As others have already mentioned it is VERY UNLIKELY to be the coil or mechanism itself. The knocker not firing is the symptom and probably NOT the cause!
Get yourself familiar with the machine diagnostics (tests) as this will save you a LOT of grief in the future.
With these tests you can check lamps, switches, coils and many other things. You REALLY need to understand HOW to access this invaluable resource and probably before you even start hunting down this specific issue.