My 150 started playing up this week, the stop switch was only working intermittently, thinking it was the wiring in the handle I took it apart to have a look, nothing wrong found inside, i ended up taking the clutch off to look under the plastics, it was then I noticed a screw under the plastic that was loose, I tightened it up put the saw back together and all was fine.
You can't see it but the earth must go to that screw, just a heads up incase anybody suffers the same type of problem.