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모델 A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 또는 2.8 GHz Core i7 프로세서

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iMac mid 2011 21inch black screen after cpu upgrade

So i have an iMac 2011 21inch that originally came with intel i5 2400s CPU, decided to upgrade to i7 2600cpu, even though it takes 95w of power instead of 65, people say its possible to do this upgrade on this machine. So, i followed guide on ifixit on how to change cpu and i assume i did everything very accurately. Upon first start, i hears usual startup chime, a screen backlit flashed on and off and then heard fans working hard but black screen. Held power button until it turned off and tried again, this time same scenario but no backlit flash - screen completely dark, heard start chime with optical drive sound and fans working hard. Im pretty sure its not the backlit turned off but something else. Checked all display connectors and they connected properly and are tight. Also tried the command option p r combo, i do hear iMac restarting a lot of times as long as i keep holding the combination. Once released - it supposedly boots up. Any suggestions? Put old cpu back?

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Did this ever get resolved?

Please @andriivarko, let us know if you fixed this. Read my comments below on my 2010 -21" failure. I tried something similar with the same result.

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I would put back the original CPU to see if all is good again. I am not sure the logic board can handle 95w. That is a lot more than 65w. I had the same issue with 2010 iMac i3 upgrading. Even if the CPU fits physically you can as everymac.com writes: "...one only can upgrade the processor in an Aluminum iMac with a socket-compatible processor that has the same, or lower, TDP as the originally installed processor." So it can be that the BTO i7 model has different specs.

I searched but could not find anyone that successfully upgraded the 2011 iMac 21.5" from i5 to i7 CPU.

Of course there can be reasons for the fans blowing,

- the CPU temp cable is loose

- the LCD temp cable or other cables are loose

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I tried almost exactly the same thing. I switched out the original i3-550 with an i7-870 - but I got the exact same black screen on boot. I hear the fans start but the screen never comes on. I've tried everything I can think of to no avail. My understanding after some research is that the New processor has to match or be below the processor TDP (thermal design power) So the i7-870 has a 95W TDP - but the 2010 iMac only supports up to a 74W TDP processor.

That being the case, the best processor you could upgrade a 2010 iMac to would be the i5-680.

However, my understanding is also that the 2011 iMac supported an i7 processor in one of the original Apple configurations - and therefore most likely has a higher TDP support than the 2010. You might be able to get something more powerful into the 2011.

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This is the only i7 that will work in the 2011 21.5" system: i7-2600s. The 27" model offered a i7-2600 chip which has a higher TDP than the S version. Which is why the system won't start. Basically the wrong chip.

@Dan is right. On both 2010 and 200 models the 27" iMac supports higher TDP than the 21". The 2010 -21" iMac was not offered with an i7 but it was an option on the 2011. I am not sure what happens when you put a CPU in that draws 30% more power (something could be fried). @pixelworldI did the same thing as you in a moment of eagerness. Had not investigated enough the difference between the 27" and 21" 2010 models. Black screen on startup, fans crazy.

I put back the original CPU and after a lot of checking was able to get the iMac to start up normally. Still the black screen but worked fine on external display.The internal LCD was not recognized in system information. I did not have another LCD to test if that had been damaged by the CPU change. Could have been the backlight. I usually never give up but this one I just sold as-is to get sleep at night again. I really felt so stupid that I had not investigated this better. Some lessons are more expensive than others! I would check any way the LVDS connection and if you have a chance to swap with another LCD. Would be great to hear if you solved this!

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Hi guys, I did upgrade from i5 2400 to i7 2600 for my 2011 IMAC 27" , they are both 95 TDP based on my research, however, after the installation, the screen went to black when I was trying to power it up, and after around 10 seconds, the fans were running on full speed without stop. And the screen kept black. Anyone knowing how could this still happens when the CPUs are at the same TDP?? And I have known that someone has successfully upgrade from 2400 to 2600 with no such problem what so ever. Really need some help here. p.s. I also added a SSD used OWC cables and upgraded to 16G RAM, but I don't think these upgrade could cause the above problem as I have replaced the original RAMs back and also unplug the SSD which I added, but still not working......please help!!!

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There's more to it than TDP!

You need to review Intel's ARK listing on your original chip and then compare what your options are based on TDP, Bus Clocking, and if needed graphics services depending on the chip being replaced.

@Dan is right. Check again the CPU specs. Are you sure the original TDP is 95 and not 65? You need to check that and take it all apart and carefully assemble it again. From my experience something is not compatible. It is not getting past BIOS negotiation since the fans are crazy and screen is black. Hopefully you have not damaged anything. Try to put back the original CPU. It could also be a bad CPU if your information og TDP is correct.

Dan & Asle, thanks for the replying, About the CPU, this is the only part which i didn't restore to its original status as its quite a job to do. However, hearing the Chime means the CPU is running? and I also confirmed this with a Apple Store staff. Besides the CPU which I installed was i7-2600 which is exactly the premium upgrade for mid 2011 IMAC 27 from Apple online store itself so I really don't think it's due to a compatible issues here. And if the CPU was original broken then I won't even hear the Chime. Right? But now I'm stuck here as the Apple store won't help me to check the problem as I personally modify the IMAC plus its not under the warranty. I'm trying to google for more information and now only found few people had similar problems but only in 2011 IMAC 21 inch after i7-2600 had been installed, that might be causing by the higher TDP, but for 2011 27 inch IMAC, everyone else had achieved it successfully apart from me. Thanks for you trying to help me here and I'm still not giving up yet.

Before you do the upgrade did you check the systems firmware? Here's a link to the Apple T/N: About EFI and SMC firmware updates for Intel-based Mac computers.

Now the rub ... Do you have the older version or a newer one? Sadly, you'll need to put the original chip back in to find out as well as update, if needed.

Sorry to say I don't know if the newer firmware is the cause or if the older is.

Hi Dan, I did't check the firmware before the update. But I often updated followed the App Store reminder, is this EFI and SMC firm updates a part of the App Store updates or it's a separate thing? And could this update either newer or older one can cause the black screen? thx

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