MacBook Pro running with external display in clamshell mode?

[PowerMacBook]

With my good old MacBook Pro mid-2012 I could run it with an external display/monitor in clamshell mode, as in closing the MacBook and use external keyboard, mouse and monitor.

When I try this with two monitors connected via HDMI, that doesn't seem to work.
Is this an HDMI issue, or is Apple Silicon simply not doing what we were used to?
Thanks!

 

[mattyboy7110]

I have mine working with two monitors but struggled to begin with until I realised the MacBook must also be plugged into the power before it will work.

 

[Christopher Kim]

What computer do you have now (noticed you mentioned Apple silicon), and how are you connecting the 2 monitors? (eg. are they both connected to laptop directly, and if so, through which ports / adapters? Through a hub?)

Except for the original M1 processors (2020 Macbook Air and 13" Macbook Pro) which only supported 1 external monitor, any of the new M1 Pro / Max laptops can support at least 2 external monitors (closed clamshell or with the laptop screen open) no problem.

 

[PowerMacBook]

MacBook Pro (16-inch, 2021)
Chip Apple M1 Pro
Memory 16 GB

Two monitors connected by HDMI
(one directly to the HDMI port, second through Belkin HDMI -> USB-C adapter)

I can have all three screens running, but prefer to have only the two externals on, and laptop closed.

 

[cyclingplatypus]

Wondering if you have it connected to a power source?

 

[LeeW]

Two things.

1. Is it connected to power?
2. You say the second is using an adapter, so not a straight USB-C to HDMI?

I suspect your issue is 2, they don't play well with adapters.

 

[mattyboy7110]

I have one on the HDMI port and one using the Apple USB-C to HDMI adapter (the one with a USB-C and USB-A port on it).

 

[Christopher Kim]

Assuming you do have the laptop plugged in (because if not, I assume the laptop is going to sleep when you close it), what exactly happens when it "doesn't work"?

You said it works with laptop screen open and both external monitors (so 3 total screens). But when you close the laptop lid, what happens? Do both screens shut off? Does only 1 screen shut off (and if so, which one, the one connected direct to HDMI port or the USB-C to HDMI one?)

 

[Riffbear]

Preferences - Battery - Power adaptor - Check Prevent Mac from Auto sleeping when the display is off.

 

[PowerMacBook]

Preferences - Battery - Power adaptor - Check Prevent Mac from Auto sleeping when the display is off.

will try that one, thanks!
(not near the monitors now)

 

[PowerMacBook]

Assuming you do have the laptop plugged in (because if not, I assume the laptop is going to sleep when you close it), what exactly happens when it "doesn't work"?

You said it works with laptop screen open and both external monitors (so 3 total screens). But when you close the laptop lid, what happens? Do both screens shut off? Does only 1 screen shut off (and if so, which one, the one connected direct to HDMI port or the USB-C to HDMI one?)

both external monitors go off

 

[PowerMacBook]

As I'm back at the monitors, I found out what is the issue.
Sorry for not having read properly what several posters already mentioned:

MacBook Pro must be on external power.

The battery of my old MacBook Pro was that bad, I always had it on the power outlet.
With the new one, I can easily live for a day without it, hence left the power adaptor at home.
Well, then it doesn't work.
Thanks.