Erratic tach problem solved

[woodmanrog]

A while back I reported on how our AFS 2500 tach had taken on a mind of its own and was giving erratic readings. We suspected a loose connection but were unable to locate it. I checked all of the pin connections, sprayed for corrosion and still "no joy". Last week we had to replace the mags and checked the sending unit and all looked well. Still when all was re-assembled, we had erratic or no reading at all on the display. I ordered a new sensor ($50.00 fro Dynon/AFS) and we decided to replace it and work backwards to the display if necessary. Well, it turned out that the 3 wires connected to the sensor bolt had pulled slightly loose from the bolt. Upon inspection when we unscrewed the unit from the mag, I noticed that the epoxy at the bolt had backed out slightly. It turned out that this had pulled the wires far enough out of the bolt to cause the erratic functioning. I believe that there wasn't enough slack in the wires and vibration eventually pulled out the connection. We replaced the sensor and all is now working perfectly. This was one of those problems that will drive you crazy till you find it. I tossed the old sensor unit yesterday but I will retrieve it and post a photo. Fly safe and in our case, keep the rubber revolving.