It seems the board has a lot of interference when using hardware PWM and it messes with the Bltouch servo signal.
The Hardware:From BigTreeTech an upgrade board for my Creality CR10 3D printer that I bought on Aliexpress for less than 25$.
Focus on getting the BLTouch 3.1 working...
Drivers BigTreeTech TMC2208 V3...
Visual inspection of the board and dodgy soldering of course! The Hotend connectors are not even connected properly... You can see the hole where the pin should have been...
The main reason I bought this board was to be able to print more silent.
TMC2208 V3 preconfigured for UART: check J2 where it has a 0-ohm resistor soldered.
Assembled it looks like this:
Vanilla Marlin 2.0.X not working with the TMC2208 at the moment. BUG in TMCSTEPPER.
Marlin compiled fine but the bltouch v3.1 does not work reliably, so it is pointless to invest any more time is this board for the moment.
Update from BigTreeTech: use software PWM for fans and heaters to make Bltouch more reliable. First tests seem to confirm this. More testing needed of course... It's a 25$ board after all...
26/6/2020: threw the board out as it is very unstable