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I think my USB C output signal for an external monitor has died after upgrading to macOS Catalina. Tried all the advised workarounds without success.

I think my USB C output signal for an external monitor has died after upgrading to macOS Catalina. Tried all the advised workarounds without success. Is this a known bug? Is there a patch or upgrade for OS to sort this out?

MacBook Pro 15″, macOS 10.15

Posted on Mar 30, 2021 8:24 PM

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Posted on Mar 30, 2021 9:13 PM

Have you tried a different cable?


Have you used that same USB-C port for another device to check that it is working?


Have you looked in About This Mac => System Report => Graphics/Displays to see if your display shows up? Have you checked under Thunderbolt to see what is showing up as connected?


Have you looked for and used a reset button on the display?


Have you reset the SMC on your Mac?


Have you tried the display with a different computer?


I don't think the Catalina upgrade was the cause of the problem. Upgrading the MacOS is accomplished by writing files to the boot drive. Files are constantly being written and removed from your physical drives through normal operation.

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Question marked as Top-ranking reply

Mar 30, 2021 9:13 PM in response to alexinHongkong

Have you tried a different cable?


Have you used that same USB-C port for another device to check that it is working?


Have you looked in About This Mac => System Report => Graphics/Displays to see if your display shows up? Have you checked under Thunderbolt to see what is showing up as connected?


Have you looked for and used a reset button on the display?


Have you reset the SMC on your Mac?


Have you tried the display with a different computer?


I don't think the Catalina upgrade was the cause of the problem. Upgrading the MacOS is accomplished by writing files to the boot drive. Files are constantly being written and removed from your physical drives through normal operation.

Mar 30, 2021 10:06 PM in response to steve626

thanks but still not working. Checked all the points you suggested. I bought a DellP2719H monitor and thought it would connect without any problems (I have used a Dell P2720 with the same computer without problems), but no can do with HDMI connection to USBC via a multihub. HDMI port on Dell definitely works, and reset SMC does not change anything.

Mar 31, 2021 6:03 AM in response to alexinHongkong

Does the HDMI connection work with any monitor? Maybe the hub doesn't work in the OS.

What is the make and model of the Hub? Have you searched for any similar problems with that hub.


Have you tried a different adaptor? If you decide to look for one, you need a DisplayPort to HDMI or Thunderbolt to HDMI, not USB-C to HDMI. The plug has a USB-C form factor, but it is not converting USB to HDMI.



I think my USB C output signal for an external monitor has died after upgrading to macOS Catalina. Tried all the advised workarounds without success.

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