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Old 14-06-2016, 05:26   #16
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

The esiest way to access it is via the back. The rudder reference unit is the one with it's own cable, basically you need to take it off and sit it on it's side with the motor cover downwards (the motor cover is the dome shaped round one) and then remove all the larger allen key bolts on the side now facing you, I think there is four long and one shorter,from memory. There are slots in the housing to help pop the cover off. You will then need to remove all the pins that the gears rest on so you can remove the arm. Note that 3 are steel but the fourth is plastic. once all that is out of the way you need to remove the next cover which holds the clutch and the reference unit is right there.

It is easier than it sounds and the thing is very cleverly designed and easy to work on.
Will take more photos if I ever have to strip it down again.
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Old 16-06-2016, 06:40   #17
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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Originally Posted by MondayNever View Post

The Class A drive unit has a built in rudder feedback sensor. It's not an external sensor system that I understand most autopilots have. My guess is that this sensor is going bad, though the unit is only a few years old.

Has anyone else encountered this?


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i've had three ruder sensors break in 3 months. Total crap product. Get and external sensor.
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Old 16-06-2016, 07:16   #18
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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i've had three ruder sensors break in 3 months. Total crap product. Get and external sensor.
Agility, did you have the Jefa drive (or the same version sold through Garmin)? If so, that's not great to hear! Was the drive getting wet?
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Old 06-07-2016, 17:45   #19
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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Originally Posted by Truxton View Post
The esiest way to access it is via the back. The rudder reference unit is the one with it's own cable, basically you need to take it off and sit it on it's side with the motor cover downwards (the motor cover is the dome shaped round one) and then remove all the larger allen key bolts on the side now facing you, I think there is four long and one shorter,from memory. There are slots in the housing to help pop the cover off. You will then need to remove all the pins that the gears rest on so you can remove the arm. Note that 3 are steel but the fourth is plastic. once all that is out of the way you need to remove the next cover which holds the clutch and the reference unit is right there.



It is easier than it sounds and the thing is very cleverly designed and easy to work on.

Will take more photos if I ever have to strip it down again.

This guy knows what he's talking about. I ordered the potentiometer he linked in his first post and installed it today. I unbolted the entire drive unit from under the deck so I could work on it comfortably, which turns out to be almost a necessity.

I took it apart based on the above instructions and it really was pretty self explanatory. Once I had access to the feedback sensor (potentiometer) I tapped it out of the housing then unsoldered the wires. Soldered the wires onto the new ones, which despite never having soldered before was totally painless. Reassembly was a little finicky but still easy. I'd suggest taking pictures to remind yourself of each step.

I did the dockside wizard and then went out for the sea trial wizard and everything performed flawlessly. We'll see if she holds up in the long run, but I'm hopeful.

Btw, Garmin wanted $800 to service it, not including wedging their bodies in my lazarette to remove the drive unit. The latter was the hardest part of the operation. Screw them. It cost $30 for the potentiometer and $10 for the soldering iron. 2 hours total time from when I first picked up a wrench to putting the the tool bag away.


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Old 08-07-2016, 07:23   #20
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

Congrats! That's a great savings!


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Old 09-06-2017, 04:14   #21
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

I have same problem on Bavaria 37c with 3 = trice replaced original JEFA unit.
no matter how many calibrations done, the rudder sensor is near limit or disengage.
the vessel is hardly 2 years old and neither Bavaria or Jefa want to take responsibility.

where can this potentiometer be bought ? I am docked this summer in the Dodekanes islands.

Thanks for any help an dsuggestion
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