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USB-C 4K monitor through a Caldigit Thunderbolt 3 dock problem SF314-59

I have a setup with my Macbook using a Caldigit Thunderbolt 3 dock, which drives 2 displays, 1 through USB-C and one through a display port.  Works great.  When I plug in the Acer Swift 3 into the dock, everything on the dock works the same except for the USB-C 4K Dell monitor not getting a signal.  I can bypass the problem using HDMI from the laptop to the display, but I can't figure out why the USB-C connection doesn't work with the Acer when it works with the Macbook.  Any ideas?

FAQ & Answers

  • billseybillsey ACE Posts: 20,565 Trailblazer
    That port is a Thunderbolt 4 port, which supports HDMI 2.0. The 2.0 spec supports [email protected], so it should work. Have you tried to contact Caldigit yet? They may be doing something funky with the timing that the Mac supports but other machines don't...
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  • moolbkrammoolbkram Member Posts: 6

    Tinkerer

    Thanks.  If I remove the second monitor from the dock (Display port to HDMI), then the dock is able to use the USB-C connection to the 4K monitor.   Only when the dock is trying to drive 2 monitors does the 4K connection fail.   I do notice that my Macbook using the same dock drives the monitor at [email protected], apparently using the rest of the bandwidth for non-display data transfers.  Maybe it is something in my monitor configuration.
  • billseybillsey ACE Posts: 20,565 Trailblazer
    Can you test with the Windows laptop driving that screen at 30Hz instead of 60Hz?
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  • moolbkrammoolbkram Member Posts: 6

    Tinkerer

    I did try that last night, it didn't change.  I also changed the monitor settings (one allows high data streaming to make the USB ports on the monitor USB 3.0, or drops them to 2.0 to allow 60 Hz) -- again, no improvement.  When I use a separate HDMI cable to the 4K monitor (while keeping the connection to the Thunderbolt dock), the 4K is 60Hz and the USB ports on the monitor are active, as they are in all cases. 
  • billseybillsey ACE Posts: 20,565 Trailblazer
    With most monitors the USB ports are only a hub, not for video per se. What monitor is it?
    Click on "Like" if you find my answer useful or click on "Yes" if it answers your question.
  • moolbkrammoolbkram Member Posts: 6

    Tinkerer

    billsey said:
    With most monitors the USB ports are only a hub, not for video per se. What monitor is it?
    Not using the USB ports on the monitor for video, other than the input USB-C port.  The display is a Dell u2718q.   I chatted with Caldigit, who says this issue is common with Windows computers.
  • billseybillsey ACE Posts: 20,565 Trailblazer
    I wonder if the Caldigit is not passing USB-C Alternate mode through, that would block the video stream...
    Click on "Like" if you find my answer useful or click on "Yes" if it answers your question.
  • moolbkrammoolbkram Member Posts: 6

    Tinkerer

    billsey said:
    I wonder if the Caldigit is not passing USB-C Alternate mode through, that would block the video stream...
    It isn’t blocked if I disconnect the Display Port from the dock.  Caldigit is claiming the Acer isn’t properly sending two video signals through Thunderbolt 3 (the TB 4 from the Acer would be negotiated down to 3, which the dock supports).
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