As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FROM STOCK, INSTALLED IN AIRCRAFT DURING GROUND RUN, HAD NO NEEDLE INDICATION ON TRIPLE TACH INDICATOR. INSPECTED AND TESTED BY ACCESSORY OVERHAUL SHOP AND COULD NOT FIND ANY PROBLEM WITH TACH GENERATOR, IT TESTED OK AND WAS RETURNED TO SERVICE.