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I have started experiencing a strange problem. I have a MacBook Pro 14" 2021, and an LG UltraFine monitor that's connected to it through a thunderbolt cable. The monitor charges the computer. It also has a speaker, mic, camera, and USB ports. One of the ports is used to connect to LAN.

Everything used to work fine, but recently something happened. Once in a while, all these devices (camera, mic, USB) suddenly disconnect. The monitor still works OK and still charges the computer.

I don't even know how to start searching for a solution to this problem

I saw this thread but the solution proposed there (connecting another USB cable between the computer and the monitor) didn't work.

EDIT I started noticing a subtle hiss from the thunderbolt cable connector every time an image on display changed. This gave me a hint that the cable might be damaged. I bought a new cable, and everything worked OK for one day, but the problem came back.

Ten days later I tried to connect the computer to the monitor using a TB cable, and connecting it to the power via the MagSafe cable. It didn't solve the problem.

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  • Have you tried another Thunderbolt cable? What is the exact monitor model?
    – jaume
    Oct 16, 2022 at 10:40
  • I thought it helped, but that was wrong. Oct 18, 2022 at 12:32
  • Too bad... What's the exact monitor model? Could it be that you are exceeding the monitor's power delivery?
    – jaume
    Oct 18, 2022 at 13:17
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    @jaume, the model is LG UltraFine 5K Display 27 inch. I only have two items connected to the monitor: the laptop and the network adapter. Also, I have had this monitor for several years now and had no problems until recently. I will try to connect the laptop to an external power source and see if that helps Oct 19, 2022 at 10:56

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How old is the Ultrafine? If it’s more than 2 years old, and you’ve been using the USB-PD feature, it’s probably about to die.

The Ultrafine is incredibly poorly designed. The entire unit hinges on the single TB connector on the back. When transferring power this connector gets very hot. Over time both thermal and mechanical wear cause stress on the connector causing pads and pins to separate. You get intermittent issues and eventually total failure. You can try to re-solder the connection, but it’s very difficult to do because of nearby components. It’s often impossible to repair. You can try getting a new logic board but they are very hard to source the correct model and about $700 for the board alone. Even as an authorized repair vendor, LG will repeatedly send you the wrong board because “it’s all they have”. Apparently they have a bunch of boards from the first generation of this display with all the RF interference issues and this is what they send out as replacements.

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  • I think you're right. The monitor is at least four years old. Oct 29, 2022 at 16:03

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