@micle546 remind me on Monday when I am back from formnext and I will look up L4. It's probably the same component as one of the inductors on the Ethernet module for Duet 2.
The W5500 chip is typically the first to fail when there is over voltage on the 3.3V rail. I suggest you remove the two failed ICs and then power up and check the voltage on the 5V rail. If that measures OK you could either replace the removed 3.3V regulator, or apply 3.3V externally, then see if the USB port appears. If so then run M122 to see if the stepper driver status is OK.