If its mechanically sound then you either have not enough power TO the coil or your ground is not clean which would not give you a 50V drop. Test power to the coil and also test that ground is actually ground and not floating... you need this to be 0V or very close so you get a 50V voltage difference across the coil.. if its above this then you wont have enough potential difference and will lose coil power. If the coil potential is sunk via a transistor.. then this should be your first place to look.. either the transistor itself, grounding from the Emitter or saturation at Base
