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

 

[AVDB]

Please attach photo of physical GMU 11 installation

Make sure that GMU location meet all installation requirements.
if it is required - replace metal fasteners into stainless steel
perform Magnetic Interference Test

my advice:
During calibration, taxi the aircraft in a good BIG nice circle - you will get smooth and precise taxiing

Magnetometer Calibration.pdf GMU location requirement, magnetic interference.pdf

[PT20J]

The GMU 11 is susceptible to electrical interference --  especially strobes. Might check that.

[Utah20Gflyer]

I had this issue recently, in the end we towed the plane by hand and got it the first time we used that method,  I think we tried 4 or 5 times taxiing the plane and it failed every time.  

[NicoN]

Success!

Using all your experiences and more we finally managed.

Our shop iniatially tried 20 circles burning 15! gallons and finally gave up. They wanted to move the GMU.

We tried and again and also did not succed for the first 2 attempts.

We always ended up not north, but overturning by at least 30-40° !!

It finally worked doing the first 30° of the 36° turn, then stopping to turn and waiting the still counting down degrees to settle

Then continue dead slow with only fractions of a degree until the "HOLD POSITION" command comes. Repeat.

It was obvious that something was different after a few steps: we always ended up dead on the targeted heading (compared with the whiskey compass) and the last step now ended exactly on magnetic north.

The GI275 gave only a simple "SUCCESS"

Please GARMIN: let the GI275 talk a bit more in detail about what was wrong, like "Your full circle ended with over-turning by x degrees. Take your time and turn slower"

 

Next issues will follow