I have an open ticket with Sovol already, they sent me new parts (nozzle adapter board and nozzle board communication cable) which I have replaced, but my issue persists.
Receiving the following error on the screen: !! mcu ‘extra_mcu’: Unable to connect
Within mainsail I get:
Klipper reports: ERROR
mcu ‘extra_mcu’: Unable to connect
Once the underlying issue is corrected, use the
“FIRMWARE_RESTART” command to reset the firmware, reload the
config, and restart the host software.
Error configuring printer
Has anyone else encountered this situation and replaced the parts recommended by sovol and then still had the persistent issue? Any tips or tricks to solve? Any experience I might be able to use to temper my expectations 
Thanks,
A couple updates to this in case anyone else is having the problem and this comes up in a search or something:
- My continuing ‘extra_mcu’ error (at the time of my original post) was user error. My replacement cable from Sovol did not have the same tolerance for the grommet for the screws as the original, so I didn’t notice any resistance as I tightened. I overtightened which pushed the screws heads through the holes and lifted the USB C connector, preventing the boards from talking to each other because, surprise, no longer actually connected. Attempting to troubleshoot and caught this during disassembly. Fixed it and the printer printed just fine for a couple weeks.
- I was getting ready to change nozzles so I wanted to raise the toolhead for better access. I hit the home button on the screen and the tool head dropped down to zero and the motors kept trying to descend. I powered off, restarted and the extra_mcu error returned. Troubleshooting here has led me to a bad umbilical cable (again?). Waiting for a reply from Sovol.