My friends with the bobbin sensor issues in the Brother Dream machines all said the tech told them to use better quality thread.The new machines have such good technology in them that any slight imperfection triggers the sensors. He said sensors are all made by one manufacturer and sensor are made to sense any thing not up to specs. He can change out a bad sensor but if the imperfection is still detected it will cause the same problems. This is how they explained how the tech explained to them. So maybe not as detailed as he said it.