I'm having a bit of a problem with my Smoothieboard. While connected to Pronterface, Simplify3D, or Repetier Host if I warm the extruder and then click the off button the pin somehow gets written high and the temperature runs away. Same thing happens when I send m104 s0. I came in to a smoking hot end that had fried the thermistor as it passed through 600C. Any ideas on what would be causing the extruder heater output to go full power when S0 is written? I also have set the extruder max and min temps to 300 and 0 respectively. Thanks in advance.
That is very strange and very worrying.
First, please make sure you are using the latest edge version of the firmware.
Then, I would like to know the result of the M105 command when you boot up the board, and also right after you ask the board to heat, and also right after you ask it to stop heating.