Thunderbolt Display stopped working after Dell Update

I have a XPS 15 9570, and successfully used my Thunderbolt Display for more than 2 years. However, a couple days ago I ran Dell Update, which updated a few things, and now the XPS won't work with the Thunderbolt Display anymore

What happens is that it does recognize the new device, and I also get the "approve prompt screen" (see below for a screenshot), but whatever I select, it doesn't enable the screen, or the connected USB devices (like the keyboard and mouse). When I select "View Attached Devices" then the device is in the list, but the connection status indicates "Not connected" (again, see below for a screenshot).

I'm not sure which drivers it updated, but I'm sure one of the updates was a new version of the BIOS, as I saw the BIOS flash screen. I've tried a bunch of things to resolve this problem:

downgraded the BIOS (I'm now on 1.16.2, but I tried several, coming from latest 1.19)
went through all permutations of the "Thunderbolt Auto Switch" settings, inspired by this fix
tried to downgrade the Thunderbolt firmware, which didn't work, and is unsupported by Dell

Important to mention, connecting my MacBook to the Thunderbolt Display still works, so I'm also confident it's not the hardware that broke down.

Please, let me know if you need any additional information, or have ideas on how to fix this. Any help will be greatly appreciated!!!

Approve Prompt screen

Device recognized, but not "connected"

Responses(1)

C

cookbook

2 Posts

1

July 6th, 2021 10:00

I had the same problem after updating the bios to 1.19 a couple of days ago.

I had nothing on the USB C port for several days. No thunderbolt, no charging, no display port, dead.

I figured it's a controller firmware bug as it was fine the previous day.

I tried the following in this order:

- Shout at it (no fix)

- Flatten the battery and leave it overnight (no fix)

- Popped the cover off and disconnected the battery and left it over night (no fix)

- Downgraded to bios to last working version, 1.18.1 (worked)

During the flashing process you'll see it mention things like "flashing USB PD controller".

I did not try resetting the bios to default.

I now have a working thunderbolt port again. I hope that helps you

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