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Catalina update not recognising monitor

I am using a USB-C to HDMI cable to connect Mac Pro to external monitor. Never had a problem connecting to external monitor before but now no signal is detected and not showing any external display in the display settings.

I have already reset NVRAM, checked cables, adjusted settings etc with no fix. It has come on a couple times after leaving the cable connected for 15-20 mins but not always guaranteed? Any solutions?

MacBook Pro 13", macOS 10.15

Posted on Nov 5, 2019 2:57 PM

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2 replies

Nov 10, 2019 7:16 AM in response to lmccall476

Hello lmccall476,


Thanks for posting in the Apple Support Communities. I understand that your Mac Pro isn’t detecting your external display, and resetting the NVRAM, checking the cables, and adjusting video settings hasn’t resolved the issue. I’d like to help. 


For this issue, I recommend taking each of these additional steps:


Get help with video issues on external displays connected to your Mac


If you’re still having trouble, contact Apple Support for further assistance: 


Get Support


I hope this information is useful. Kind regards. 

Nov 10, 2019 7:26 AM in response to lmccall476

to get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences


For a MacBook Pro that has a working built-in display, the obvious choice is the Last one -- to hold the Option key in Displays preferences and look for the appearance of the (Detect Displays) Button and click on it.


Catalina update not recognising monitor

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