Monitor won't turn off anymore when computer is down

[Harm013]

Since a few days my monitor (S27B800TGU) won't turn off anymore when the computer is down.
I have this monitor now for about 2 months.

When I just had the monitor, and I turned down my computer, a window appeared that said that there was no HDMI signal anymore, and my monitor was going to turn off with a countdown of 3 seconds.

But since a few days it just goes into sleep without turning off (meaning you can see that the backlight is still active).

Can anyone please tell me why this is, or is it just a setting somewhere ?

[Harm013 · Accepted solution]

Received my monitor back from the store yesterday, and so far it seems to be working fine.
But it worked before for some time, so lets see if it still works correctly after a few months...

[Ajay-A]

Thank you for the update Harm013,

Please let us know when the issue returns. In the mean time I wish you much pleasure with your monitor.

With kind regards,

Ajay

[mm-jeff]

Just chiming in to let you know that we are experiencing a very similar issue on THREE Samsung S27B800TGU monitors at the same time.

All three monitors are connected to three Mac Mini M2 (2023) computers. We are noticing the following issues:

* After a longer session of work, users shutdown the Mac Mini, but the last image before the Mac shuts down seems to get 'stuck' on screen. In the case of MacOS this image is an empty desktop background. The screen does not seem to recognize that there is no HDMI signal anymore. Likely because of this, the screen does not go into standby mode, nor does it automatically switch off at any point. The brightness also never changes. Unplugging either the power cable or the HDMI cable 'solves' this issue, but I think you can agree that is not a solution.
It only seems to happen after a slightly longer session of using the screen. Our last testing sessions took between 15 and 60 minutes and that didn't seem to cause it, but now we're receiving customer complaints after 8-hour workdays using the screens and running into this issue.

We have also encountered an issue when running this screen with these Mac Mini's using a Thunderbolt cable. After a while, the screen's on-screen source menu (indicating you're connected via Thunderbolt) would not disappear anymore. We 'solved' this by hard-setting the screens to use the HDMI input instead, but we've kept the Thunderbolt cables connected to the Mac Mini's in order to use the Samsung screen's extra USB ports.

One of the screens has already been returned for repairs for another issue related to the LCD panel. The fact that ALL THREE of the screens show the exact same behaviour makes me believe this might be some sort of incompatibility between the Samsung screens and MacOS, or specifically Macs running on an M2 chip?

@Harm013 : If you don't mind, can you tell what kind of device you had connected to your screen when you ran into your issues?

[mm-jeff]

Quick update after I've had about an hour to tinker with the monitors.
Turns out this issue happens on 2 out of 3 of the Samsung monitors and it happens specifically if the Mac Mini tries to turn the display off due to inactivity. When that happens, the 'normal' monitor goes dark, shows a 'no signal' message and then goes into standby mode.
The 'faulty' two monitors flicker black for a fraction of a second, after which the image is frozen. For example if the screensaver was active, the last frame will the held indefinitely. If you then move the mouse, the Mac wakes up and you can continue working. However the monitor's buttons no longer work, the menu does not appear. If you shut down the Mac with the monitor in this state, the last frame will also be held until you plug the powercord to force a restart on the monitor. It does not seem to matter whether the monitor is connected via Thunderbolt cable or not. The only other USB attachments are Apple Mice & keyboards and Wacom tablets. The one monitor that doesn't have these issues does not differ from the faulty two monitors and all three Mac Mini systems run the same version of MacOS.

Curious to learn if anyone else has run into these issues. Seeing as this post is officially 'answered' I'm going to see if I can shoot a message to our supplier to maybe create a support ticket at Samsung for this.