AHRS1 Hardware Fault (G3X)

[Flocker]

Has anyone received one of these messages?  I received one yesterday.  While flying, I had no Mode C, no TAS, and no OAT.  According to Garmin, I may have a faulty GSU25.  They are looking into it...

[Flocker]

Garmin confirmed it's a faulty GSU25. They will replace it at no cost. Once again, excellent customer service from Garmin!

[stroudj]

I am taking a G3X class with Pahan “the G3X expert”. I showed him your post, he agreed that the GU 25 is at fault.

Thanks,
Jim

[Tony]

Jim,
Would you mind telling us a little more about the class?  Sounds interesting.
Thanks,
Tony

[jetcat3]

Amen, sounds very interesting. More details please!

[Flocker]

Replaced the GSU25 today. Pretty simple task. The Pitot/Static/Magnetometer/Mode C calibrations/tests took longer than the installation. Problem solved.

[ronin5573]

Feb 2, 2018 0:06:01 GMT Flocker said:

Garmin confirmed it's a faulty GSU25. They will replace it at no cost. Once again, excellent customer service from Garmin!

I’m having the same issue.  Which one is one and which is 2 referring the the dual GSU25’s

Attachments:

[Flocker]

Got your PM. I honestly don't remember which one is which.

[Ed Midgley]

It’s the one with two sets of wires going into it. #2 should only have one set of wires going into it.
The picture isn’t Very clear but it appears to be in the foreground.
In the last five years I’ve had to replace three. Two had total failures and one was reading 7kts too fast.
Garmin has treated me very fairly. Two free and one half price.
Ed

[ronin5573]

Having just replaced my Garmin GSU I wanted to do a short write up for anyone going forward of what’s

Involved on the Tecnam 2008 with Garmin avionics. If you ever see a message on the G3X touch saying anything about reverting to ADC #2 or get RED X’S on your primary flight display such as airspeed, true airspeed, OAT and the wind vectors, then this might be your issue.


First go into the Configuration mode by holding down the menu button while starting up the screen. Go into the System information screen.
Go into AHRS 1 and if you see a RED X HARDWARE FAULT, then rest assured its time for a replacement GSU 25 or as they are called now GSU 25C which is the same part. Call Garmin Tech support and they where very helpful with a replacement unit [phone].


Here is how I replaced it. The dual ADAHRS units are located behind the rear bulkhead behind the seats. It’s a hard to reach place, so I removed Both seats to get back there and have better access. The seats come out with 1 screw and washer located on each inner seat rail and just push them forward holding the seat lock mechanism until they come all the way off the seat track tubes.


Then I removed the 10 screws to remove the back wall. The units are behind the wall. Mine were located on the far-right side looking backwards next to the remote transponder. On other planes they are in the middle. There are 2 of them and for me the #1 gsu25 was the one closest to the pilot seat. The other way to know is the #1 will have a much bigger wiring harness going to it. Still 2 wire connectors, just #1 has more wires. That’s the easiest way to identify because the serial numbers face the rear of the plane and there is no way to read the number until you actually remove it.


I removed the 4 screws located on each corner of the unit. This will free the unit from the bulkhead Then using a regular screwdriver loosen the 2 screws on each harness which will allow them to come off. Last is the 3 air lines that go to the GSU25. Pitot, static, and AOA. I tried for the life of me and couldn’t get the polyester lines to come off. Another forum member Ed Midgley suggested to use a heat gun. That works great. A little heat and they come off.

When the unit comes off just remove the 3 nipples which the lines attach to and install them into the new unit. Reassemble the new unit which is easiest to install the 2 wiring connectors, then reinstall it on to the bulkhead with the 4 screws and with a little bit of heat press on the new air lines.
Then reinstall your seats.


Sounds done but you’re not done yet. Turn on the G3X touch screen and you should get a air data computer not configured error pop up as a message which is great. Turn it all off and then move your airplane to a safe place with no metal structures within 20 feet and enough room to do a 360 at your airport.


Go into the g3# configuration screen by holding down the menu button on startup and then go to the ADAHRS button and then ADAHRS1. Go to UNIT ORIENTATION and select it to TUBES UP/ CONNECTORS FORWARD.


Next menu down is PITCH ROLL OFFSET and preform that test.


Next is to start the engine and preform the next menu item ENGINE RUN UP TEST.

Do that last test and then go back to the mail menu and hit magnetometer button and preform the interference test on the GMU11


Then the last step is turn your aircraft to the north. If your airport has a compass rose then use that. To be honest I used the compass app on my IPHONE and that worked fine. After your plane is facing north , make sure your front nose gear is turning right as you will have to turn the plane from the door opening on the pilot side so you can still see the screens. Preform the Magnetometer Calibration test AKA compass swing.  Just do what it tells you as you will turn the plane 30 ish degrees and then stop and then turn it until your back facing north.


Then save and exit the config screens and all should be back up and running.

I did a test flight right after to make sure and everything was working correctly using both ADAHRS units. Hit the HSI on the PFD and in that menu, you can manually select what AHRS the plane is using. They should both work.

I hope this helps someone in the future .

[ChiMike]

Thank you for the detail. Fingers crossed I don’t have to refer to it!