Hello, i need some help trouble troubleshooting my treadmill. When trying to start the tread mill it runs for a few seconds and then trips the CB. After that every time I plug it in the GFCI. I have some experience with electronics troubleshooting but I am not an expert and some advice to get me started would be much appreciated.

 

Those boards are best removed and bench tested, the only thing is you require a 20hz PWM into HD2 to get it to run and test,
You could start by checking the SCR on the heat sink anyway.