Thank you Imran - I did email Felder a few weeks ago and they provided this same system diagram. Unfortunately the schematic is similar but not identical to how my machine is built (the wire numbers are not all the same and my machine has no fuses on the low-voltage system, for example).

These older machines with the Siemens main board are a challenge - if only a detailed board schematic were available it would be way faster to troubleshoot. I asked Felder about it and they said they don’t have one - they treat the board as a black box.?

At this stage I’m seriously considering either (a) ripping out the guts and building my own motor control circuit w/o brake, using an arduino to handle the switch logic, and reusing the selector switch, or (b) buying three-phase motors and using VFDs, again plus the microcontroller for logic.

i’d really prefer not to burn the 100 hours or so I know it would take me to do this though!