2011 iMac - CPU fan @ 4000 RPM, graphics lagging

Discussion in 'iMac' started by AlarmClock, Nov 6, 2014.

  1. AlarmClock macrumors newbie

    Nov 6, 2014

    Back in June, I installed a 500GB Samsung Evo SSD in my 2011 iMac via this guide, and upon booting up after the installation, my CPU fan began to whirr at nearly 4000 RPM, which is terribly loud and an incredibly faster speed than it ever reached before.

    After looking through several forum threads, I reset my PRAM and SMC, but with no results. I realized this could be attributed to a bad internal thermometer, but that's not all that went wrong...

    My graphics are now terribly laggy. I previously got 120+ FPS in Minecraft whereas I now get ~18. Many other games are unplayable due to graphical lag. Even system animations like switching desktops in Mission Control frequently stutter and never have optimal framerate.

    Again, this didn't happen over time, but immediately after installing the SSD. I've since opened my iMac and replugged in all the wires, to no avail. I also unplugged the SSD and booted up to my HDD, but the issue still remained.

    Any help that can be provided is greatly appreciated, as my $2000+ machine is now loud and laggy, whereas it was almost silent and super smooth previously.

  2. omvs macrumors 6502

    May 15, 2011
    Is it definitely the CPU fan?

    I had screwed up the LCD datacable during an upgrade, and the ODD fan (and maybe HD fan) would go crazy. The GPU also seemed to go into a degraded mode, though having a second display connected seemed to make it a bit better.

    I'd run the apple diagnostics and see what sensor it complains about.
  3. AlarmClock thread starter macrumors newbie

    Nov 6, 2014
    I assumed it was the CPU fan, as the noise comes from the bottom left corner of my iMac.

    I ran the Apple Hardware Test and it came back with the following error:

    4SNS/1/C0000008: TA0P--124

    which, according to the internet, indicates that the temperature sensor is either faulty or the installed drive (I suppose my SSD) doesn't have the required sensor, although the latter may not be relevant since I removed the SSD (but not the SATA cable) and the fan still ran loudly on boot.

    I'm currently running the extended diagnostics, which will take a while. I'll report back if it gives an additional errors.
  4. omvs macrumors 6502

    May 15, 2011
    Good - your LCD temp sensors are fine then. TA0P is the ambient temperature sensor.

    Maybe when you put the unit back together the connector for that sensor wasn't plugged back in (or connection wasn't snug?). I *think* it is one of the connectors in center area -- I had to reseat mine last week before I sold the machine, but cant remember exactly which one it was, and didn't see a great image on the web.
  5. zone23 macrumors 68000

    May 10, 2012
    On my 2011 it wasn't the CPU fan it was the HDD fan. Ya go figure the HDD has a fan? The stock HDD has a heat sensor built in or some none sense and the new HDD doesn't. I have the same year and same HDD as you. I use this app and problem solved.


    I am surprised that connecting the stock HDD didn't fix it. Give the trial a shot and see if it shutdown the fan.
  6. omvs macrumors 6502

    May 15, 2011
    I wouldn't force the fan speed - won't necessarily fix the GPU performance, and the sensor fix (which would) is probably easy.

    Though if you do want to force fans (goose it a bit for games, or other usages), I'd recommend this one instead - works under both OSX & Windows, and pretty decent functionality.

  7. AlarmClock, Nov 7, 2014
    Last edited: Nov 7, 2014

    AlarmClock thread starter macrumors newbie

    Nov 6, 2014
    I tried HDD Fan Control to no avail (it wasn't actually my HDD fan that was spinning), but Macs Fan Control worked like a charm!

    I now have the fans running around 1000rpm, give or take a hundred, and it's incredible. My typing sounds extremely, annoyingly loud. I am sane again. Hats off to you, good sir. I would name my firstborn omvs if I could but pronounce it.

    As excited as I am to have peace and quiet at my workstation, I'm only treating the symptoms at this point, and I'd like to get at the root of the problem. Also, my graphics are still stuttery, so there's that.

    As it turns out, Macs Fan Control and iStat Menus both indicate that my CPU fan and my ODD fan were both running at just under 4000 RPM. I just couldn't hear my ODD fan because the CPU fan is louder and more prominent.

    Additionally, my system animations and graphics seem to be a tad smoother (unsure why) and I was able to play Call of Duty 4 at a reasonable (but far from smooth) framerate. Minecraft, however, still shows 18 FPS, which has been the case ever since the issue began.

    TL;DR summary:

    CPU and ODD fan are inclined to run at nearly 4000 RPM. Patched but not fixed with Macs Fan Control.

    Graphics are still laggy, although they seem to be a tad smoother for some unknown reason.
  8. Dopeyman macrumors 6502a

    Sep 5, 2005
    Los Angeles!
    First question, did you just install the drive or did you replace the original drive?
  9. AlarmClock thread starter macrumors newbie

    Nov 6, 2014
    I installed it as a new drive with a separate SATA cable. The original HDD is still intact and running Mavericks, but I really only use it for storage. However, the HDD hasn't been digitally wiped or physically altered. I added the SSD alongside it.
  10. Dopeyman macrumors 6502a

    Sep 5, 2005
    Los Angeles!
    Oh, ok. I thought you replaced the original drive. If that were the case, you would need a special cable that can be obtained from OWC. I had to do that to my '11 iMac.

    Looks like you already tried unplugging the SSD and same results.

    Maybe the original drive is failing? Or try defragging the original drive first.
  11. jbuk1 macrumors member

    Oct 24, 2014
    Check none of the sensors have come loose. When I replaced my SuperDrive with a hd I didn't reattach the sensor quite right and it became loose and as it wasn't picking up any heat it did the opposite of what one might expect and threw the fans on full 'just in case'.
  12. mhafeez macrumors regular


    Oct 30, 2013
    Hi. How's your SATA connections? I mean do you use your SATA0 cable to your HDD and your SATA1 to your SSD or the other way around?

    My mid-2011 iMac is in RAID0 setup with 2 units of Samsung 840evo SSDs on SATA0 and SATA1 connection. I use HDD Fan Control to counter the fan issue and it works like a champ.

    Sorry for my bad english
  13. lakriz macrumors newbie

    Sep 12, 2013
    Im sorry to tell that your main board / logic board probably is damaged after taking it out to fit the 2. data cable :(

    I have exatly the same problem om my 3,1 2011 imac.. and haven't found a solution.

    My "solution" is to use "macs fan control" as suggested above.. and play games in windows bootcamp..

    The smc is telling OS X to slow down graphics performance to protect the system.. Windows dosnt get that information.. and therefore still have graphics acceleration.

    Macs fan control also available for windows and works perfect when i play games to control the fan speed. :)

    The only solution is a new logic board.. I have tried a new ambient temp sensor.. no luck.
    Google the fault code.. I have another old thread in this forum with two similar cases of the problem..

    I use my imac in OS X for everything else than gaming.. I haven't experienced other problems than bad game performance.. But i bought my mac 2. hand with this problem.. hoping i could fix it.. so i have never used it without the fault.

    Sorry my "danish english" :)

    /Kristian, Denmark
  14. Gav Mack, Nov 11, 2014
    Last edited: Nov 11, 2014

    Gav Mack macrumors 68020

    Gav Mack

    Jun 15, 2008
    Sagittarius A*
    When I do SSD upgrades to the imac 2011 I always go that step further and clean out the cooling system thoroughly, repaste the CPU and GPU and polish the contact plates for those dies (square on top of each chip).

    Fitting the SSD you probably dislodged some of the usual gunk dust and debris and dried up excess thermal paste dust I always find tearing them down. If you have no artefacts on the screen you are ok for now but I wouldn't wait too long.

    That sandy bridge cpu and GPU get very hot and the paste is usually dire and plates as smooth as my stubble. Shined like mirrors with chrome polish, rubbed off completely then washed with isopropyl, allowed to totally dry (unless you use denatured isopropyl like I use but that is flammable) and pasted properly (not like Apple do) they run much cooler. Make sure you clean the dies properly too


    Sorry but unless you see artefacts on the screen which suggest a broken GPU it's going to be thermal system related. I have done what I said in the previous post many times with clients and it nearly always works fine after and cooler than ever.

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