What should you do if a motor hums but turns freely by hand?

When a motor hums but turns freely by hand, it typically indicates that the motor is receiving electrical power but is unable to initiate its rotational function due to potential issues such as electrical overload, faulty starting components, or debris obstructing operation.

Blowing out the motor and trying to start again is a practical first step because it can help clear any debris or dirt that may have entered the motor and is preventing it from functioning normally. This action can potentially resolve issues related to dust buildup that can interfere with the motor’s operation. Additionally, it allows for the opportunity to check for any visible signs of damage or obstruction that could be influencing the motor's functionality.

Running the motor continuously when it exhibits a hum, without any further checks, could lead to overheating and damage, as it indicates an issue that needs attention. Checking the lubrication of the motor might be a valid consideration, but it’s less immediate than addressing the potential for debris affecting performance. Finally, replacing the circuit board is a more serious action that should come after troubleshooting simpler issues and understanding if there's indeed a significant electrical failure involved.