Issue
I recently got a new Apple Studio Display to put my Dell U2717D monitor side-by-side to, you know, “be more productive.”
The M1 MacBook Pro had no issues driving both displays using a Satechi Thunderbolt 4 dock that I got earlier this year. Still, for some reason, my work computer (15-inch, 2019 Intel i9 and Radeon Pro 560X) couldn’t send the signal to both monitors simultaneously. For some reason, it always picked the Dell one. It did detect the speakers, camera, and mic on the Studio Display, but the screen wouldn’t turn on.
This was quite frustrating as there aren’t any buttons on the Studio Display after some trial and error and trying different cables (HDMI, DisplayPort, etc.) I finally made it work, but I couldn’t find a reason for this behavior, especially considering how new this 5K monitor is, unless I just search in Google for 5K monitors issues instead of Apple’s.
Solution
The issue is related to the Thunderbolt 3 (USB-C) controller that is in the laptop, and it’s been called out in this support article for the LG UltraFine 5K display:
The Intel-based 15-inch and 16-inch MacBook Pro models support two LG UltraFine 5K Displays. To use two LG UltraFine 5K Displays, you need to plug one display into a Thunderbolt 3 (USB-C) port on the left side of your MacBook Pro, and the other display into a Thunderbolt 3 (USB-C) port on the right side.
Note that only one of my monitors is 5K, the other is just a standard 1440p monitor, but I guess the limit is there, and the only solution is to plug the Thunderbolt 4 dock (with the Studio Display) on one side and the Dell U2717D on the other side. Long story short: It worked!
This setup is manageable, but I have lost the ability to swap between my personal and work computer with one cable with this limitation. Rick and I talked about the Studio Display and our impressions before getting mine. You can listen to it directly in Friction Log.
Side note, this monitor looks (and sounds) great! I am looking forward to the camera fix that Apple is working on.
Cheers!