Hi Guys, I checked the wiring on the machine and it was correct so i removed the arduino and shield and replaced them with a new setup and i have set the 24volt motor to run direct from the power supply, and now everything works as it should. Possibly the problem was a faulty motherboard or shield or both, i don't know which. On the original setup the 24volt power supply was wired direct to the motor with a rocker switch to control the power so i don't see how 24volts could get to the USB cable. I guess that is not important now. Cheers Ron. (Thanks for your input to my problem).