As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
90 DEGREE TACH ADAPTER PUT ON AIRCRAFT. WHEN ADAPTER FAILS, THERE IS NO RPM INDICATION TO TACH. PROBLEMS APPARENTLY VIBRATION INDUCED. SOME PROVISION SHOULD BE MADE TO REINFORCE UNIT, OR RELOCATE IT TO AN AREA NOT AS PRONE TO VIBRATION.