Well, I have done some troubleshooting with it. The heating element is disconnected, but the problem persists. Since they are identical, I thought I would see if I could eliminate some possibilities. The motors of both work, and I swapped the switch PCB's with no change. The first unit still turns on for a while, the second doesn't come on at all. The main PCB has a part that touches the machine's frame with a thermal paste. If it is not in contact with the frame, then the motor only spins at it's fastest speed regardless of the speed setting. I replaced the thermal paste with fresh paste, but no change. I used an infrared laser thermometer to see if any part may be overheating. One small part circled here gets hot. The thing seems to turn off when this piece reaches 140 F, which only happens if I use a medium to slow speed on the motor. It gets hot at higher speed, but not hot enough that the motor shuts off.