Using a "legacy" ;) 2560x1440 monitor via DisplayPort with new 27" iMac ..?

Discussion in 'iMac' started by shreddy, Jun 26, 2017.

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  1. shreddy macrumors regular

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    #1
    Hi all,

    I've just ordered a new i7 27" iMac which should arrive in a few days now.. I've been using a Dell U2711 27" 2560x1440 screen with my 13" Retina MBP (Late '13) via a miniDP(Thunderbolt 2) to DP cable. Now I'd quite like to use this screen with the iMac also - how can I do that?

    The USB-C to T'bolt 2 adapters don't support DP:
    So looks like that's NOT an option..

    I've just tried connecting the MBP to the screen via HDMI but out of the box Sierra is running it at 1920x1080. I can get it to full resolution via SwitchResX but it's blurry as hell for some reason - not sure if this is due to the 2013 13" MBP or the U2711 doesn't like it - but I figure it'd either just work or not..

    The only 2017 iMac compatible adapter is a VGA one (!) according to this page

    So not sure what to do here - looks like limited support for external monitors? Or is my U2711 just out of date re HMDI support?!
     
  2. Chancha macrumors 6502a

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    Mar 19, 2014
    #2
    The specific dongle you need is USB-C to DisplayPort. Apple for some reasons is not making and selling one themselves.

    I am in a similar situation, ordered a 2017 27", waiting for it to arrive to sit along side with my Dell UP2716D which had been in use with MBP2015 via TB2/mDP. I will get the Apple TB3 to TB2 adaptor, since I actually got TB1/2 HDDs in the chain, before the monitor (so the mDP cable from the Dell plugs into the very last chained HDD's TB port). I am unsure if the display will work on the new iMac using the same chain, only if it doesn't work then I will get a USB-C DP adaptor.
     
  3. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #3
    As mentioned, this apparently will not work. No DisplayPort support.
     
  4. shreddy thread starter macrumors regular

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    #4
    So you're saying the lack of DisplayPort support is an iMac problem then?

    Just found this cable:
    ..and it claims:
    • Compatible with 2017 iMac/iMac Pro, 2017 MacBook/MacBook Pro, Retina MacBook 12" 2015 / 2016, Late 2016 MacBook Pro, Chromebook Pixel 2015, Dell XPS 13 & 15 (6th gen / late 2015-2016), and future laptops, tablets, & desktops which comply with the VESA "DisplayPort Alternate Mode on USB Type-C Connector Standard"
    Think I might have to give it a try!

    Next problem is that the U2711 has a single DisplayPort so if I want both machines connected I'll need to shell out for an Apple TB2/mDP -> Dual Link DVI adapter ; are there cheap alternatives for this?!
     
  5. Chancha macrumors 6502a

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    #5
    Thanks for confirming this. Hmm this means the TB3 to TB2 connector is a pretty bad purchase, for desktop use I may as well get a powered hub which includes TB2 and DisplayPort, and then add a bunch other I/Os that the new iMac lacks such as analog / digital audio input that I also need.
     
  6. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #6
    No, the problem is the Thunderbolt 3 to Thunderbolt 2 adapter from Apple does not support DisplayPort, but the USBC/TB3 port on the iMac does support DisplayPort.

    Plugable says their USBC to DisplayPort cable does work. They have a 2017 iMac for testing. It looks like they haven't tested the MBP 2017 or MB 2017 yet, because they don't have those. They are relying upon end users to test it for them.

    I don't know why they mentino iMac Pro support though, since nobody has an iMac Pro to test.
     
  7. Chancha macrumors 6502a

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    #7
    I just did a rough search and was amazed by a few states of affairs:

    1) Apple TB3 to TB2 dongle won't relay DisplayPort or HDMI signal no matter what you do
    2) no TB3 dock exists that has TB2 ports
    3) half of the TB3 docks that were announced around 2016 MBP release are actually still not available

    So for people with TB2 chains consist of displays there is almost no single port solution, except the very expensive "TB3 dock with DP and extra TB3 port > TB3to2 dongle" route, where we have like 3 choices or so.

    If I separate the TB2 and DP functions to each of the TB3 ports on the iMac then I will find it very difficult to add devices into the chain, that device most probably must have 2 ports for chaining role.
     
  8. curmudgeonette macrumors 6502

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    California
    #8
    It actually does - but only when it is encapsulated in ThunderBolt.

    If you have a TB2 chain, that means you have ThunderBolt devices. Ergo, your devices can extract the video signal.

    Example: You have a TB2 RAID array with a daisy chained Apple Cinema Display. The TB3 to TB2 dongle will work to connect the RAID array. The display will also work. What won't work is trying to run the Cinema Display directly from the dongle.
     
  9. Chancha macrumors 6502a

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    Mar 19, 2014
    #9
    Thanks for your confirmation, but if I don't get it wrong does it mean:
    - if the end of chain monitor is just regular mDP then it won't work
    - if part of the chain is a TB1 RAID it also won't work
     
  10. curmudgeonette macrumors 6502

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    #10
    Both cases should work. Once the dongle converts from TB3 to TB2, i.e. from a USB-C connector to a mini DisplayPort connector, and the signal enters a TB2 (or TB1) chip, then everything beyond that point follows the old TB1/TB2 rules.
     
  11. campyguy macrumors 68040

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    #11
    banging head against wall
    Gah!
    /head banging against wall

    No offense to anyone else posting in this thread, too much misinformation here - stop thinking about anything display-related relative to Thunderbolt 1/2. First, the port is a DisplayPort port. Second, and more-likely relevant, both TB 1 and TB 2 cables and adapters are DisplayPort 1.1 compliant while most newer displays require a minimum of DP 1.2. Apple's adapter is DP 1.1 compatible, just like every single non-TB3 Thunderbolt cable and adapter ever made.

    Stop thinking in terms of "Thunderbolt" relative to displays - the two items are completely irrelevant. Today. Now.

    Older Macs have Mini DisplayPort interface ports. Newer Macs have USB-C interface ports. Both transmit DisplayPort 1.2 data transmission. QED.

    OP, the Apple USB-C adapter you called out does support DisplayPort - v1.1. Your display requires DisplayPort 1.2. That's why you're having issues. This stuff is available in both Wikipedia and your product documentation.

    Get a certified adapter from Accell, Belkin, or StarTech. Don't waste your time with crap from Plugable or any other knock-off "specialist". Make sure the throughput is sufficient. I posted the adapter to consider in the past week, I've bought 20+ for my company and I'll let you search for my posts here. /rant
     
  12. EugW, Jun 26, 2017
    Last edited: Jun 26, 2017

    EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #12
    No, Apple says the Thunderbolt adapter won’t work when directly connected to a DisplayPort monitor. That’s the issue.

    Apple itself says the adapter does not support DisplayPort.

    https://support.apple.com/en-ca/HT207266


    The Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter doesn't support connections to these devices:



      • Apple LED Cinema Display
      • DisplayPort or mini DisplayPort displays
      • DisplayPort or mini DisplayPort adapters, such as Mini DisplayPort to HDMI or Mini DisplayPort to VGA adapters
      • MacBook (Retina, 12-inch, Early 2015) and later
     
  13. Glockworkorange macrumors regular

    Glockworkorange

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    #13
  14. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #14
    Yes, as mentioned, Plugable's USBC to Mini-DisplayPort cable has been confirmed to work already. However, to be specific, it's not a dongle. It's a cable.

    [​IMG]

    BTW, I've already confirmed (and they have too) that the Plugable USBC to HDMI dongle does not work.
     
  15. Chancha macrumors 6502a

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    #15
    This behaviour is exactly what I *assumed*, since that's how the older TB1/2 devices would do. I think my confusion largely came from the Apple TB3>TB2 dongle being reported to not work with DP at all, which isn't true "literally", but on a practical basis it kind of directly is. Anyway thanks again for the answer, this means less things to buy in preparation of my iMac shipment this weekend.
     
  16. Icestyle macrumors member

    Icestyle

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    #16
  17. MMcCraryNJ macrumors 6502

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    #17
    Am I to assume that the Apple TB3 to TB2 cable, while not working with *DisplayPort* monitors, will indeed work with *Thunderbolt* monitors? I have an LG 34UM95-P, 3440x1440 UltraWide monitor, which is indeed TB2, like the Apple Thunderbolt Display.
     
  18. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #18
    It's in the Apple support note I posted earlier, but here it is again:

    https://support.apple.com/en-ca/HT207266

    It says LG Thunderbolt displays will work, although it doesn't specify the models.
     
  19. MMcCraryNJ macrumors 6502

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    #19
    Thank you so much :)
     
  20. smbu2000 macrumors member

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    Oct 19, 2014
    #20
    Is there a reason that the usb-c to hdmi dongle doesn't work?

    I currently own a Club3d usb-c to hdmi dongle
    http://club-3d.com/index.php/produc...usb-type-c-to-hdmi-20-uhd-active-adapter.html
    and when I tried it with my 2017 27" imac nothing displayed on my 4k TV. I tried it on both usb-c ports on the imac and nothing.
    I know that the dongle works (and the hdmi cable) as when I plug it into my 2016 15" mbp it displays fine and I can use it at 3840 x 2160@60hz just fine.

    With the iMac I don't get any signal or acknowledgement that something is plugged in. (The usb-c ports works as I used my usb-c to lightning cable and my iphone was detected okay.)
     
  21. EugW macrumors 68000

    EugW

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    Jun 18, 2017
    #21
    Apple has changed something with the 2017 Macs, but I dunno what. Lots of HDMI dongles that work with the 2016 models don't work with the 2017 MBP, 2017 MB, and 2017 iMacs.

    The one I bought was Plugable branded. I confirmed it doesn't work with the 2017 MB even though they have confirmed it works with the 2015/2016, and they have confirmed with their own 2017 iMac that it doesn't work with it either. And their other customers have confirmed it doesn't work with the 2017 MBP, even though it is confirmed to work with the 2016.

    Since then, Plugable has added in their description specific mention that it is incompatible with the 2017 models (yet retains compatibility with the older models).

    However, as mentioned, the USBC to Mini-DisplayPort cable continues to work with both generations. I have since ordered a USBC to DisplayPort dongle from Monoprice to give that a shot with my Mini-DisplayPort 2010 iMac to use that as a monitor (with the appropriate DisplayPort to Mini-DisplayPort cable). However, maybe I should have gone with the Plugable since they ship a lot quicker. I'm still waiting for the Monoprice one to arrive (to Canada).
     
  22. kap28 macrumors newbie

    Joined:
    Jun 27, 2017
    #22
    Same issue here with my 2017 iMac 27" and Dell U2713HM (27", 2014, 2560x1440). See attached image for what cables/adapters I have tried.

    Could anyone confirm that this Plugable cable or HP adapter work with any Dell monitor?
     

    Attached Files:

  23. shreddy thread starter macrumors regular

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    #23
    My Plugable cable arrives today, iMac should be arriving tomorrow (hurray!) so I'll let you know how it goes with my U2711..
     
  24. Icestyle macrumors member

    Icestyle

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    Location:
    Vienna, Austria
    #24
    As i wrote earlier, it works for me with the U2715H. I see no reason why it wouldn't work with your U2713HM.
     
  25. kap28 macrumors newbie

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    Jun 27, 2017
    #25
    Any update on your situation?
     

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