iMac Mid 2011 27" black screen after cpu upgrade

Discussion in 'iMac' started by paul315427, May 25, 2016.

  1. paul315427 macrumors newbie

    May 25, 2016
    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. I can heard the Chime sound every time when I started it up but the screen just kept completely 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 on and also unplug the SSD which I added, but still not working......please help!!!
  2. hfg, May 25, 2016
    Last edited: May 25, 2016

    hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    Hearing the chime is good after a CPU change. At least it is running that far into the boot sequence.

    You might check all the cables to be sure they were replaced properly and without damage. If you added a SSD in place of the hard disk and are trying to boot from it, you will of course, have to format the SSD and instal the OS onto it.

    The fans running full speed are probably not heat related, but due to either a system crash or cable issues. The RAM upgrade could also be an issue. You have so many new variables it is hard to diagnose. You may have to revert back to the old drive and RAM and verify that just the CPU upgrade is working, then add the disk and RAM one at a time to see where the problem really is.

    BTW: quite some time ago I added a OWC SSD to a iMac in addition to the hard disk. Everything worked fine for awhile, then the iMac went pretty much dead. I was sure the main logic board had probably developed a problem, so I took it to a local authorized dealer to diagnose and repair under warranty rather than taking it apart again myself. Was I surprised when he called and told me the SSD had failed, and in such a way that it totally blocked the computer from running at all. Simply unplugging it brought the iMac back to full operation, and replacing the SSD with a new one also worked fine up until I sold it.
  3. paul315427 thread starter macrumors newbie

    May 25, 2016
    hfg thanks for the replying,

    About the installation, I followed the instruction on OWC website step by step, so shouldn't had any damage or wrong connection as I think so far. But I will check again, for the fourth time:(

    About the SSD, at first I thought it might be the SSD which I added was broken somehow although it's brand new. So I disconnected the SSD but it won't fix the problem.

    About the RAM, I also put the original RAMS back on, problems stays. and based on OWC staff replied, it shouldn't be the RAMS causing neither the black screen nor the fast running fans as it normally has the BeeBee sound instead of Chime sound if the RAMS goes wrong.

    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 as you mentioned above, I thought the same 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, and I don't know how to test which part might goes wrong as there are too many parts inside and even a small cable might causing the issues.

    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:( really sad about it.

    But thanks for you trying to help me here and I'm still not giving up yet.
  4. Easttime macrumors 6502a

    Jun 17, 2015
    Ugh. I got an SSD kit from OWC to replace the spinner HD in my mid-2011 iMac. Followed the instructions carefully. Seemed to go well, but screen is black. Can hear the chime and judging by the second monitor the system boots fine. Took it to an authorized dealer who is trying a replacement screen. First time I've had a problem doing my own work on a computer in 20 years.
  5. hfg macrumors 68040


    Dec 1, 2006
    Cedar Rapids, IA. USA
    My guess based on the limited information would be a cable not seated completely (assuming no cables were damaged during the disassembly). I think your CPU is working and the TDP has nothing to do with your problem at this point. Do you have a Apple Authorized Repair shop nearby other than the Apple Store? They might be able to fully diagnose the problem out of warranty which the Apple Store won't do.

    When you unplugged the SSD, did you disconnect the actual cable from the motherboard itself? The story I mentioned above was with a 2011 iMac and somehow the SSD produced a fault at the SATA port which disabled the whole iMac such that it wouldn't boot from any drive, internal or external, or the optical drive. I suppose a faulty SATA or Power cable could also affect the SATA port in a similar manner even with no drive attached.

    Good luck ...
  6. stuartak macrumors member


    Feb 21, 2016
    You may not like the answer but I have modified lots of machines , so I would suggest the following , remove everything you have installed and revert to your original configuration and check that the machine works, the fact that the machine chimes does not prove the cpu is ok , just that it passes post. Once back to scratch I would upgrade the processor and check its ok. Then upgrade the ram and check , then install the ssd . I assume from what you describe you are not booting from the SSD and that OSX is installed on the HDD? . Unfortunately you have upgraded lots of things at the same time which can be trouble some . It only needs one connection of the thousands involved with CPU's and ram to be intermittent to give all sorts of strange problems , my advice is baby steps and test.

    Also I assume your i7 2600 is used , and whilst cpu's rarely die easily its always possible .

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5 May 25, 2016