Macbook with External Dock: Can't get external monitor working?

Hardware Hub
1

I just got the new MBP M4, and I have a Brydge Pro Dock. The dock requires that the laptop be closed to use it (it has a sleeve that the laptop slides into, so it’s impossible to open the laptop when it’s docked, by design).

I have the dock connected to its included 90W power brick (which powers the dock and charges the Macbook), and connected to a BenQ PD3420Q via USB-C cable (the PD3420Q supports video and USB over a single USB-C cable).

When I dock the laptop, the monitor doesn’t seem to receive signal (shows “No signal detected”). The dock does seem to be supplying power to the MBP.

When I connect the MBP to the monitor, directly, via the same USB-C cable, it works fine.

I removed the dock’s “sleeve” that keeps the Macbook closed, and connected the Macbook to the dock’s USB-C connector, and opened the lid, the monitor then started receiving video from the MBP.

So, the issue seems to be that the MBP /dock will work with the monitor , but only when the MBP is open, but of course, the problem is that this dock is designed to work only with the Macbook closed…

I haven’t used a Mac in a while (before the M-chip days), but my guess is that there’s a setting I need to set to get it to work. I set all of the “Turn display off” settings to “Never” and "Accept device “always.”

Other than that, I don’t know what I could set that would make this work…

2

That’s weird, to say the least. I don’t think you need to change any settings at all for it to work. The “Turn display off” AFAIK is about inactivity timeout after which the OS cuts off power to the displays (both internal or external). That shouldn’t affect the clamshell mode functionality.

The only time I remember to have issues with clamshell was few years ago, on an “old” M1 Macbook Pro - it was behaving like you’re describing, though the dock was different (and correspondingly old too), the TB3 SD5600T. Back then, it was an issue with my OS. Once I reimaged the laptop from scratch, everything ran smoothly.

I’ve glanced over your Brydge device, and the only thing that stood out to me was this FAQ (although I don’t really believe in this claim):

  1. The MacBook can’t output to an external display in clamshell mode (when the screen is closed) if no mouse and keyboard are connected. Pair them via BlueTooth or connect them to the ProDock before docking.