thunderbolt 3 dock only pushing 30hz when connected via usb-c to macOS

[neal_o'shaquille]

i just recently bought a thunderbolt 3 dock (firecuda gaming dock to be precise), and am running into an issue with macOS limiting my refresh rates to 30hz when connected through it

the exact setup at the moment is:

my monitor (lg 38wk95c, 3840x1600 75hz) > the dock's thunderbolt-in port via a usb-c display cable > my MacBook pro 16" via thunderbolt 3 cable

as mentioned, this limits my refresh rates to 30hz when on my macOS side (running big sur). however, oddly enough if i switch to my windows partition via bootcamp, i'm able to select all the way up to the monitor's rated 75hz - without changing any of the hardware connections.

the issue seems to be the usb c connection on macOS, as when i connect the monitor to the dock via displayport i get the full list of refresh rates. the usb-c cable when directly plugged into the mac works perfectly fine as well. also if i use a displayport to usb-c cable from my monitor to the thunderbolt port on the dock, i get all of the refresh rates as well.

i want to avoid using the *only* displayport port on my monitor as i currently already use it for a different device and don't want to keep unplugging it out every time, which is why im trying so hard to get this to work. i've tried using switchresx and cscreen and neither have been able to fix the issue. also emailed seagate and am waiting for a response from them, although i really dont think this is a hardware issue.

if anyone smarter than i could assist that would be great!

 

[joevt]

Verify the dock is connected via Thunderbolt with Speed: 40 Gb/s x1, and Current Link Width: 2.

Use the AGDCDiagnose command to verify that the display is connecting with four lanes of HBR2. When using the USB-C cable, the manual says the USB ports of the display are supposed to be reduced to USB 2.0 so that four lanes of DisplayPort can be used. There's no onscreen menu option in the display to switch upstream between USB 2.0 and USB 3.0, correct?

I wonder if there could be a bug in the display where it selects USB 3.0 + two lanes of DisplayPort when connected to the Thunderbolt port of the dock? That doesn't make sense since you don't have that problem when connected to the Thunderbolt port of the MacBook Pro...

The FireCuda Gaming Dock has two Thunderbolt ports. The one with the laptop icon is supposed to be for the laptop (for charging). The normal Thunderbolt port is for downstream Thunderbolt devices or a USB device or a display. What if you switch the Thunderbolt ports?

In Display preferences, hold the Option key down and click "Scaled". Select "Show low resolution modes". Does 75Hz appear?

Maybe there's an issue with the USB-C cable.

Another option is - use a bidirectional DisplayPort to USB-C cable and connect it between the DisplayPort of the dock and the USB-C of the display. This will force 4 lanes of DisplayPort but it will disable USB ports of the display. In that case, a Belkin Charge and Sync cable or Wacom Link Plus can add USB 2.0.

 

[neal_o'shaquille]

Verify the dock is connected via Thunderbolt with Speed: 40 Gb/s x1, and Current Link Width: 2.

all verified to be true

Use the AGDCDiagnose command to verify that the display is connecting with four lanes of HBR2.

are you referring to when the display is directly connected to the laptop with the usb-c cable? or when it's connected to the dock?

When using the USB-C cable, the manual says the USB ports of the display are supposed to be reduced to USB 2.0 so that four lanes of DisplayPort can be used. There's no onscreen menu option in the display to switch upstream between USB 2.0 and USB 3.0, correct?

correct, no such option

The FireCuda Gaming Dock has two Thunderbolt ports. The one with the laptop icon is supposed to be for the laptop (for charging). The normal Thunderbolt port is for downstream Thunderbolt devices or a USB device or a display. What if you switch the Thunderbolt ports?

tried switching to no avail - both give the same result

In Display preferences, hold the Option key down and click "Scaled". Select "Show low resolution modes". Does 75Hz appear?

30hz, greyed out is the only option. even when i select super low resolutions i'm locked to 30hz

Maybe there's an issue with the USB-C cable.

maybe, but i've tried two and they both give the same result - also if the cable was faulty wouldn't it show issues when directly connected to the mac as well? for reference, here's the usb-c cable i'm using. the second cable is the one that came with the monitor.

Another option is - use a bidirectional DisplayPort to USB-C cable and connect it between the DisplayPort of the dock and the USB-C of the display. This will force 4 lanes of DisplayPort but it will disable USB ports of the display. In that case, a Belkin Charge and Sync cable or Wacom Link Plus can add USB 2.0.

also tried this using this cable - there's no output to the monitor when it is connected this way. ordered a bunch of cables with similar descriptions from different brands though to see if any of them work - will update if any of them the do. no output when using a displayport cable with a usb-c adapter either. using a thunderbolt 3 cable also doesn't work, even when directly connected to the MacBook. LG might be doing something funky behind the scenes with this usb-c port which is why these setups won't work. the only other option i'm considering is trying a usb-c female to displayport male adapter so i can use the current usb-c cable and plug in the displayport port on the back of the dock, but i an not sure if that would even work.

the biggest mystery to me is why the setup works perfectly fine under bootcamp and not under macOS... its hard to narrow down if it's strictly a macOS issue or a "peripherals-don't-speak-to-macOS-very-well" issue, which is why this is so frustrating

regardless, thank you for the thoughtful response!

 

[joevt]

are you referring to when the display is directly connected to the laptop with the usb-c cable? or when it's connected to the dock?

Both. For comparing.

also tried this using this cable - there's no output to the monitor when it is connected this way.

That cable doesn't say it's bidirectional so it probably only works with USB-C at the computer and DisplayPort at the monitor. You want to use USB-C at the monitor to save the DisplayPort input for something else.

ordered a bunch of cables with similar descriptions from different brands though to see if any of them work - will update if any of them the do. no output when using a displayport cable with a usb-c adapter either.

USB-C to DisplayPort adapters are usually one way - from USB-C computer to DisplayPort display.

using a thunderbolt 3 cable also doesn't work, even when directly connected to the MacBook. LG might be doing something funky behind the scenes with this usb-c port which is why these setups won't work.

Thunderbolt cables are usually just for Thunderbolt devices. The display does not support Thunderbolt. The new Apple Thunderbolt 3 Pro cable is supposed to work with everything. Also, Thunderbolt 4 cables are supposed to work with everything. No point getting expensive Thunderbolt cables if you have a USB-C cable available.

the only other option i'm considering is trying a usb-c female to displayport male adapter so i can use the current usb-c cable and plug in the displayport port on the back of the dock, but i an not sure if that would even work.

That looks like a USB-C to DisplayPort option. Again, you want USB-C at the display, so this adapter won't work.
Also, when posting an amazon link, you just need the /dp/B08F7KLQ48 part after the amazon.com.

the biggest mystery to me is why the setup works perfectly fine under bootcamp and not under macOS... its hard to narrow down if it's strictly a macOS issue or a "peripherals-don't-speak-to-macOS-very-well" issue, which is why this is so frustrating

The output from AGDCDiagnose command should tell us what macOS sees.

 

[neal_o'shaquille]

yeah i ordered a bidirectional cable as well as some others so lets see what works once they arrive - i'll post an update confirming which ones (don't) work for anyone else who happens to stumble upon this thread. now that i think about it, dp > usb-c is actually the ideal solution anyway as that will free up the extra thunderbolt port, so fingers crossed...

in the meantime, i ran AGDCDiagnose and your suspicions are correct - 4 lanes while connected directly to the laptop, and 2 when connected to the dock. any insights?

 

[joevt]

yeah i ordered a bidirectional cable as well as some others so lets see what works once they arrive - i'll post an update confirming which ones (don't) work for anyone else who happens to stumble upon this thread. now that i think about it, dp > usb-c is actually the ideal solution anyway as that will free up the extra thunderbolt port, so fingers crossed...

in the meantime, i ran AGDCDiagnose and your suspicions are correct - 4 lanes while connected directly to the laptop, and 2 when connected to the dock. any insights?

Are the USB ports of the display running at USB 3.x speed?

Sounds like a bug in the display. Talk to LG tech support and ask for a switch to four lanes DisplayPort + USB 2.0.

 

[ManuCH]

On my old 4K screen (I believe it was from Asus or Acer) I had a setting in the screen's hardware menu itself where I could force it to downgrade the USB ports to USB 2.0. Then I would always have 60 Hz. No idea if the LG screen has that.

 

[joevt]

On my old 4K screen (I believe it was from Asus or Acer) I had a setting in the screen's hardware menu itself where I could force it to downgrade the USB ports to USB 2.0. Then I would always have 60 Hz. No idea if the LG screen has that.

I couldn't find anything like that in the LG user manual that you can download. If that's the case, then the only way to force it is with the bidirectional USB-C to DisplayPort cable which doesn't have USB, or the Wacom Link Plus or Belkin Charge and Sync cable which have USB 2.0. Maybe the display needs a firmware update.

 

[neal_o'shaquille]

hey guys, I finally got all the cables in and have an update:

the only advertised bi-directional cable that worked for me was, ironically, the cheapest option - the Amazon Basics one for $16. using it, i'm finally getting the full 75hz while connected to the dock. again, i actually prefer this solution as i now have an extra thunderbolt port to utilize if need be.

regarding the LG display settings - joevt is correct, there is no option to downgrade the usb ports to force push the higher refresh rate in the monitor settings. so it seems like this is an issue with the display itself - and one that LG could possibly fix by adding such a setting. i might try emailing their support team to let them know of this issue, but i think it's such a niche use-case that i doubt it would cause them to add the setting in a future firmware update.

thanks all for your help!

 

[joevt]

hey guys, I finally got all the cables in and have an update:

the only advertised bi-directional cable that worked for me was, ironically, the cheapest option - the Amazon Basics one for $16. using it, i'm finally getting the full 75hz while connected to the dock. again, i actually prefer this solution as i now have an extra thunderbolt port to utilize if need be.

regarding the LG display settings - joevt is correct, there is no option to downgrade the usb ports to force push the higher refresh rate in the monitor settings. so it seems like this is an issue with the display itself - and one that LG could possibly fix by adding such a setting. i might try emailing their support team to let them know of this issue, but i think it's such a niche use-case that i doubt it would cause them to add the setting in a future firmware update.

thanks all for your help!

Their manual for the 38WK95C on page 24 says that USB-C is supposed to connect using USB 2.0 so something is wrong. You can ask them about fixing that at least.

 

[autotuner]

I have the firecuda gaming dock connected to my MacBook Pro 16" and my (2) 32UD99 monitors. All was working fine until the recent 11.1 Big Sur update. After the update I had the exact issue where the resolution rate was 30hz and was greyed out. There is another post about the 11.1 update causing issues with DP 1.4 and that DP 1.2 works. I did read that the firecuda uses DP 1.4 so I think that could be the issue here. For a temporary fix I purchased 2 x USB-C to HDMI cables. I have them taking 2 ports on my MacBook feeding my monitors. All is up and running now. It was well worth the $30 to get up and running again.

 

[vicfalc09]

I am having this same issue with the Belkin Thunderbolt 3 Pro dock. I can not get 60hz on my LG 27UK850 monitor. I want to be able to use the monitor USB ports (webcam,etc.) as the hub so I don’t have the option to use other connection on the monitor. Does anyone know of any docks that will keep me at 60hz?

 

[joevt]

I am having this same issue with the Belkin Thunderbolt 3 Pro dock. I can not get 60hz on my LG 27UK850 monitor. I want to be able to use the monitor USB ports (webcam,etc.) as the hub so I don’t have the option to use other connection on the monitor. Does anyone know of any docks that will keep me at 60hz?

Use the DisplayPort port for display signal, and USB-C port for USB signal.

Or use a Belkin Charge and Sync cable to get USB + DisplayPort from Belkin dock to the display's USB-C port. The cable will ensure you keep all four lanes of DisplayPort.

 

[vicfalc09]

Use the DisplayPort port for display signal, and USB-C port for USB signal.

Or use a Belkin Charge and Sync cable to get USB + DisplayPort from Belkin dock to the display's USB-C port. The cable will ensure you keep all four lanes of DisplayPort.

Can you send a link to the belkin cable your talking about? Want to make sure I’m looking at the right one.

 

[joevt]

Can you send a link to the belkin cable your talking about? Want to make sure I’m looking at the right one.

Belkin Charge and Sync Cable for Huawei VR Glass

Adapt HUAWEI VR Glass to connect with computer. Support DisplayPort high-speed transmission. Support HUAWEI VR Glass PC mode 3K 90Hz resolution. 4.5 meters in length, enjoy immersive VR games. 2 USB-A and 1 DisplayPort connet with PC, 1 USB-C port connects with Huawei VR Glass.

www.giztop.com

 

[vicfalc09]

That cable is 14 feet long. Trying to keep wire management down to a minimum. Is this going to happen with any thunderbolt 3 dock I try or is there potential to work (get 60hz) with a different dock?

 

[joevt]

That cable is 14 feet long. Trying to keep wire management down to a minimum. Is this going to happen with any thunderbolt 3 dock I try or is there potential to work (get 60hz) with a different dock?

You already tried a bi-directional USB-C to DisplayPort cable. They are shorter but don't include USB.

You can try different docks but it seems to me that it would be likely for them to have the same problem. You've only tried one dock so far.

 

[vicfalc09]

I need to use the hub (2 USB ports) on the lg monitor so I don’t think the usb c to display port cable would work as I would only be passing video to the monitor, right?

yes, this is the only dock I have tried so far.

 

[tommiy]

I have a 27uk850 running at 60Hz but I am using HDMI and a active display port to HDMI adapter with an elgato thunderbolt3 dock. Some words of caution even with my set up. MACOS upgrades are continually breaking the resolution and refresh rates. I can run 10.14.5 and everything is perfect with 60Hz when the MAC wakes up etc. 10.14.6 had issues with night shift and it trying to change resolution in the kernel every 10-100ms which resulted in high CPU. Catalina 10.15.1 on this exact same set up typically reverts to a much lower resolution when the Mac wakes from sleep. I have to disconnect the dock and reconnect. This is where the start of Catalina problems started for me. Later releases introduced many other strange related bugs. I can install 10.14.5 on a external SSD and it runs perfect so its only Catalina that had issues. This by the looks carried over into BS as well. All I can say is good luck because a working setup appears only valid for the single MACOS release.

 

[ManuCH]

Have you guys tried using SwitchResX to force 60 Hz?

 

[tommiy]

I have tried switchresx but as the problem is with Macos itself, switchresx does nothing for me. It reports the same responses. The issue is in the OS. 10.14.5 works perfectlyfor 60hz on my set up. in Catalina to get 60Hz I have to unplug the mac to reset the drivers etc and plug it back in. Once upon a time macs used to just work but thats been almost 18 months ago now where things have just been in a down hill slide. This issue is just one of those included in the ride unfortunately. My issues where worked through with Apple engineers with myself needing to devote alot of time to doing low level debug to prove issues with the kernel. After the promises of the next release will fix it, and indeed in some cases it dod, the release also created more issues than it started with. I've just rolled my mbp back to 10.14.5. However, the instability of macos with items just as the watchdog and windowserver problems (which is related to this as well) resulted in myself needing to move to a windows daily driver machine. Back on 10.14.5 I'm hoping to return to use my mac. In case your interested my windows machine has appoximtaely 1:3 crashes compared to the mac. So, reverting to Mojave I'm hoping to get back stability and reliability and never move post.....

 

[vicfalc09]

I went with the display port cable from the dock and I’m not using the hub on the monitor any more. Back to 60Hz thanks for the feedback.