Finally managed to update the firmware after trying most of the suggested solutions. However, it seems very random and inconsistent when the upgrade works. My findings are that it works fine with a USB 2.0 stick, but after tons of attempts (always with the same firmware file as I was sure that it was the correct one - just to rule that one out), I finally managed to perfrom the update. My problem was that I never received the "Update via USB" prompt, but immediately always got the error "No valid update files found. Please check your USB device and try again." I also tried recycling the power, tried both USB ports and USB2 and USB3 sticks. Even tried with the .zip, .Bin and renaming the file to exclude the checksum - all in vain. What finally made it work for me, was to disconnect all input cables (in my case the Displayport), then recycle the power and THEN I finally got the "Update via USB" prompt. The working setup for my LC34J791 which was running firmware v1002 was a USB2 4GB stick (FAT32), using the lower of the two USB ports on the back of the monitor and having a single file on the stick. The file name was "m-J7934CGAB-1009.0[C73C].Bin" (extracted from the zipped 1009.0 download).
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Hope this helps, but in my lenovo t590, it has 2 usb-c conecctions, a normal usb c, and a thunderbolt one. In the USB-C, everything works fine, but if i switch to the thunderbolt, the hub was gone. My fix was going to the Thunderbolt Control Center (hope your pc have one, or look after it in the driver/software of your machine). and then jus Enable it, seems like for security it wasnt fully activated.
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