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RV-12iS Lane A indication, not quite right

M

Mike Buettgenbach

Active Member
New airplane, finished initial phase of flight test, no issues to speak of.

Now the background:
First attempt to do an engine run (few months back). Lane A and B indicate RED for 3-4 seconds, then go out . . . except for lane A; it goes to about half brilliance. No faults logged. After various conversations with the Vans guys, they said "no worries, go ahead and run the engine". Worked great.
After a couple of ground runs, I notice that it (Lane A annunciation) no longer has the half brilliance situation. All is normal.
Flew Phase 1 - all is good

Now the problem:
Flew today (about 6-7 hours total on the aircraft at this point), the Lane A light is doing it again. No faults logged, and all else looks/acts normal.
All interconnect has been inspected and metered to print.

After a fairly long conversation with the Van's guy (sorry, forgot his name but he was really good at electrical things), his conclusion was an internal fault of some sort on the ECU. . . But not a "log-able" fault.

Any ideas?
Thanks guys
MikeB
 
I can’t diagnose your issue, but I’d highly recommend joining the Rotax Owners Forum and post this question there. There are several highly knowledgeable guys on the iS portion that will likely have some suggestions. You can read posts without joining, but to post questions or respond to issues you need to join. It’s $25 or $30/year and in my opinion, we’ll worth the investment. Here’s the link to the 912iS portion of the forum. Good luck.

https://www.rotax-owner.com/en/912is-technical-questions
 
Mike Buettgenbach said:
New airplane, finished initial phase of flight test, no issues to speak of.

Now the background:
First attempt to do an engine run (few months back). Lane A and B indicate RED for 3-4 seconds, then go out . . . except for lane A; it goes to about half brilliance. No faults logged. After various conversations with the Vans guys, they said "no worries, go ahead and run the engine". Worked great.
After a couple of ground runs, I notice that it (Lane A annunciation) no longer has the half brilliance situation. All is normal.
Flew Phase 1 - all is good

Now the problem:
Flew today (about 6-7 hours total on the aircraft at this point), the Lane A light is doing it again. No faults logged, and all else looks/acts normal.
All interconnect has been inspected and metered to print.

After a fairly long conversation with the Van's guy (sorry, forgot his name but he was really good at electrical things), his conclusion was an internal fault of some sort on the ECU. . . But not a "log-able" fault.

Any ideas?
Thanks guys
MikeB
Click to expand...

I responded to you on Rotax Owners. Feel free to PM me as well. My best guess is to get in behind the avionics cover and start really looking with a magnifying glass. Other than that you may be able to pull the ECU and ship it to someone for analysis? Note sure what to do if the Hardware is actually faulty.
 
Not saying that this is your problem, but it is worth checking the LED resistors.
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The Rotax 912iS lane LED lights did not work in my friend's Kitfox. There was a faint flicker when the lane switches were first turned on. The lights worked fine when a 9 volt battery was connected to the pins in the HIC connector for the lights. So the problem must be in the Rotax harness or CPU or fuse box, right?
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NO
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After days of troubleshooting, we decided to remove the LED parallel resistor to see if that made a difference. Wow, that did it. The LED lane lights now worked. It turns out that the Kitfox supplied resistors were 1R5 (1.5 ohms), not the recommended 1K5 (1500 ohms). The purpose of those parallel resistors is to prevent the LEDs from glowing dimly when the Rotax solid state switch is off. A 9 volt battery has enough current capacity to power both a low value resistor and a LED. But the Rotax CPU must have internal resistance that limits the current.

Lesson learned: Check load resistance.
 
If I remember correctly, the LED light is pretty much directly connected to the ECU.. obviously the wiring takes it through the ignition module (pins 6,19) to the HIC module (pin 8, 20) , out the smaller HIC connector (pin 2, 8), then to the ECU.

It sounds like, assuming the problem isn't inside the ECU itself.. the problem is an intermittent ground along that path.. which could show up as a dim LED..depending on the resistors used, voltage, etc. I would not be surprised if one of those pins has backed out of its connector.. its happened a few times before in this forum.
 
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More info

Hi Rob - Just as you had noted, I looked last night and it is just "hard wired" to the ECU. Slim chance, but I metered the wires looking for any part of open or ground fault -- nothing out of the ordinary.
Guess I'll start the process of investigating ECU test/repair/replacement.

Thanks for the input
MikeB
 
The problem sounds like an intermittent connection of the LED parallel resistor.
Assuming that your LED has an INTERNAL parallel resistor,
try replacing the LED before replacing more expensive parts.
 
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If you can swap the Lane A and B LED circuits and B goes dim it will tell you it’s the LED.
 
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