I don't know ohms from alms so I'll need a simplified answer.

I have the Jabiru 3300 and Dynon 180 combo.  For 200 hours the tach has worked fine above 600 RPM; below that it flickered numbers between 250 and 500.  During flight, the RPM went to Zero and has stayed there since.  (Yes, I could still hear the engine running smoothly, smarty pants).

I have continuity between the alternator wire and the pin on the Dynon.  The alternator is producing voltage above 1500 RPM.  Disconnecting the regulator had no effect on the tach.

Red herrings?:  The ammeter has always been flaky; quickly changes positive readings from +1 to +8 and back but always in the proper direction.  When I turn off the alternator on my split switch, the Dynon reads overvoltage +50.

Thanks in advance to anyone who can figure this out.

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hi jerry,

     us in the sonex world using the jabiru 3300 , have had this happen. there are 2 leads off the alt. to get a pulse for the tach. 

a locking spade type terminal. check for broken wire, corrosion, poor connection of the joint, (pinch w pliers).

some have replaced this connector with something more robust. 

good luck, let us know what u find. 


Is there a resistor inline at the ignition switch on the P lead wire? If not, you might want to try placing a 30k resistor there.

Thanks for the inputs.  the problem was solved when I moved the RPM wire to the other alternator wire.  Bad connection or something wrong with the first alt lead?  Why does the alt have two leads anyway?


Alternators output alternating current. The leads switch rapidly from positive to negative, relative to one another. The voltage regulator is also a rectifier. The rectifier converts the A/C to D/C which is what the plane's electrical system needs. I am a bit surprised that what you changed fixed the problem. But if it works, it works.

The basic issue is that the A/C voltage coming from the alternator is not alternating relative to the aircraft's ground - which is as designed but not what the D180 needs. The D180 is looking for a voltage swing but wants to see it relative to ground. You my find that tack readings are erratic with changes in RPM and also in battery charge level and with what equipment is turned on. I explained this problem to Dynon years ago and they just did not understand the problem. I have fixed this problem on my airplane and 2 others, but that was years back. If you continue to have problems I might be able to help.


The spade terminals and/or their connections do go bad sometimes. That may have been the problem.

Hi Jerry et al,

Our 601XL with a Jabiru 3300 and a new Dynon Skyview Classic package had the tach reading fail and discussions with Dynon Tech service were helpful but unsuccessful. The final cure was to replace the voltage regulator and then everything worked again. This may be the quickest and most economical step in case of tach failure troubleshooting


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