac 21 will not boot after CPU change

I bought a Intel Quad-Core i7 875K CPU to replace the 3.2Ghz i3 in my 21" iMac 2010. This is specifically the same as the Intel 870K in the guide here on ifixit. I followed the guide and was careful to assemble everything back, all cables and screws.

Now the iMac will not boot. The fans go on but there is no chime and no picture on the screen. Is there anything that could cause this? When I look at the LCD message lights on the logic board, Light 1 and 2 are on only.

I now tried to put back the i3 CPU and the iMac behaves exactly the same. I wonder if I have damaged the LVDS cable that connects to the logic board. Could this be the reason it does not start and only turns on the fans?

I would appreciate any thoughts about this. Maybe someone experienced the same.

##UPDATE##

The iMac is booting just fine now. I bought a new LVDS cable. The connector on the logic board seems fine to me. But there is no picture on the internal LCD and when I connect an external monitor I see no internal LCD in the displays in system configuration, only the external monitor. I would avoid buying something that is not broken but I have no other LCD to test with. Does it seem the logic board can be damaged? Should I try to change the GPU?

The LED lights on the logic are lit, 1-2-3 , but not 4.

Answer this question I have this problem too

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I think I was able to connect the LVDS cable now. I detached it from the LCD and connected it carefully to the logic board. Now these 3 lights are lit on the logic board. 1 - 2 - 3.

Still the fans start going pretty high, but there is no chime, no light on the screen.

I am still running the original i3 3.2Ghz and not the new i7 CPU. I think maybe this will not work since it is 93watt and the i3 original is 74watt. I see now that all the guides refer to upgrading the 27" iMac 2010 which indeed was offered with this CPU.

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Try putting back the old processor and then check the systems firmware is the most current. Did you verify the chips specs from Intels ARC web site?

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I put back the original i3 CPU and carefully went over all the cable connections. Still it does not give a startup chime, meaning it is not even loading the firmware (I guess?). Like I wrote I discovered to late (too eager!) that the watt usage was different from the 27" iMac. But could booting up the iMac with the i7 CPU have damaged the logic board so much that it will not even load firmware? Strange then that the diagnostic lights are on? First 1, when I power on -2, then after some seconds light 3. Any idea where I start to check now? Do you think my logic board is fried?

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More likely it was just not a compatible chip so it damaged the logic board. Intel has a few sockets which look the same but are different. Sorry ;-{

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Is there any way to check if the logic board is damaged? Can the diag. lights still light up if the board is damaged? I now have lights on 1, 2 and 3.

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Your logic board doesn't support that stone. The guide you followed is for a supporting logic board for 27" iMac. You can only bump your iMac up to i5. Hope it helps.

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Yes, that is what I found out later. The guide is for 27" iMac which supports 93watt CPU while the 21" does not support it. I uses the i3 or i5 74watt CPU. I just wonder if trying to boot the iMac with the 93watt i7 could have damaged my logic board?

Thanks for your answer but my problem is the iMac will not boot, even no startup chime. That is what I need advice on.

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Hopefully it seems I did not damage anything with the i7 CPU. Anyway after carefully going over everything and plugging in again the iMac is now up and running. Just waiting for new LVDS cable. Learned a lesson. Read guides more carefully!

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asle will be eternally grateful.
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