Mac laptop doesn't display on the screen/TV

Symptoms

When connecting a MacBook to the external HDMI cable on the screen, the screen flashes briefly and then goes blank. The display is detected under Screen Mirroring but neither the Extend nor Mirror options will display content to the remote screen. This seems to be an issue with the system in EXP-1686.

Possible Cause

This seems to be related to issues with updates contained with MacOS Tahoe and the video converter in EXP-1686.

Solution 1

Connect using an adapter with an HDMI port in the USB-C/Thunderbolt port of the laptop.

Solution 2

Log in to the podium (Windows) computer and start a Teams meeting (even if this is 100% in person). Join that Teams meeting from the Teams app on your Mac. Mute the mic and speakers and share the content from your Mac in the Teams meeting.

Symptoms

When connecting a MacBook to the external HDMI cable on the screen in a room with a TV screen, the screen flickers and displays a message about adjusting the resolution and then goes blank.

This seems to happen mainly on Macs when using an adapter to get the HDMI connection as opposed to Macs that have built-in full-sized HDMI ports.

Possible Cause

The TV is using the colour and resolution settings from the previously connected device that may be not be supported by the current HDMI connection. This is especially true when using an adapter to make the HDMI connection.

Solution

Use the Settings on the TV remote and go to the "External Device Manager" and select the "HDMI UHD Color" option

External Device Manager menu displayed when selecting the Settings option on the TV remote

Then, make sure the current connection (HDMI3 in most rooms) is not selected (not a green colour) - or to be safe just unselect them all (see below)

HDMI UHD Color options showing the feature disabled for all HDMI ports on the TV

From what we can tell, enabling of HDMI UHD Color option occurs automatically in the background when the connected device supports it. However, it doesn't seem to disable the option when the connected device/adapted doesn't support it. So, if the last device connected enabled the option and the next device/adapter doesn't support it, the only way to get it to work is to use the TV remote to disable it.