Dan's website says the motor is spec'd for 60Hz (what we use in the US) but I wonder if the control unit (or any of it's components) might be 50Hz,
as used in China?
I don't know squat about electronics, so take that with a pound of salt. I only raise it because a friend bought some fancy industrial sanders for his flooring business and had trouble with every one of them. The US distributor and the manufacturer (in Europe) finally figured out that our 60Hz power frequency wasn't playing nice with their electronic bits designed and tested for 50Hz...