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My MGL Extreme tach is flaky as well. My builder used a tiny tach too. Tachs match most of the time.

Hi Mark
This may only relevant if you have the RDAC XF. With your pickup from the P lead definitely use the 10k ohm resistor. With the DIP switch positions try, Noise ON , Ballast OFF, Gain OFF. You should be able to fine tune to a steady reading from that using the sensitivity pot screw. The only settings in the display should be pulses per revolution, max/min RPM and alarms. The disadvantage of using the P lead is you either need 2 RPM displays or live with losing the tacho when the mag switch is turned off.
Steve
Sonex 892

Hello Everyone,

My apologies for digging up an old thread, but I continue to have issues getting a reliable tach reading from my Jabiru 3300 and MGL XF RDAC. I’ve talked to Michigan Avionics and Jabiru USA and get the same answer…good luck!

Ultimately it seems like there are 3 ways to get a tach reading: - a feed off an alternator output, a feed off a coil P-lead, or a Hall Effect Device. Everyone tends to agree the alternator output offers the highest chance of success but there has been no guarantee of anything working.

For me personally, it appears the alternator output feed has given me the best results but I still have an RPM range (1600-2300 rpm) where the system simply won’t read. For those with the same setup, I’m curious if anyone has done a resistor or diode of some type to make the signal more readable.

I’m not good at the electronics stuff but I’m more than willing to try and add or modify the sensor lead to get a more reliable signal. Has anyone found good luck with a resistor or something similar?

Thanks everyone!

My Grand Rapids Technology manual suggests another option to try. They show a method to use a pick off point off of the trigger side of an ignition coil. It's old school but might work. I currently am using the p-lead method on my Aerovee and have a stable reading using a 27K resistor. Down side is I lose the tack reading on mag check and have to compare RPM drop by ear. I probably at some point in the future will change to a hall effect solution if I can find a sensor that doesn't cost an arm and a leg.

Interesting. Okay thank you. I had a 10K resistor in there but that makes it seem like it’s still a dirty signal so maybe I’ll try that as well. Use a bigger resistor and see if that cleans up the signal a little.

Thanks for the thought!