I received a repaired mainboard from Velleman and I installed it.
On the display is now :Err MINTEMP, and there is no reaction on commands like load filament or print from SD.
Min Temp means there is an open to the thermistor on the hotend or the bed.
You can identify which one in the software (under manual control) or on the LCD display.
the failing one should read 0C
for the hotend unplug Therm 1 on measure across the plug (not the board) you should see around 100K of resistance at room temp.
For the bed it’s the same thing except it’s Therm 2