Mid 2011 27" iMac and two thunderbolt displays.. Anyone running?

Discussion in 'Mac Accessories' started by Ccrew, Dec 30, 2013.

  1. Ccrew macrumors 68020

    Feb 28, 2011
    Have this setup giving me fits and wondered if anyone else is experiencing the same issue. And how to best troubleshoot it. Apple says it's supported.

    Here's what I've tried so far:
    Display to each thunderbolt port on the iMac: Right display doesn't work

    Right display to iMac with crossover thunderbolt cable to left display: Neither external monitor works

    Left display to iMac with crossover from left display to right display - Both monitors work.. UNTIL machine sleeps at which time right monitor won't wake until iMac is cold booted. Warm boot display stays dead.

    All parts, cables, etc are Apple, so no third party silliness. All firmware latest, either monitor using it as a single works fine, or using it as a single external to the iMac works fine also. Appears to be tied to the dual setup related to the right monitor.

    What I can't find clear docs for though are whether I should be able to plug each of the Thunderbolts to each of the 2 iMac Thunderbolt ports and have them work (It doesn't). It looks like it's supposed to?

    Best I've found is @ http://support.apple.com/kb/ht5219#18

    Where it says "iMac (27-inch, Mid 2011), iMac (21.5-inch, Late 2012), and iMac (27-inch, Late 2012) with two Thunderbolt ports supports a total of two Thunderbolt displays regardless of which Thunderbolt port each display is connected to"

    Either monitor hooked to something like my Mini or my MBP work just fine as a single monitor.
    Ideas appreciated.
  2. DeltaMac macrumors G3


    Jul 30, 2003
    Can you decide whether just one monitor affects everything?
    By that, I mean is it always the same display that exhibits the problem? It WON'T be the "right" one, as your hardware doesn't know which display is on the right. That's determined through software. For example, there's no TB port labeled "right", or "left"

    Article with more info: http://support.apple.com/kb/PH13814

    As your post is a little confusing (your Mac doesn't know which display is right or left, only you know), I suggest that you identify each display in some physical way, like a different number sticker on each - so as you move them around, you know which display you may have problems with.
    My suggestion for a test:
    Connect display A to the iMac TB port. Connect display B to display A port. Use until you see problems, and note which display has issues (or both?)
    Then swap: display B to iMac, and display A to display B port. Is there any difference with which display has problems, or still on both?
    Finally, display A to iMac, and display B to iMac.
    Decide which display gives problems, then swap A and B on the iMac ports. See if the issue stays with one display, OR, if it is either display, whichever display is plugged in to a certain port.
  3. Ccrew thread starter macrumors 68020

    Feb 28, 2011
    Thanks. Problem seems to stay with the display.. Almost like it will be an endpoint but won't do passthrough?

    But even as an endpoint when it does work, it won't wake from sleep unless it's initialized via a cold boot.

    Make more sense? Yeah, I realize that the machine doesn't know right from left (actually it does, but only in display preferences) but electrically it apears the monitor only works when on the end of the thunderbolt bus?

    Interesting though in your link the way I read it I shouldn't need the crossover thunderbolt cable, and should only need to hook each display to each of the two thunderbolt connectors on the iMac? If that's the case it's NOT a passthrough issue, as only one external works that way.
  4. DeltaMac macrumors G3


    Jul 30, 2003
    I have to ask:
    What do you mean by "crossover cable"?
    I've not ever heard that term used with thunderbolt.
    Do you have a home-made cable of some kind?
  5. Ccrew thread starter macrumors 68020

    Feb 28, 2011
    No. Since the monitors won't work with each plugged into the iMac.. I'm plugging the built in Thunderbolt connector off of one of the monitors (the cable with the magsafe paired to it - and this is the "left" monitor) to the iMac, then from the other thunderbolt port on that (left) connected monitor running an Apple thunderbolt cable from that monitor to the female TB port on the second monitor (right monitor). But this is the ONLY way both work, albeit has the sleep issue.

    If I reverse it and feed the right first then crossover to the left it doesn't work.

    Think of it as a long chain which by Thunderbolt standards technically should work, in that I feed the left monitor, passthrough, then feed the right. And like I said in the original post, there are no third party hacks here, everything including the cable are all genuine Apple.

    Also these are 2nd generation TB monitors that have 2 thunderbolt connections (one cabled, one female), so they're not like first gen where they had to be on end of chain.
  6. Brian Y macrumors 68040

    Oct 21, 2012
    On a similar note - I think the 2011 iMacs are fussy when using 3 displays.

    My setup is the internal 27", plus a 24" Dell ultrasharp, (1920x1200) and I have it hooked up to my TV too. When the Dell is connected, I can only run the TV at 1080i, 1080p just gets a black picture. Unplug the Dell, and I can run it at 1080p no problem :p.

    It's not really a problem, I only use it to put Spotify on, but I thought it was an oddity.
  7. Ccrew thread starter macrumors 68020

    Feb 28, 2011
    Yeah, I'll add to this..

    I was running two TB to DVI adapters driving twin Samsung 25" monitors before I repurposed my TB monitors and they worked perfectly. Go figure that a pure Apple solution is problematic!! :(

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