Killed my uno after connecting 12v to DC connector?

Hi
Bought my first UNO R3 and it was connected via DC connector with 12v adapter (correct polarity). Board worked fine until I connected USB to computer at same time. Computer shut down and I disconnected everything. Now Arduino is no longer detected by computer but it seems to be working, at least script that was on it still does what it should. Did I killed USB chip? 16U2 gets hot ( thermal camera showed 80c and it's only component on board that is notably hot. 3.3 and 5v seems are ok when measured. Windows device manager does not show any activities when connecting Arduino.

Try unplugging the 12v power supply.
Wait for it to cool and attach USB again.
It should work with external power and USB…..…..

That's not supposed to happen...

I frequently have USB and (approx.) 12V at the same time on an Uno because I've got an op-amp circuit that runs from 12V and I normally power the whole thing from 12V. But when I'm programming or debugging, etc., I've also got USB plugged-in.

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Yes, I did that before to(not 12v I used 9v(I know the battery won’t last long)).
Photos of board?
Link?

Check for an open across the main fuse.

Fuse is ok.

Is anything else connected to the board?

No, nothing.

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You can check if the 16U2 is still good by doing a loopback test:

Disconnect the 12V for the test.

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Only connect ONE power supply at a time. To avoid this, i put a switch in the RED wire of the USB so I can program from the PC without backfeeding power.

3D printed box, but you can buy one if you wish.

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