My board shows up as a USB serial device in device manager. 3.3V an 5V LEDs are lit. status LED flashes at around 1Hz. USB light is solid. Ethernet light is solid yellow. This boar used to work through YAT and I had my whole printer set up working and then one day I powered this on and it no longer would connect to IP. I troubleshooted for hours before giving up and attempting to reflash the board. I followed all documentation and bossa appears to have successfully installed the firmware but I cannot even connect to the board with USB now. YAT will show connected but if I send a command that should illicit a response IE M552 there is no response. This continues for any command. Please help I have spent 8 hours (all work day) attempting to debug this thing so I can use my printer again and this is beyond frustrating.

@Phaedrux Thank you for your response!

The board does not show up when connected to a computer.

The CPU will continue warming up until uncomfortable to touch.

I don't have access to the board right now for pictures but I did a rather thorough lookover and didn't notice any shorts or damage.

Purchased from Duet around 9 months ago.

This is a new build I am coming back to however, the board seemed functional a few months ago and I was able to connect to it and run gcode commands then. I am not sure what would have changed between then and now

Yes, I have done the trouble shooting manual already.

Let me know if you have any ideas for other things I could try to get the board connecting to my computer again.

Thank you again!

Here is my troubleshooting summarized by Perplexity:
Duet 3 MB 6HC Troubleshooting Summary
Issue Description
My Duet 3 MB 6HC board is not functioning correctly. The symptoms include:
Only the USB and 5V LEDs are lit (solid red).
The 3.3V LED is off.
The status/DIAG LED is not flashing.
When connecting both USB and Ethernet, the USB and 5V LEDs flash rapidly.
When using only Ethernet, no LEDs light up.
When using only USB, the USB & 5V LED flashes.
Troubleshooting Steps Taken
Initial Observations:
Board powers on with solid red LEDs (USB and 5V).
The 3.3V pads measure 3.3V, indicating the regulator is functioning.
Power Supply Tests:
Tested with both USB and PSU connected; observed USB, 12V, 5V, and V_fused LEDs.
Tested with only PSU connected; saw the 12V, 5V, and V_fused LEDs lit but no other activity.
Tested with only Ethernet connected; no LEDs lit.
Tested with only USB connected; observed flashing LED.
Voltage Checks:
Measured voltages at various test points; confirmed 3.3V at the pads.
Erase Procedure:
Attempted to erase the board using numerous procedures but no board state change.
Visual Inspection:
Inspected the board for visible damage or shorts, particularly around power components, no damage observed.
Additional Tests:
Tried different USB cables and ports.
Current Status
The board does not initialize properly in any configuration.
The CPU gets hot when powered via USB alone, which raises concerns about a potential hardware issue.
Request for Assistance
I would appreciate any insights or further troubleshooting steps from the community or support team.