I tried to reply to this thread - MacBook Pro detects external monitor but shows black screen.

Unfortunately I don't have reputation to do so...

If you are having troubles with a black display it could be that your Mac has onboard graphics and a dedicated graphics card.

The full issue I had was a 2018 MacBook 15inch using two hdmi to usb-c connectors, only one display would ever have an image, the other was black.

As soon as I turned off Automatic Graphics switching (Apple Icon > System Preferences > Energy Saver > Tick Box for Automatic Graphics Switching) the problem immediately ceased.

Hope this may help some others with the same issue as me.

Edit: Ensure you do this for the relevant mode of use. You can change this setting for both using battery and being connected to power

  • Great start Michael. Be sure to add the answer to this problem in the answer section. We love it when people get the answers set - self answer is fine. – bmike Feb 3 '20 at 1:11

See my question as my answer. I wanted to post as answer in the linked thread but I was unable but I wanted to give back to a site that has helped me in the past

  • Thank you for posting. All we ask is the question be brief and the answer be put as an answer. – bmike Feb 4 '20 at 4:01

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