I have a Samsung monitor, and my MacBook Pro is connected to it via USB-C,
both for power and for the video connection.

If the MacBook goes to sleep after some activity, the Samsung display notices
it, and shows a notice that it will also go into standby mode.

Fine.

But then, in a cycle that repeats every few minutes, the MacBook wakes up
because something has changed related to its power input (i.e. it behaves as
though the power has been plugged back in, flashes the battery symbol on the
screen for a moment) and then all goes dark again.

Meanwhile, the Samsung display says once again: going into standby mode.

It does this indefinitely, meaning that the screen is actually off only for a
few seconds each time.

I'd love a) to know what's actually happening, and b) for whole lot just to go
to sleep and stay asleep, while charging the MacBook. Which is what another
USB-C monitor I have (Lenovo) does without fuss.

Daniele

D.M. Procida <daniele-at-vurt-dot-org@invalid.com> wrote:
>
> But then, in a cycle that repeats every few minutes, the MacBook wakes up
> because something has changed related to its power input (i.e. it behaves as
> though the power has been plugged back in, flashes the battery symbol on the
> screen for a moment) and then all goes dark again.
>
> Meanwhile, the Samsung display says once again: going into standby mode.
>
> It does this indefinitely, meaning that the screen is actually off only for a
> few seconds each time.
>
> I'd love a) to know what's actually happening, and b) for whole lot just to go
> to sleep and stay asleep, while charging the MacBook. Which is what another
> USB-C monitor I have (Lenovo) does without fuss.

There is a setting called 'Wake on AC change' - I'd guess the monitor going
to sleep causes an 'AC change', which wakes up the monitor, now the laptop
is awake, then after a few minutes it goes to sleep, which causes an 'AC
change'... etc.

From what I read, it appears in System Information but I can't find where
it's changed. However there is 'clamshell mode' which may be related
- the idea being the laptop will turn on when power is applied, even when
the lid is closed. Maybe you have somehow enabled this mode?

https://www.alphr.com/how-to-close-macbook-and-use-monitor/

Theo

On 5 Oct 2023 at 17:31:16 BST, "Theo" <theom+news@chiark.greenend.org.uk>
wrote:

> D.M. Procida <daniele-at-vurt-dot-org@invalid.com> wrote:
>>
>> But then, in a cycle that repeats every few minutes, the MacBook wakes up
>> because something has changed related to its power input (i.e. it behaves as
>> though the power has been plugged back in, flashes the battery symbol on the
>> screen for a moment) and then all goes dark again.
>>
>> Meanwhile, the Samsung display says once again: going into standby mode.
>>
>> It does this indefinitely, meaning that the screen is actually off only for a
>> few seconds each time.
>>
>> I'd love a) to know what's actually happening, and b) for whole lot just to go
>> to sleep and stay asleep, while charging the MacBook. Which is what another
>> USB-C monitor I have (Lenovo) does without fuss.
>
> There is a setting called 'Wake on AC change' - I'd guess the monitor going
> to sleep causes an 'AC change', which wakes up the monitor, now the laptop
> is awake, then after a few minutes it goes to sleep, which causes an 'AC
> change'... etc.

That sounds pretty much like what I am experiencing - though as I noted, only
with this particular display.

> From what I read, it appears in System Information but I can't find where
> it's changed.

I found some references to it, but it seems to be a very old setting, from
2006 - https://www.macuser.de/threads/wake-on-ac-change.194967/.

I can't find it on my machine though.

Daniele