While trim mowing with my JD STX38, the blades all of a sudden stopped spinning. Everything seemed in order, so I figured it must be the PTO switch. I replaced the switch and still nothing. I realized that when I'm off the tractor while it's running (parking brake on) and I pull the PTO knob, the tractor shuts off, so the switch is probably not the problem. Does anyone know where to go from here?