Duet damage after headbed exchange?

Regarding the burned heatbed issue , I was happy to get my replacement heatbed after having the original bed roasted. Now I think I may have killed the Duet board:

last actions:
I assembled the bed, but right after first start something smelled burned. Not sure what it was, I do not see anything. Shortcut or whatever happens seem to be gone.
But something is wrong now, Can't get proper connection. What a sad evening..

When powering on, I cannot get connection over LAN, but Duet USB is recognized. On Printrface I can connect, I just get the nozzle temperature in in second interval. When sending any command it says "printer not online". This messages arrives via serial USB from printer.
On Arduino Serial Monitor I can readout the firmware version, but not the MicroSD config script. After checking the MicroSD on PC it seems also to be dead. Tried another MicroSD with a backup, but nothing more is working anyway. Also tried reflashing the Firmware without success. I think, the SD Card line has been killed and maybe some more.

Voltage 5V and 12V are present. I checked the circuit diagram if there are any SMD fuses on the board, but could not find anything.

Is there anything more I can check?

thanks in advance

Take a look at component L7 which is by the corner of the chip nearest the SD card socket, and see if it appears to have overheated.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

L7 looks good. U1 not good. It's the Atmel. Surface isn't even on one position with a small bulb and temperature is high after powering on. 1 or 2 sec to burn finger.

I suppose a follow up damage due to a warranty exchanged part is not covered by warranty..?