2017 27" iMac and External Monitor not working

Discussion in 'iMac' started by ks-man, Oct 10, 2017.

  1. ks-man macrumors 6502a

    Sep 25, 2007
  2. Precursor macrumors 6502a


    Sep 29, 2015
  3. theluggage macrumors 68040

    Jul 29, 2011
    Should "just work".

    There seems to be a problem with some adapters and the 2017 MacBook Pro and iMac. There are a couple of reviews for yours saying that it doesn't work with the 2017 MacBook Pro.

    Its a bit too late now, but I'd recommend picking one that explicitly says "compatible with 2017 Macs" in the product description.

    Here's the one I use (and lots of people have posted on MR saying it works):


    If you want further conformation, though, it would help if you said what monitor you were using.

    Isn't USB-C wonderful...?
  4. Fishrrman macrumors P6


    Feb 20, 2009
    the luggage wrote:
    "Isn't USB-C wonderful...?"

    Yep. All it was cracked up to be, right?

    The advice about the cable in reply 3 above is dead-on.
    You probably just need another cable that is "known to work" with USB-c and a 2017 Mac...
  5. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    It's a piece of junk? The ad states "compatible" and not "complies with" or "compliant" and the ad also leaves out DisplayPort and VESA. I stick with brands that go through DisplayPort's certification - $30-ish for a Belkin or Accell cable, several in my offices, all work perfected with iMacs and PCs. My 2¢.
  6. theluggage macrumors 68040

    Jul 29, 2011
    Would that be this Accell cable:


    ...with half-a-dozen 1-star reviews on Amazon specifically saying that it doesn't work with the 2017 MBP (which is likely the same issue affecting 2017 iMacs)...?

    I can't find a USB-C to DP cable on the Belkin site.

    For the avoidance of doubt: there appears to be an issue specific to 2017 MBP and iMac models that is incompatible with some USB-C-to-DP cables. Regardless of whether it is the Mac or the cable that isn't compliant only buy USB-C to DP cables that have been confirmed to work with 2017 Macs.

    The Plugable cable is one that multiple people on Macrumors have confirmed to work, and the manufacturer's website specifically lists compatibility with the 2017 MBP and iMac. If anybody knows a better option that they have actually used with a 2017 iMac or MBP then do share.
  7. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    I did write iMacs - no other iMacs have a USB-C port. I did not write 2017 rMBPs, and there aren't any 2017 rMBPs in my offices so I have no experience with this combo. I was very clear - shall I use bold text next time? Do what you want…

    BTW, that link to Amazon - all of those 1-star reviews were for the "USB-C to HDMI 2.0 Adapter". :rolleyes:
  8. imaccooper macrumors 6502


    May 29, 2014
    North Carolina
  9. theluggage macrumors 68040

    Jul 29, 2011
    Whups. Apologies - Amazon caught me out there by lumping all the reviews together.

    Interestingly, Looking more closely at the photo, the plug mouldings on the Accell cable look identical to the Plugable one (including the 'waist' on the DP body), and the StarTech one, too (and clearly different to the one the thread starter bought) so odds are we're talking about the same Chinese cable...
  10. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    No worries, I'm never serious about this stuff, life's too short! :D

    I'd done a bunch of electrical tests some time ago (listed in the looooooonnnggg Dell P2415Q/P2715Q thread), and some follow up since then. Apple's apparently done some cracking down on spec compliance, especially VESA and DisplayPort, with Sierra and beyond. I have dozens of engineers and tech working for me - some Mac/PC and display combinations worked 100% of the time and some didn't, and my company bills out a bunch of $$$ every hour so I wanted to get to the bottom of what was going on. Lots of my posts are here in these forums about this. Ugh.

    Cutting to it, Accell/StarTech/Belkin/Eizo spend their money to make sure their cables comply with VESA/DisplayPort. Plugable, COXOC, and the company you cited do not. A key is that I found 100% of the cables that weren't on the DP products portal (around 100 cables) returned power over Pin 20, which can and often does interfere with the display and computer conveying DisplayID information to each other. I was pretty grumpy at the end of that long weekend, spent with my multi-tester and not my GF, but now I've got 100% uptime in my offices going back 18 months. I cited my reference to a post on [H]ard|Forums, and nothing has changed.

    Compliant cables have Pin 20 physically blocked, "compatible" cables that I've tested never have Pin 20 physically blocked. Yes, this is a thing. The ends and pin configuration look identical, but the cable "innards" are not identical. Plugable is a reputable company only among people that don't know any better, they just don't take the time to get their products right - last time I checked none of their DP-related products were VESA/DP certified, and the last time I subjected them to my own testing they all pushed power over Pin 20, not a good thing.

    Also, Belkin/StarTech/Accell also offer 2-year warranties as does Eizo. Eizo is the only display maker that included compliant cables with their displays. Belkin/StarTech/Accell cables are made in China, Eizo cables are all from Japan; I haven't checked the Iiyama displays we have.

    Honestly, no, they're not the same cable assembly. My Dell 4k displays shipped with sh** COXOC cables, and those cables are all in a landfill somewhere.
  11. ks-man thread starter macrumors 6502a

    Sep 25, 2007
    Thanks for the responses. I will try getting the cable in post #3. The one I have says Avotch. The monitor is a Dell 2815Qf.
  12. theluggage macrumors 68040

    Jul 29, 2011
    I'm not plugging Pluggable as a company (although their website is amongst the most helpful in terms of listing compatibility) - I just know that their USB-C to DP works for me (and other MR users).

    Where do you go to check DisplayPort compliance? I've looked on:


    ...and that doesn't include any USB-C to DisplayPort cables from anyone.

    Nor can I find any USB-C to DP cable from Belkin...
  13. campyguy macrumors 68040

    Mar 21, 2014
    Portland / Seattle
    VESA and USB-IF are working on a published certification program. That portal contains only DP-relevant items, but the site also contains plenty of USB-C-relevant information (read on…).

    Currently, if a cable (or other USB-C device) is certified by USB-IF for use with video applications, it's compliant with VESA/DP requirements and is certified to carry the USB-IF logo and also the DP logo. Certified is my key word; DP posted an article on its web site that VESA bought and tested hundreds of not-certified (read:"compatible") cables and adapters (2015/6) and 100% of them failed - all of the cables in my offices that weren't certified by VESA/DP failed, and that's the lesson I learned last year. I've come to trust that, if a brand is on the DP products portal for the intended purpose I need I'll give it a try. My company must have not been able to bill (read: lost) maybe $25k with freezing/sleeping/rebooting computers in FY 2015 and 2016 because of sh** cables and lost productivity.

    Plugable has had two products on that DP portal, both for HDMI-related cabling. Not interested. More relevant - here's my rationale, Plugable is aware of the certification program, but they've chosen to not certify their other products. That, to me, is a damning element in getting me to not consider their products.

    I called Accell and Belkin and they've submitted their products to USB-IF for evaluation, and the boxes of the recent products I've purchased carry the USB-IF certification logo. The track record of those two companies - and that of both Eizo and StarTech for cabling, and both Eizo and BenQ for displays (I own about a dozen of each) - in the VESA certification program is good enough for me right now. I still break out my multitester now that I know what to look for.

    https://www.displayport.org/faq/ (skip to "How will I know if the Type-C connector on my device supports DisplayPort over USB-C?")

    My main focus is waiting until more DP 1.4-certified products ship. Also, look for throughput only for 2160p or greater - you'd be surprised how many "4k" cables are 1440p- or 1600p-rated. My 2¢. Cheers.

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12 October 10, 2017