My Dell Precision 7740 won't charge from AC power anymore after experimenting with Thunderbolt dock.

GotNoRice

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EDIT: Mostly solved, see 2nd post.

I recently bought a Dell TB16 Thunderbolt Dock. My intention was to potentially use it with a new X870E motherboard via a USB4 port (since Thunderbolt is part of the USB4 spec).

But for now, I just wanted to test the Dock to see if it even worked at all, since it was a used purchase. I have a Dell Precision 7740, which has Thunderbolt ports and is actually one of the Laptops that is specifically listed as compatible with the TB16 dock, so everything should have been smooth sailing.

The laptop was already plugged in with it's own AC adapter. I plugged the 2nd AC adapter into the TB16 dock, at which point I heard a tiny fan briefly spin-up inside the dock. Then I tried plugging in the USB-C thunderbolt cable into one of the USB-C Thunderbolt ports on the Precision 7740. Nothing happened. The laptop didn't recognize that anything had been connected, it didn't detect any new devices, etc.

I was starting to wonder if the TB16 dock that I had bought was faulty. One simple troubleshooting step I tried was to simply swap the two AC adapters, since they are the same (both 240w) and the power port on the Precision 7740 and the TB16 dock are the same.

When I plugged the power adapter that had previously been plugged into the TB16 dock into the Laptop, the laptop would not recognize that an AC adapter is plugged in. I switched back to the first AC adapter that had been plugged into the laptop, and the laptop was now not recognizing that AC adapter either. I cannot get my Precision 7740 to charge using ANY Dell AC adapters at this point. I tried both 240w adapters, as well as a 130w and 180w adapter that I also have. In each case, the laptop continues to run on battery power only and indicates that no AC adapter is plugged in.

I also have an older Dell Precision M6800, which is also compatible with these same power supplies. I used it to confirm that ALL of the AC adapters are working fine. In each case, the M6800 immediately recognizes that an AC adapter has been plugged in. The Precision 7740 no longer works with any of them.

I don't really care about the TB16 dock. It was just a cheap experiment. I would have never even tried it if I thought that it was actually going to put my laptop at risk. I just really need to figure out how to get my laptop to run directly from AC power again. I assume that it must be related to the dock somehow, since that's when this all began, but I don't understand how. Either that or the power socket in the laptop just coincidentally died at that exact moment, but that would be quite the coincidence, and there is no visible damage to the power socket on the laptop.

Any input on where to go from here would be deeply appreciated. Thanks!
 
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Well, it seems like it was the Thunderbolt dock that caused the problem after at all. Trying to think of anything I could try, I dug up an older WD15 dock (non-thunderbolt Dell USB-C dock). When I plugged in the USB-C cable from the WD15 dock, the Laptop immediately began to start charging via the Dock (at only 130w). When I unplugged the USB-C cable, all of a sudden the laptop started recognizing AC power adapters again like normal.

Because I'm a glutton for punishment, I repeated the whole thing, trying the TB16 dock again, and sure enough once I plugged in the USB-C cable from the TB16 dock, the laptop stopped recognizing it's own AC adapter. Plugging in the USB-C cable from the WD15 dock once again fixed it. So this seems to be some setting that is being triggered/reset.

Anyway, leaving this here in case someone else has a similar issue in the future.
 
Updated TB drivers on the Dell site? New BIOS fix?

I'm pretty sure in this case that I was just sold a dead dock. The little light on the USB-C connector (common on most/all Dell USB-C docks) doesn't even light-up when you plug it in). I did try updating the thunderbolt drivers. The thunderbolt utility that is part of the driver package doesn't show that anything is plugged in.
 
Ah well it happens! At least it didnt end in total disaster.
 
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