Product review (5 stars): super easy to install, very difficult to figure out that I needed this
Diagnosis was a bear, but I finally took the plunge and ordered this part based on my suspicion that the tachometer was the problem with my machine.  My 'guess' was right and installing this got my machine back up and running.  Installation is ridiculously easy, just remember to run the calibration routine from within the 'secret' service mode after changing this part.