If a user wants to replace their printrboard on an older dual-extruder machine they can indeed do so. Here are the requirements:
- Must use this or any older F4/5 compatible version. Dual extrusion is not compatible with current LED-capable firmware, which will not even read temperature of the 2nd or 3rd hot ends.
- Only channel "B" works. Channel "B" corresponds to hot end #3, so users should slice their models to use hot end #3 for their 2nd material.
- Both thermistor connections must have a thermistor connected.