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I recently bought a used Elgato Thunderbolt 2 dock off ebay and everything seems to be working fine apart from this display issue.

Here are some details of the issue:

  • The monitor is connected to the dock through the HDMI port of the dock.
  • Upon waking from sleep, the display flashes (the flash that occurs when a display is connected or disconnected) and the monitor no longer works and displays a 'No Signal'.
  • To get the display to work again via the dock, the mac has to be restarted.
  • Ethernet, USB ports and headphone/microphone ports of the dock work when this issue occurs.

Some steps I've taken in an attempt to solve/isolate the issue:

  • Connecting a display directly from the mini display-port/thunderbolt port of the Macbook works.
  • Reconnecting the display and thunderbolt cable does not fix the issue.
  • Power cycling the dock (taking out the power adapter and putting it back in) does not work.
  • Using the second thunderbolt port on the Macbook does not work.
  • Disconnecting the HDMI cable from the dock and using the second thunderbolt port on the dock to connect a display via a mini-displayport adapter does not work.
  • Using another Macbook (a different model, more specifically a Macbook Air) works fine.
  • SMC and PRAM resets have been done already. Does not make a difference.
  • Looking at the console, multiple log entries appear which seem to suggest that the HDMI port is being reconnected multiple times:

Console log

My Macbook Details

  • MacBook Pro (Retina, 15-inch, Mid 2015)
  • List item
  • OSX Mojave 10.14.6
  • Intel Core i7 2.8 Ghz
  • 16 GB DDR3
  • 1TB SSD/Flash Storage
  • Intel Iris Pro/AMD Radeon R9 M370X

I've recently done a clean install, coming from the OSX catalina beta. So suggesting this again is out of the question.

Any help is appreciated.

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1

I had this same issue and Elgato was unable to solve it so I just began plugging my monitor directly into my Macbook's (Retina mid-2014) HDMI port.

After updating to Catalina I thought I'd try it again but now my monitor (Samsung 27" full HD) wouldn't sync to my Mac though the Elgato HDMI port, however it would sync through a displayport-to-HDMI adapter plugged into the Elgato Thunderbolt 2 port. The problem of losing video after waking persisted, however.

Finally I tried another monitor (LG 24"Full HD) which I had in the house. It worked perfectly and so far doesn't have the issue of losing video on wake. I'm reporting all of this to Elgato once again and will add additional information if they can provide a fix / explanation of why this works with LG monitro but not Samsung.

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  • I've actually solved this issue completely. My posted solution did not work however i've noticed that the thunderbolt cable was cracked on both ends which lead me to suggest that there was a bad connection between the dock and macbook. I've since then replaced the cable with a brand new one from apple and now has completely fixed the issue. – mclarence Jan 1 '20 at 12:33
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The actual problem was the thunderbolt cable itself. The cable was cracked on both ends, meaning that a good connection could not be established between the dock and macbook. Purchasing a brand new thunderbolt 2 cable from apple has solved this issue completely.

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