MGL Avionics User Forum

Hi All!!
I have a problem with my IEFIS Challenger lite. I have an American champ with a C90 installed. I have connected the sensors to my RPM (one for each magnet) so it works perfectly up to a revolution of about 1300rpm. After that, the meter jumps up to 1800 for no reason. I have not touched the throttle. Then it can jump up and down until I pull the throttle back to below 1300rpm. Has anyone had a similar problem? What have I done wrong!!

Sounds like you have not installed a inline resistor and not selected the correct RPM sensitivity.

Typically you need a 10-40 kohm resistor inline from the magnetos. The exact value varies between magnetos and there does not seem to be an easy way to find out. Easiest is to just use a trimmer (say a 50K) and tweak it for best result.
The RDAC must have ballast OFF, filter ON, High gain OFF and adjust sensitivity with blue trimmer.

I am installing a IEFIS Challenger & RDAC with a Lycoming O-540. RPM indicates 10% of actual RPM (150 while at 1500RPM). I tried moving the Ballast jumper but then got no indication. Suggestions?

What are you using as pulses per RPM in your RPM setup and what type of pickup are you using ?

UMA T1A9-2 sender, 1.5 pulses per revolution.

Found it. details later.

Hello gentlemen,
I had the problem with Lycoming 540, Bendix mag
First - the window was wrong
Second - it was need to adjust sensitivity
hope it will be helpful to anyone in the future