2011 iMac 3rd Display Flickering?

Discussion in 'iMac' started by gbarlow, May 14, 2011.

  1. gbarlow, May 14, 2011
    Last edited: May 14, 2011

    gbarlow macrumors newbie

    May 28, 2010
    Ottawa, ON
    Hey there! Hoping everyone here might be able to help me figure out what's going on with the setup.

    2011 27" iMac
    3.4ghz i7
    12GB 1333MHz DDR3 RAM
    1TB ATA Drive
    AMD Radeon HD 6970M 2GB

    2 X 24" ACD

    When the two external displays are setup with the iMac one of the screens flickers / distorts every few seconds. The displays individually are fine, and both work perfectly on their own, or connected to a MBP. However once they are both connected to the iMac one get messed up...

    Driving all 3 at native right now, dropping the resolution hasn't made any difference though.

    I've narrowed it down to one of the TB ports, however am not sure if its an issue with the port itself or trying to drive too much screen real estate? Has anyone else tried 3 displays yet?

    Any thoughts?
  2. shyum2 macrumors newbie

    Jun 1, 2011

    I have the same issue. When I plug in my 24" cinema display into my iMac, it flickers every so often. When I plug it into the other thunderbolt port, it works fine. When I plug it into my notebooks, it works fine as well.

    Any idea what's up with this? As it seems that one port is having issues, the other port is okay.

    My iMac is the same as yours.

  3. gcthompson macrumors newbie

    Apr 6, 2010
    I've got 3 displays on my 2011 27" iMac (the base model with 512Mb VRAM)

    Seems to work fine though my resolutions are probably lower

    1680 x 1050 for one of them
    1920 x 1080 for the other

    Both are plugged into the thunderbolt ports using DVI adaptors

    That said, one of them always comes on slightly later than the other but both displays are stable for me...
  4. d1sahib macrumors newbie

    Oct 17, 2009
    Reston, VA
    I have the 3.4GHz 27" iMac with 2GB of video RAM, and have connected a second display (24" Apple LED) to it. I am getting periodic flickering/blanking on the 24" (the iMac display is fine) and this is happening regardless of which thunderbolt port I use. The 24" is fine when connected to a Mini or the Air so I know the problem is not with the display.

    In the meanwhile, I have put in a support request, and should have more on this by the end of the day.
  5. jonnodotsg macrumors newbie

    Jul 3, 2011
    I am experiencing the same issue as well, both before and after having installed the recent Thunderbolt firmware upgrade.

    I find that my two external displays (1 ACD and 1 NEC 2490WUXi2) run perfectly fine with no flickering if the displays have not had a chance to go to sleep since booting up. Once they have gone to sleep once, it's over. The ACD will flicker ever so often, so I'd just reboot again.

    Anybody heard anything from Apple about this?
  6. johnfkitchen macrumors regular

    Sep 7, 2010
    I have two 1680x1050 displays connected via the two Thunderbolt ports (mini displayport to VGA). No flickering.
  7. Razorback7 macrumors newbie

    Jul 28, 2011
    I am also experiencing this problem on a 2011 27" iMac with two 24" ACD's. I have the firmware update applied.

    The flickering occurs one ONE of the monitors after a resume from energy saving mode. It is always the monitor connected to the Thunderbolt port nearest the USB ports. The problem follows the port, not the monitor (i.e. swapping monitors does not help.)

    For the sake for experiment, if I replace the ACD with with an HP 24" monitor using a mini DisplayPort to DisplayPort cable, the problem does not occur. It seems like it is something to do with that particular TB port and an ACD monitor.
  8. jvmxtra macrumors 65816


    Sep 21, 2010
    SO sick of this flickering issue. We should not have to deal w/ this after spending this much money. WTF apple???
  9. Stan Mikulenka macrumors 6502

    Nov 20, 2009
    Calgary, Canada
    you guys have a mobile vid. cards...
    Do you REALLY expect it to run 3 monitors flawlessly?
  10. xraydoc macrumors 604


    Oct 9, 2005
    I've read other reports of the 24" LED Cinema flickering or otherwise behaving oddly on TB-enabled Macs.

    Sounds like it'll either be unfixable or Apple will have to release some firmware updates.
  11. Mord macrumors G4


    Aug 24, 2003
    If it's specced to do something it should do it, it doesn't say "supports two external monintors over thunderbolt, but one will flicker a bit" does it?
  12. logics8 macrumors member

    Oct 14, 2008
    Graphics issues.

    I have the 1gb version of the 6970 in my 27 inch iMac and I've been getting screen flickering and distorted images too. I've narrowed it down to overheating but I'm in contact with apple over it.

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