There are multiple reasons for “locking up.”
First of all, you should be aware of how a motor works. If you give it power, the energy from the electricity turns into mechanical energy. But if you spin the motor with your hand, it will convert mechanical energy back into electricity (Which is how hand cranks work). That being said, if you spin the motor on a faulty circuit, the motor may be almost impossible to spin with your hand if there’s nowhere for the electricity to go. I would suggest trying to change the port for the motor first before changing the motor entirely.
If changing the port did not work, the next option is to check the cartridges. If you change the cartridges and the problem persists then the problem is the motor itself. Then I would suggest replacing the motor.