Hey i think it might be difficult for you to repair it now. As same problem happened with me in past and they eventually leads me to buy a new one. If you are looking to bought the new one then you need to be extra attentive as knowing each ones pros and cons is necessary for a value for money purchase. You can read different articles related to it. I found one article which might help you:- https://theedgecutter.com/best-stepper-motors-for-cnc/ Read if you are thinking to bought a new one else you can search any one who can possible solve your prob.