My mower has started sparking at the brush heads and will not run at full power. I replaced the brushes but it appears the magnet ring is the problem. There appears to be some black soot on the ring itself. Is that an indication that this is the problem? It also gives that telltale, electric burning smell when it runs. I'm not sure I want to spend $70 on a new ring at this point. Time to throw the mower in the dumpster.