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  1. #16
    Curious Cable Question
    krs's Avatar
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    Quote Originally Posted by kitjv26 View Post
    krs,

    Unfortunately, my backup drive also has Catalina installed. Neither of my other Macs have USB-C ports, so I cannot try the 2 cables on those machines. However, I did connect the external display to an older MacBook Pro with a DVI-to-DVI cable & it worked flawlessly. In fact, I could not get the display to fail. So I am reasonably confident that the display is fine.

    Since it is my understanding that not all cables are created equally, I suppose that the 2 cables I tried were not "Catalina-compatible".

    The iMac is a 27" Retina 5K 2017. The external display is an NEC MultiSync P221W.

    Regarding "resolution"...the iMac has a resolution of 5120 X 2880 retina. Looking up the specs for the NEC display (which is about 7 years old), it does not show support for the resolution of the iMac display. I do not know if that is a concern. I say that because I use the NEC display for photo post processing. I have had no issues with calibrating the display nor soft-proofing images for printing.
    It's hard to troubleshoot something by postng back and forth in a forum unless the issue is already well known.

    For instance, I thought you were talking about a Thunderbolt 1 or 2 port when I read your first post - it only rang a bell that it is Thunderbolt 3 when you mentioned a USB-C port in your last reply.
    And the 2017 iMac may also have something to do with that although you said the cable was working fine until you upgraded the macOS.

    As to the Belinda cable, is that actually a cable or an adapter?
    I looked at one Belinda USB-C to DVI adapter and it states in the description that this adapter is not compatible with a 2017 iMac.
    https://www.amazon.com/Belinda-Adapt.../dp/B073S81DK5

    What is the actual cables that you have right now?

  2. #17
    Curious Cable Question
    ferrarr's Avatar
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    Why not jus get an adapter, USB-C to DVI?


    Sent from my iPad using Mac-Forums
    -- Bob --
    Please backup. Everything has a life cycle, unexpected and warning free. Nothing will last as long as you want it to.

  3. #18
    I apologize for any confusion from not being more specific. Yes, I should have specified that the port on the iMac is a USB-C.

    As for the cable, it is indeed a cable; not an adapter. The Belinda adapter you referred to is NOT what I have. I have: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1.

    - - - Updated - - -

    Quote Originally Posted by ferrarr View Post
    Why not jus get an adapter, USB-C to DVI?


    Sent from my iPad using Mac-Forums
    How would that different from using a USB-C-to-DVI cable? Also, both ends of the cable or adapter have to be male.

  4. #19
    Curious Cable Question
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    Quote Originally Posted by kitjv26 View Post
    How would that different from using a USB-C-to-DVI cable? Also, both ends of the cable or adapter have to be male.
    There is no difference if it's from the same manufacturer.
    For your application, a cable is the better way to go.

    However, in the description of the cable you posted, there is the same comment about incompatibility with a 2017 iMac
    compatible with with the 2015/16 MacBook, 2016 MacBook Pro (NOT 2017 iMac or MacBook)
    I assume that is because of the chip set they use in both the cable and adapter.

    What is the second cable you have?

  5. #20
    Thank you for noting the compatibility reference. I totally missed it.

    That link that I sent to you was for the second cable, so to speak. The original cable is from the same manufacturer & looks identical. However, unlike the second cable, the original will work in an hour or so after the external display is plugged back into both the power source & the iMac.

  6. #21
    Curious Cable Question
    krs's Avatar
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    Quote Originally Posted by kitjv26 View Post
    ....... the original will work in an hour or so after the external display is plugged back into both the power source & the iMac.
    Can you explain exactly what happens step-by-step
    It sounds as if the iMac takes an hour or so to detect the external display and then it works properly???

    Did you try various combinations of the sequence when you plug the cable in vs powering up the iMac and/or powering up the monitor.
    I have not used an external display on a Mac for a long time, but I remember years ago when I did, I had to power up and plug in the cable to the monitor in a specific sequence.

  7. #22
    Curious Cable Question
    MacInWin's Avatar
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    Just one comment for kitjv26. Just because it looks like "just a cable" does not mean there is no embedded chip in the connector. It could be that either there is no chip, and the system expects one, or there is a chip, but it's incompatible. More and more cables these days are "intelligent" cables rather than just a length of conductor.
    Jake

  8. #23
    Quote Originally Posted by MacInWin View Post
    Just one comment for kitjv26. Just because it looks like "just a cable" does not mean there is no embedded chip in the connector. It could be that either there is no chip, and the system expects one, or there is a chip, but it's incompatible. More and more cables these days are "intelligent" cables rather than just a length of conductor.
    Yes, that is something that I have learned since dealing with this issue.

  9. #24
    Quote Originally Posted by krs View Post
    Can you explain exactly what happens step-by-step
    It sounds as if the iMac takes an hour or so to detect the external display and then it works properly???

    Did you try various combinations of the sequence when you plug the cable in vs powering up the iMac and/or powering up the monitor.
    I have not used an external display on a Mac for a long time, but I remember years ago when I did, I had to power up and plug in the cable to the monitor in a specific sequence.
    Here is a compendious run-down of this issue. I had used the NEC external display with my iMac (and the same cable) since 2017. Never a problem. Immediately after upgrading to Catalina, the iMac restarted & the external display went "black" as if it was not detected. I tried a variety of steps including: resetting the NVRAM & the SMC, power cycling the iMac, as well as the external display. Having no success bringing the display back to life, I went to bed that evening. The next morning I awoke the iMac from sleep & to my surprise the external display was up & running.

    All was fine until I had to restart the iMac for some reason or other & the external display again went black. Some experimentation indicated that if I unplugged the external display from both the power source & the iMac and then re-plugged them, within an hour the display would be up & running again. As long as I do not restart the iMac or disconnect the display cable from the USB-C port on the iMac, the display works fine. If I simply unplug the display from the power source (but leave the cable connected to the iMac), the display will reboot; no problem.

    As a side note, when the display is functioning perfectly & I navigate to Apple Menu > About This Mac > System Report > Thunderbolt, on both USB-C ports ("no device is detected".

    That's pretty much it. I hope there is some glimmer of insight in my explanation. Thank you kindly!

  10. #25
    Curious Cable Question
    MacInWin's Avatar
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    What is in System Preferences/Dispays? When you get there, does a separate box open on both the iMac and the external? on the Arrangement tab, do you see both displays?
    Jake

  11. #26
    Curious Cable Question
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    Quote Originally Posted by kitjv26 View Post
    ..........when the display is functioning perfectly & I navigate to Apple Menu > About This Mac > System Report > Thunderbolt, on both USB-C ports ("no device is detected".
    What does it show if you look under Apple Menu > About This Mac > System Report > Graphics/Displays?

  12. #27
    Curious Cable Question
    krs's Avatar
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    @kitjv26 - Can you post a link to the cable you are using now - the original one.

    Looks like other people have pretty much the same problem that you have, for instance:
    Has anyone gotten this cable to work with macos catalina?
    Answer:This worked great on Mojave, when upgraded to Catalina it rarely detects the monitor when I first start up - but with no changes it will often 'appear' later in the day. Does not make any sense at all. Turning off/on restarting reset NVRAM/SMC etc does not seem to have any real effect. Don't think it's a cable issue, as when it's working it works great.
    Sounds to me that the problem is related to a marginal digital signal level.
    I don't think there is a "fix" with the components you have now.
    Either live with the present situation, ie wait a long time after rebooting the iMac, or try to find a cable from another supplier with a different chip set and where reviews and comments indicate that the cable will work with a 2017 iMac and Catalina and (ideally) with your monitor.

    PS: You could also try flipping the cable around at the USB-C connector end to see if that makes any difference.
    The USB-C connector is supposed to be symmetrical but that is only true if it is wired correctly. Honestly - I doubt that will make any difference - the long delay that you encounter before the monitor shows an image indicates that the iMac and monitor can't communicate initially which points back to a digital signal level issue.
    Last edited by krs; 11-16-2019 at 01:02 PM.

  13. #28
    Curious Cable Question
    chscag's Avatar
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    Sounds more like another Catalina bug that Apple needs to squash. Sorry, but the more I read about the bugs and problems folks are having with Catalina the more it reminds me of two infamous operating systems from Microsoft: WinME and Vista. Anyone remember those?

  14. #29
    Curious Cable Question
    MacInWin's Avatar
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    Sorry, but the more I read about the bugs and problems folks are having with Catalina the more it reminds me of two infamous operating systems from Microsoft: WinME and Vista. Anyone remember those?
    Charlie, I don't think Catalina is anywhere near that bad. I'm running it just fine on a mid-2015 15" MBPr with a Thunderbolt external display, eleven external drives, two printers and a Thunderbolt hub. Zero issues. I think there are more complaints about Catalina because of the huge shift in how it is installed and the abandonment of 32-bit software. I'm also wondering if the 32-bit impacts older intelligent cables? Going forward, if the tech companies continue putting intelligence in cables it's going make us all more careful about what we buy and where we buy it.
    Jake

  15. #30
    Curious Cable Question
    chscag's Avatar
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    Hey Jake:

    There's always a success story in every endeavor. Must be all that good living.

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