Troubleshoot GI275/GMU11 calibration failure

[NicoN]

We have a Mooney M20K

today our shop tried to calibrate the GMU11

it works for the first steps, but finally it says "failed" and there was still 10 to 30° missing to complete the circle.

before that they did a firmware upgrade and now it wants 10 steps/36° instead of 12/30° before (they say)

What can we do? They tried 20 circles.
A more detailed instruction? Videos on that?

the GMU11 is installed in the right wing outside and aft of the panel with the OAT sensor. Seems to be a typical place for successful installation

 

[ArtVandelay]

Double check there’s no other wiring (servos, strobes, nav lights) near it.

Mine is in the tail on a shelf designed for this.

[Pinecone]

They should call Garmin.

[flyboy0681]

On 5/26/2023 at 2:15 PM, ArtVandelay said:

Double check there’s no other wiring (servos, strobes, nav lights) near it.

Mine is in the tail on a shelf designed for this.

Interesting you mentioned that. Mine was originally mounted in the tail, on a specially made shelf, and it just wouldn't calibrate properly. I finally threw in the towel and paid for it to be placed in the right wing, where the reading is now dead-on.

[65MooneyPilot]

I have some basic questions since I just installed one in my plane. What was the magnetometer interference test score? I am thinking it must have passed. Is the Gmu11 at or close to the wing sheet metal splice but not passed the aileron control tube and not close to the gear.  Is the ramp where they are trying to calibrate it is clean underneath, no rebar in concrete. Also no water or fuel lines either. We have had this discussion before on what is underneath the ramp. Thanks, let us know

[65MooneyPilot]

Here are a few pictures in the previous post, two of them I saved from the Mooney space pages and the other two are my plane during install. In my limited experience if it passes the interference test it should calibrate. 

[NicoN]

I can give some hints, finally it worked.

The shop tried  hard but was too fast turning.

We had the same problem: Our full circle ended  not with 360° but with 390° easily - so exceeding by far!

The solution: If you turn and stop, the indication on your GI275 seems to count down further.  If you stop whenever GI275 commands "HOLD POSITION", it s internal oistion might be finallay 2-3° more. Do this 10 times and you have a large error.

Solution:  stop the turn not when the GI275 says, but around 3-4° earlier. Then wait for the indication to settle. Conntinue turning really slow!!!!!! 0.1-0.2°/s maximum!

Stop, when the GI275 asks.

With this method, we ended dead at 360° and the GI275 simply said "complete"- No nice chime or something

 

The disappointing thing: the shop staff did not know this trick and also did not have a secret phone number of a Garmin evangelist!!!

Edited July 14, 2023 by NicoN