LG Ultrafine 5K Thunderbolt cable problem

[xecep]

I have an interesting problem with my LG Ultrafine 5K.

I'm using this monitor with my 16" M1 Pro

The monitor suddenly stopped working with the thunderbolt cable that came in the box. The cable charges the computer, but the monitor does not open. Also, nothing shows in the system report about the monitor.

When I try with the other usb-c cable that comes in the box, it works properly. But I'm not sure it's the right way to connect the display to my computer. Because this cable does not have a thunderbolt symbol

So I decided to buy a new thunderbolt cable and I bought belkin thunderbolt 4 cable.

Belkin cable worked for about 5 minutes, and it's dead. Also, my computer reset itself.

The interesting thing is these cables work in some other combinations.

I have an iPad, another 2k MSI monitor with usb-c input, and 16" m1 pro.

Belkin cable:
mac -> LG: charge but not work
iPad -> LG: works
mac -> MSI monitor: works

Original LG ultrafine 5k thunderbolt cable:
mac -> LG: charge but not work
iPad -> LG: not work
mac -> MSI monitor: not work

Another usb-c cable that comes in the box (without thunderbolt symbol)
mac -> LG: charges and works (I'm not sure it's the right way to use).
iPad -> LG: works
mac -> MSI monitor: works.

Does anyone have any idea about this?

Thanks 🙏

 

[klky]

I also have the LG UltraFine 5K and the sticker on the bag for the regular USB-C cable says "MacBook / iPad Pro" on it. I guess if it works with the MBP, you can continue to use it but presumably it won't be as powerful or fast. I believe it is otherwise safe. You can see if LG supplies the original thunderbolt cable as an accessory and/or test out other third party options in the meantime. Good luck!

 

[xraydoc]

I have an interesting problem with my LG Ultrafine 5K.

I'm using this monitor with my 16" M1 Pro

The monitor suddenly stopped working with the thunderbolt cable that came in the box. The cable charges the computer, but the monitor does not open. Also, nothing shows in the system report about the monitor.

When I try with the other usb-c cable that comes in the box, it works properly. But I'm not sure it's the right way to connect the display to my computer. Because this cable does not have a thunderbolt symbol

So I decided to buy a new thunderbolt cable and I bought belkin thunderbolt 4 cable.

Belkin cable worked for about 5 minutes, and it's dead. Also, my computer reset itself.

The interesting thing is these cables work in some other combinations.

I have an iPad, another 2k MSI monitor with usb-c input, and 16" m1 pro.

Belkin cable:
mac -> LG: charge but not work
iPad -> LG: works
mac -> MSI monitor: works

Original LG ultrafine 5k thunderbolt cable:
mac -> LG: charge but not work
iPad -> LG: not work
mac -> MSI monitor: not work

Another usb-c cable that comes in the box (without thunderbolt symbol)
mac -> LG: charges and works (I'm not sure it's the right way to use).
iPad -> LG: works
mac -> MSI monitor: works.

Does anyone have any idea about this?

Thanks 🙏

Sounds like something has a dead Thunderbolt controller (presumably the monitor) and is killing the chips inside the cable connector, and connecting just a USB-C cable bypasses the TB controller (or part of it) and isn't resulting in the same thing.

More than likely while the display will still function with the USB-C cable, the ports on the back of the display will either suffer speed loss or won't function at all. Does the camera in the display still work with the USB-C cable, I wonder?

Do you have other TB devices connected to your Mac that still work? Do be careful, because either your Mac or your Ultrafine is killing Thunderbolt connectors.

 

[joevt]

The USB-C cable will limit the display to 4K60 10bpc. If it connects as Thunderbolt 20 Gbps, then you can get USB 3.0 speed from the display's USB ports otherwise it would be limited to USB 2.0 speeds. You might be able to get 5K39 with a custom timing, but only on Intel Macs since M Series Macs don't support custom timings.

You need a Thunderbolt 40 Gbps connection for 5K60 10bpc.

 

[xecep]

Sounds like something has a dead Thunderbolt controller (presumably the monitor) and is killing the chips inside the cable connector, and connecting just a USB-C cable bypasses the TB controller (or part of it) and isn't resulting in the same thing.

More than likely while the display will still function with the USB-C cable, the ports on the back of the display will either suffer speed loss or won't function at all. Does the camera in the display still work with the USB-C cable, I wonder?

Do you have other TB devices connected to your Mac that still work? Do be careful, because either your Mac or your Ultrafine is killing Thunderbolt connectors.

Yes camera, hard drives, and ethernet adapter works with USB-C cable. (I have not test hard drive speed) Also I added system report screenshots with USB-C cable.

How can I test your theory? I'm trying to find cause of the problem. So I can go the apple store or lg support with the cause.

 

[xecep]

The USB-C cable will limit the display to 4K60 10bpc. If it connects as Thunderbolt 20 Gbps, then you can get USB 3.0 speed from the display's USB ports otherwise it would be limited to USB 2.0 speeds. You might be able to get 5K39 with a custom timing, but only on Intel Macs since M Series Macs don't support custom timings.

You need a Thunderbolt 40 Gbps connection for 5K60 10bpc.

Right now it's work with USB-C cable here is the results.

https://forums.macrumors.com/threads/lg-ultrafine-5k-thunderbolt-cable-problem.2353847/post-31316504

Actually I don't understand what is the custom timing is. I will learn another thing

 

[joevt]

Right now it's work with USB-C cable here is the results.

https://forums.macrumors.com/threads/lg-ultrafine-5k-thunderbolt-cable-problem.2353847/post-31316504

Your screenshot shows Thunderbolt connection at 20 Gbps. This means you cant't get 5K60. macOS only reports the frame buffer size (5120x2880). It's not showing you the output resolution (3840x2160).

But at least with Thunderbolt connection, you can get USB 3.0 speed. Look in the USB tab in System Information.app for a USB Bus and Hub belonging to the LG UltraFine 5K.
If you were connected without Thunderbolt, then there would be no new USB Bus and the USB Hub would be connected to the M1 Mac's USB Bus and the connection would only be USB 2.0.

Actually I don't understand what is the custom timing is. I will learn another thing

You don't need to worry about it because M1 Macs don't support custom timings. Basically, one would use the Custom Resolutions feature of SwitchResX to create custom timings and scaled modes. Maybe you can add custom scaled modes but that isn't enough to output 5K39.
https://www.madrau.com/srx_howtouseit/howtouseit.html

Anyway, you need to find a 40 Gbps cable that works properly to get 5K60.

You can get the current display mode by looking at one of the preference files (I'm not sure which one since I don't have an M1 Mac - I haven't seen the entire contents of a preference file so I don't know for sure if there's a distinction between frame buffer size and output size).
/Library/Preferences/com.apple.windowserver.displays.plist
/Users/yourname/Library/Preferences/ByHost/com.apple.windowserver.displays.[UDID].plist
https://gist.github.com/GetVladimir/c89a26df1806001543bef4c8d90cc2f8

If the preference file doesn't contain the info, or to verify the mode, try one of these:
https://github.com/joevt/AllRez
https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8
https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0

 

[xecep]

Your screenshot shows Thunderbolt connection at 20 Gbps. This means you cant't get 5K60. macOS only reports the frame buffer size (5120x2880). It's not showing you the output resolution (3840x2160).

But at least with Thunderbolt connection, you can get USB 3.0 speed. Look in the USB tab in System Information.app for a USB Bus and Hub belonging to the LG UltraFine 5K.
If you were connected without Thunderbolt, then there would be no new USB Bus and the USB Hub would be connected to the M1 Mac's USB Bus and the connection would only be USB 2.0.


You don't need to worry about it because M1 Macs don't support custom timings. Basically, one would use the Custom Resolutions feature of SwitchResX to create custom timings and scaled modes. Maybe you can add custom scaled modes but that isn't enough to output 5K39.
https://www.madrau.com/srx_howtouseit/howtouseit.html

Anyway, you need to find a 40 Gbps cable that works properly to get 5K60.

You can get the current display mode by looking at one of the preference files (I'm not sure which one since I don't have an M1 Mac - I haven't seen the entire contents of a preference file so I don't know for sure if there's a distinction between frame buffer size and output size).
/Library/Preferences/com.apple.windowserver.displays.plist
/Users/yourname/Library/Preferences/ByHost/com.apple.windowserver.displays.[UDID].plist
https://gist.github.com/GetVladimir/c89a26df1806001543bef4c8d90cc2f8

If the preference file doesn't contain the info, or to verify the mode, try one of these:
https://github.com/joevt/AllRez
https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8
https://gist.github.com/joevt/0c75b42171b3fb1a5248b4e2bee8e4d0

Thanks for the answer.

Here is the results.

I will buy another thunderbolt cable. Still I don't understand, why my new belkin thunderbolt 4 cable is dead in 5 minutes. It might die when I get a new one. Do you have any cable suggestion?

 

[mario24601]

Did you ever fix this issue?

 

[k2z]

Same issue here. Although I am not sure it's the cable. I wonder if the port on the back of the monitor is partially dead. My screen connects, but it no longer accepts Thunderbolt cables. Instead it takes a USB-C (usb 2.1) cable that I have from a projector. It passes power through, and has a connection of up to 480 Mb/s. Nothing else works, just this projector cable, and I've not being able to fix it, or diagnose it any further.