@Phaedrux The replacement board has arrived and it immediately worked. We could install it in the printer an started configuring today. We have everything working, but one major issue:

Any motor connected to E0 only wiggles/vibrates but doesn't turn. There are no error messages in the console. We tested with several stepper motors. All motors work as expected on any port but E0.

As the built has independent dual z-motors, we can't just use E1 instead of E0.

How can we troubleshoot this?

This is the configuration for the drives:

; Drive Mappings (S0 = backwards, S1 = forwards)
M569 P0 S0                                                 ; Drive 0 goes forwards: X Axis
M569 P1 S1                                                 ; Drive 1 goes forwards: Y Axis
M569 P2 S0                                                 ; Drive 2 goes forwards: Z Axis Left
M569 P3 S0                                                 ; Drive 3 goes backward: E Axis
M569 P4 S0                                                 ; Drive 4 goes forwards: Z Axis Right (using E1)

; Motor Configuration
M350 X16 Y16 Z16 E16 I1                                    ; Set X, Y, and Z Microstepping with interpolation 
M92 X100.00 Y100.00 Z400.00 E397.00                        ; Steps per mm
M566 X840.00 Y840.00 Z48.00 E120.00 P1                     ; Set maximum instantaneous speed changes (mm/min)
M203 X15000.00 Y15000.00 Z900.00 E1200.00                  ; Set maximum speeds (mm/min)
M201 X4000.00 Y4000.00 Z1000.00 E600.00                    ; Set accelerations (mm/s^2)
M906 X620.00 Y620.00 Z560.00 E1000.00 I10.                 ; Set motor currents (mA) and motor idle factor in percent
M84 S30   

=== EDIT ===

This definitely comes from the config: When I boot a generic config, drive E0 works normal. Maybe you can see something in the config above, already? If not, I'll have a try again in a few days.

Thank you very much for your help @Phaedrux, I'll do that.

@droftarts my last reply was from memory, here's a screenshot of the port showing when the erase jumper was set:

Once flashed, no port is showing anymore.

Thank you, @Phaedrux

@Phaedrux got it directly from Duet, received it 2-3 weeks ago.

@droftarts Yes, I did. When flashed and rebooted there is no port at all. Neither on macOS nor Windows, with or without SD card. When I set the erase jumper I get a port. On macOS its tty.usbmodemXXXXX, on Windows its called bossaport(Com3). When I flash and reboot, there's again no port. The diag led has been always on so far.

Is there anything I can do right now, @Phaedrux ?

@Phaedrux thank you for talking to DC42 about this!

One more observation:
When flashed and power cycled, no serial port is shown.
When I short the erase jumper pins with the SD card in, no port is shown.
Only when I short the pins with the SD card OUT, the BOSSA port is connected.

For completeness: I verified the SD card once again, formatted FAT32 in Windows. All default config from the RepRap Configurator extracted to the card. Additional folders gcodes and macros.

Should the board respond in YAT even when no SD card is present? Or must the full system be loaded from SD?

@Phaedrux I just installed a VM with Windows 10.
Bossa can flash successfully.
YAT can connect but gets no answer after flashing but before power cycle.
After a power cycle, no port is shown.

Do I flash the correct binary?

@Phaedrux basically, yes. Just that the DIAG led is constantly on and that I only get the tty.usbmodem port on macOS after erasing the flash. Once flashed, I get no port shown.

The board is a refurbished unit that I got directly from Duet, INV-1594. It arrived about two weeks ago.