I got my ys640 today, it turn on fine once. I paired it to the app, got it on wifi and walked away,
Since then I loaded it with pellets for it's initial burn in and now it won't turn back on.
Did you check the fuse? Do you have a competition cart? If so maybe the wires came off the back of the plug. Just a few things to check.
Bad board, the dealer was fantastic and came out and swapped a new board in, worked great after that.