Two External Monitors on a 2013 Slim iMac

Discussion in 'iMac' started by Steve11, Jul 25, 2013.

  1. Steve11 macrumors newbie

    Jul 25, 2013
    Is it possible to connect two external monitors to a 2013 Slim iMac? I've got two ThunderBolt Ports. I picked up two thunderbolt to DVI cables (not adapters). I've tried using a TB to VGA and a TB to DVI to no avail, and also a TB to VGA and a TB to VGA and I can only get one monitor working at a time. It comes down to whichever one is plugged in first. On a side note this occurs in Mountain Lion as well as Mavericks, I'm back at Mountain Lion on this machine now.

    How do I get this to work?
  2. TyPod macrumors 68000


    Nov 2, 2006
    And Yourself?
    What resolutions are you trying to power on the external displays? It could be possible that they are too high.
  3. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    How do you have a 2013 iMac, the latest available to the general public is the late 2012 model.

    What Thunderbolt to DVI cable are you using? In theory the iMac supports 2 external displays. Have you tried Apple's Mini DisplayPort to DVI Adapters? Also When you tried are you plugging one into each thunderbolt port? Or or you somehow trying to daisy chain them off the same port? It should be one per port.
  4. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    It probably is a late 2012, I just got it a couple weeks ago. I have tried the apple to DVI Adapters, as I said in my first post. I'm plugging one adapter into each thunderbolt port. As far as the monitor, should I somehow change the resolution within the settings on the monitor, because no matter what I change it to on the iMac in Display Preferences, it makes no difference at all.
  5. 432521 macrumors newbie

    Aug 10, 2010
    I have the lowest model 21.5 and I have two monitors attached so you can get 3 total inputs from any late 2012 iMac.

    My setup is one mini display port to hdmi converter connected to my samsung TV and one mini display port to dvi-d to my ASUS monitor.
  6. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    well this is completely nuts then. I wonder why it won't work. I have identical monitors, identical cables and everything. I'll try to go into the setup menu on the actual monitors and see if I can dial anything down there. If I set the resolution from within the Display Preferences it only shows the one monitor and won't work.

    Another thing to reiterate, this is a 21.5" iMac, and I have never seen anything definitive about whether or not two displays connected is possible, I have however seen alot of information on 27" iMac's being absolutely possible. Not sure if that is the issue here or not.
  7. FreakinEurekan macrumors 68040


    Sep 8, 2011
    Eureka Springs, Arkansas
    Good question. According to the tech specs:

    This implies one external display is supported.

    I know some people have dual externals working on 27" but of course the GPU is different on the 27" so that may be the reason.
  8. 432521 macrumors newbie

    Aug 10, 2010
    like i said my imac is also a 21.5 inch, I bought it about 2 weeks ago so it is the newest model out there (late 2012) and I have 3 total screens going (2 external and my iMac screen) going and they all work perfectly fine.
  9. boy-better-know macrumors 65816


    Jun 30, 2010
    Have you tried connecting both monitors and then restarting your iMac?
    I was having trouble with my late 2012 27" iMac with one external display until I restarted it. The iMac recognised the monitor on startup and all was well.
  10. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    Yep, tried it several times. Nothing seems to work. I am going to mess with it again as I get time.
  11. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    I just went back to the two Apple Thunderbolt to VGA connectors and tried it connected to two identical AOC 2050S WD monitors. I also had the two monitors connected with two DVI to Thunderbolt cables like these. Nothing works. I tried taking the display resolution down on each monitor to 800x600 even and still nothing. Rebooting even after each change. Only one monitor at a time. This configuration also now has a fresh and updated installation of Mountain Lion on it.

    AND I just hooked up an ASUS VE228 monitor along with my AOC monitor both connected with a TB to VGA adapter. And just for kicks I put an HDMI to DVI adapter at the monitor side of the ASUS, connected a DVI cable to it and ran it to a DVI to TB adapter at the iMac, the same situation occurs. And with a reboot, the HDMI connected monitor won't even display anything at all. without reseating the TB connection...

    I have to say, I absolutely love Apple. I have been a Windows user since it first came out. I'm now a Network/Systems Admin for a total Apple Network for about 18 months. This is one thing that has really driven me insane is the inability for me to have multiple displays. I finally get an iMac with two Display Ports and it won't work. I have an Apple Rep but he doesn't know whether it is even possible or not. I could really use this feature. It would free up a computer for someone else as I need two monitors to work, and one more computer just to remote desktop into Servers, one of which I need up all the time that monitors all of my Network using a program called Intermapper.
  12. DennisD7 macrumors member

    Jul 17, 2012
    London, UK
    I just want to confirm that two external monitors do indeed work, at least for me. I have two dell 20-inch non-widescreen 1600x1200 each. I use the same type of cable you link to, and it was no trouble setting it up. I think there is something with that resolution though, that it's just under the Dual link DVI limit somehow, but I haven't investigated that closely.
  13. chabig macrumors 601

    Sep 6, 2002
    And yet you purchased a machine that according to specs only supports one external display.

    The number of Thunderbolt ports has no bearing to the number of supported displays. TB is a high-speed digital interface. It's ability to support displays may be limited by the GPU of the machine. You have to read the specs to find out.

    Coming from Windows, you've become accustomed to working around Windows limitations. That's why you think you require to displays for work. Mac OS is much better at window management than Windows, with Mission Control and Spaces. You said you've tried Mavericks on the machine. With Mavericks you have have Intermapper displayed full time on the external while you work with Spaces on the main display.

    The fact that some people have found two displays to work is probably an anomaly. One said he used TB to HDMI adapters. You haven't mentioned trying that.
  14. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    I've actually purchased 12 of them this year, and 7 MacBook Pros, AND 170 MacBook Airs, 50 iPad Mini's, 3 MacMini Mountain Lion Servers, along with some Gigabit switches, and a host of other things. If you are looking to troll, go elsewhere, I'm looking for help getting two monitors up and going. It is really something that I want to do just so that I can free up a computer, if it doesn't work out, I suppose I'll just have two iMacs each with another display and I can remote into the other one, not the end of the world. Don't act like I made a decision to purchase something based on misinformation. That is definitely not the case.

    And as far as working around the limitations of Windows machines, while I absolutely like working with Mac way more than Windows, any day, for countless reasons, Windows ability to have SEVERAL external displays definitely outshines what I am going through here. I even have a Mac Representative that I can go to for help, and he isn't even sure it is possible. And from reading around, it is possible, proven by some of the posts here. I'll keep on beating on this, I'm sure it can work, and as far as an anomaly, we are talking about Apple here, I doubt that they have many of those.
  15. Maxx Power macrumors 6502a

    Maxx Power

    Apr 29, 2003
    From what one of the posters said about the 2 monitors working at 1600x1200, I think what is happening is that there is only 1 stream of DVI-D, dual link. So the most you can get is split it up to 2 streams of DVI-D, single link. Then, the 2 external monitors you attach can not have more resolution than a single link can support (and I think about 1080p/1200p is the upper max), then it should work. Just an observation from those who apparently can get it to work...

    If not, the next thing to check is the cable length and quality, I suppose.

    I am not CERTAIN if this is the cause.
  16. chabig macrumors 601

    Sep 6, 2002
    Mac OS supported multiple displays way before Windows, and does a better job of it, in my opinion. Your issue is not with Mac OS. It's with your specific machine, which doesn't have hardware support for more than one external display.
  17. Steve11 thread starter macrumors newbie

    Jul 25, 2013
    You are certain of that? Seems to me like it does as others have it working. If not then I can't see how they have it up and running. And if it does, what are the parameters? What is the threshold?
  18. 432521 macrumors newbie

    Aug 10, 2010
    have you tried hooking one monitor up with a dvi-d and one up with an hdmi capable monitor or tv?
  19. Outrigger macrumors 68000


    Dec 22, 2008
    How can his machine not be capable of support 2 externals when he has the latest iMac? His machine has 2 TB ports.
  20. chabig macrumors 601

    Sep 6, 2002
    Thunderbolt ports are high speed serial data ports, not display ports. The number of ports does not correlate directly to the number of supported displays. It also works the other way around--for example, my MacBook Air has only one Thunderbolt port but I can have more than one external drive connected to it.
  21. NorCalLights macrumors 6502a

    Apr 24, 2006
    OP: Have you tried exactly what is listed here? I'd be curious if there's something magical about the combo of 1 MDP to HDMI and 1 MDP to DVI-D adaptor.

    Failing all of the suggestions here, you could always get a Matrox DualHead2Go box and connect two external displays that way. They even make one with 1xDisplayPort in and 2xDVI-D out.

    Good luck... not sure why it would work for one machine, but not on an identical machine.
  22. aggri1, Aug 1, 2013
    Last edited: Aug 1, 2013

    aggri1 macrumors 6502

    Jul 21, 2010

    my 27" 2010 wouldn't recognise an external display recently. Then I did a PRAM reset, and voila, came straight up. That old chestnut.

    Hold down COMMAND and OPTION and P and R as soon as you press the power button to start it up. Hold those four keys down until you hear it restart. You might like to hold them down until it restarts a second time, sometimes you'll hear people say that. I'm not sure whether that does anything extra.

    Anyway, I've no idea whether this may cause your symptoms (or indeed, resolve them), but it's a harmless little trick. I can't remember whether this resets the time on the newer Macs or not.


    EDIT: can anyone inform us one way or another whether that also works with those dicky little wireless keyboards?
  23. MeFromHere macrumors 6502

    Oct 11, 2012
    The system supports two external thunderbolt displays:

    But I haven't found anything that says it supports two external DVI displays.

    Exactly what TB to DVI cables are you using? Are you sure they are really TB to DVI, or are they actually Mini DisplayPort to DVI?
  24. Outrigger macrumors 68000


    Dec 22, 2008
    I don't think you got what I said. First, TB ports are not serial ports, they're pci-e. Second, I didn't say the number of ports correlate to the number of external displays. The OP stated he has the latest iMac which DOES support 2 external displays, and that was my point.
  25. chabig macrumors 601

    Sep 6, 2002
    Pci is serial.

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