I had a problem as well with my turbo lock ball, but it may be a different problem all together. Will share it just in case there is something useful to you or someone else in the future. Mine was intermittent and did register a switch error. In turbo test mode it would often clear. I, too, checked optos and the optoboard. What I ultimately found was that the nut that secures the turbo impeller in place was lacking an anti-slip washer. Once installed, I have never had a problem since.