@Phaedrux This was very helpful, thank you! I can connect to the board using USB again. I am having significant issues with getting connected to the web interface though as I can't get any signal through the ethernet port. Here is a summary of my troubleshooting:

The board is powered with 24V and responds to commands sent via USB using YAT. Despite configuring the network settings and connecting the board to both a router and directly to a PC, the Ethernet connection remains unresponsive. Notably, the Ethernet port's LED on the Duet board displays a solid yellow light.

Troubleshooting Steps Undertaken:

Checked Duet Network Configuration:

Executed the M552 command and confirmed that Ethernet is enabled with IP 192.168.2.1.
Set the PC’s IPv4 address to 192.168.2.10, ensuring both devices are on the same subnet.
Verified that the M553 command shows the netmask as 255.255.255.0.
Checked Ethernet Connection on PC:

Verified that the Ethernet port on the PC functions correctly by successfully connecting it to a router.
Attempted to detect the Duet board on another computer but observed no network activity.
Tested Direct and Router Connections:

Connected both the Duet and the PC directly via Ethernet—no connection detected.
Connected both the Duet and PC to a router—while the PC's Ethernet port LED lit up on the router, there was no LED activity corresponding to the Duet’s connection.

Verified Network Adapter on PC:

Checked the PC’s network adapter settings and confirmed that the Duet’s Ethernet connection does not appear as a connected device.
Ruled out potential software interferences such as firewalls or VPNs.

Any idea what I should do here? I have now spent many hours attempting to debug this ethernet connection bug.

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.