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dual PG32UCDM on an MacBook Pro M4 with Pro chip

KHM
Level 7

I can't seem to be able to run dual PG32UCDM with an M4 MacBook Pro with the Pro chip.  Apple says it can run dual external monitors at 4k 144hz.  I am discussing with them currently how to get this working.  Wanted to check here if anyone has achieved this setup?

Also both monitors run fine on my M1 MBP with the Pro chip at 120hz.

I've tried TB5 direct to both monitors, TB4 direct, TB5 via TB5 OWC dock, TB4 via TB4 OCW dock, USB-C to DP cable rated correctly, USB-C HDMI adapter rated correctly (all of which work fine on the M1).

It all points for me at least to the M4, but hard to believe they've gone backwards since the M4 has native TB5 ports...checking to see if anyone else has this setup and experience.

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KHM
Level 7

had a few calls with apple support and they tell me this is a current known issue they are working on, my ticket was added to a larger ticket and said to expect an update to fix the problem. 

After reading a bit more now I’m doubting this as a solution.  Anyone with dual PG32UCDM experience on an M4 MBp?

justcallmecian
Level 7

I'm experiencing the exact same issue - with a 16" M4 Pro MacBook Pro and also a 14" M2 Pro MacBook Pro. 

I've tried:

  • Both monitors connected to a Thunderbolt 4 Dock (Corsair TBT200)  using USB-C to HDMI Cables. 
    • Only 1 monitor will display at a time. 
  • Direct to MBP - 1 Monitor connected with HDMI and the other connected with USB-C 
    • If both are plugged in, only 1 will display. If I plug out the one that is working, then the other display will start working
  • Direct to MBP - Both monitors connected with USB-C
    • If both are plugged in, only 1 will display. If I plug out the one that is working, then the other display will start working

What's strange is that when I initially set up the monitors yesterday they were working. Now I cannot get both to work at the same time no matter what I try. 

Did you make any progress here? I've been chatting with Apple Support today and they provided me different suggestions but none have worked. I'll be reaching out to them again soon.

KHM
Level 7

Well the chat with Apple was pretty useless, two people i spoke to in chat and on the phone did remote sessions on my MAC and observed the issue, saying that is not the way this should be behaving - swapping between monitors (I did like you get both working ‘once’).

I got them to book a Genius Bar appt and went in.  Person pulled out two monitors 60hz both and plugged them both into the TB ports - only one would work.  They went back for a discussion and came back and plugged one of the monitors into the HDMI and one into the TB and they both worked.  They said this was the only way it could work and only at 60hz (they could not confirm resolutions) but said it says so on the mac-tracker app (no idea what that is and didn’t look for it).  I just looked at the person and laughed and said wtf…the ports were TB5 ports etc..etc..etc.. but they just said sorry this is what it says in the specs..

I called BS, and said give me a replacement (I was 2 weeks outside my return window).  The person spoke to their manager and a bit of back and forth between them and me, i said f*ck it and said give me a MAX instead of PRO chip and I’ll pay the difference.  This was acceptable and i walked out with a MAX.

Went home - plugged it in and voila - drives the two monitors on my OWC TB5 dock 4k @ 120Hz.  (No HDR) I had to drop both monitors to 100Hz and i was able to turn on HDR.  So now i have two 100Hz 4k HDR via my OWC TB5 dock and one cable to the dock that i swap between the 16” M1 PRO and 14” M4 MAX.  I think the TB5 bus inside the PRO is f*cked on some but I’m just a fanboy.

 

I doubt it's an issue with the TB5 bus in the M4 Pro, as i'm also experiencing the issue on an M2 Pro which is TB4. With your M1 Pro, does it only work when using the TB5 dock? or were you also able to get it working using say HDMI and USB-C? 

I spent quite a bit of time on call with Apple today, and managed to get it escalated. They've sent all the details (they had me capture a sysdiagnose dump) over to the engineering team, so hopefully they can figure something out and get back to me. 

The 3 reps I spoke to today agreed that both of my machine should be able to drive the monitors. Even with my TB4 dock, that should be able to drive both monitors at 4K60. 

Really frustrating. 2 brand new (expensive!) monitors and I can only use 1 of them with my Personal and Work laptop.

Very frustrating for sure - you are in the same situation I was.  My M1 is work and M4 is personal.  

My M1 worked with any combination of cables or docks.  USB-c to HdMI, USB-c to DP, TB5 dock, TB4 dock two auSB-c cables direct to the M1. Always worked both 100hz.

now I have two external monitors with lid open or closed.

Interesting - I wonder why Hopefully Apple can figure it out on their side - because that's really my only option now.

Hi @KHM @justcallmecian ,

We sincerely apologize for the issue you are experiencing. According to your description, the MacBook Pro with the M1 chip can drive two monitors normally, indicating that the monitors are capable of receiving and outputting signals properly. Additionally, they work well with the MacBook Pro M4 Max. 

We understand that you have already contacted Apple Support. 

If you encounter any further issues with the monitors themselves, please feel free to reach out to us at any time.

We greatly appreciate your understanding and cooperation.

Thank you.

Please note that response times may be delayed due to upcoming regional holidays. For urgent inquiries, please contact your local service center. Thank you for your patience.

I've found a bit of a hack-y workaround in the meantime. 

I have an Elgato HD60X Capture Card. If I place this between my MBP and the 2nd Monitor, it gets detected and everything seems to work as expected.

It's quite a strange issue. I'm by no means a monitor expert, but I'm assuming that some sort of negotiation happens between the computer & monitor when plugged in to determine frame rates and resolutions. I suspect that when adding the 2nd monitor this negotiation is breaking down and ultimately failing due to the much higher frame rates with these monitors. This might explain why everything works fine when I add a capture card (which is capped at 4K60) in between. Again, I don't know much about monitors so this is just a very random theory. 

Whether this is an issue on the monitor side, or the Apple side, or a mixture of both is still to be determined.