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Author Topic:   Simrad AP11 Autopilot Failure
6992WHALER posted 08-08-2011 09:19 PM ET (US)   Profile for 6992WHALER   Send Email to 6992WHALER  
I have a Simrad AP11 Autopilot.
J3000X Junction Unit
LF3000 linear feedback
LFI3000 Linear Feedback Interface.

The unit is giving a Rudd.Ang Failure message.
Under trouble shooting the probable fault is "Rudder feedback failure"
Recommended action: check cable, connections and installation of Ruder Feedback Unit.

I checked all the cables and connections and they look OK

I have not called Simrad yet, has anyone had this happen to them?
Is there a way to test the linear feedback or the feedback interface?

jimh posted 08-08-2011 10:23 PM ET (US)     Profile for jimh  Send Email to jimh     
John--Without having any knowledge of how this actually is designed, I would guess that the rudder angle feedback sensor is likely arranged as a potentiometer. I would begin diagnosis by

--disconnecting the cable from the rudder angle sensor to the main unit;

--using an ohmmeter, check for continuity and resistance on tbe cable going to the sensor;

--I would expect to see that there were three leads involved with the potentiometer; the resistance among and between these leads should vary as the outboard engines are turned to port or starboard;

--using a voltmeter, check to see if there is any voltage supplied from the main unit to the pins on the connector to which the rudder angle sensor connects.

It would be much easier to diagnose the problem if you could get a schematic diagram from the manufacturer.

jimh posted 08-12-2011 10:25 PM ET (US)     Profile for jimh  Send Email to jimh     
John--I found some SIMRAD literature on-line about the AP11 system. The rudder position sensor looks more sophisticated than just a potentiometer. You are going to need some more technical literature to delve deeper into this repair.
6992WHALER posted 08-15-2011 10:56 AM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     

I talked to Simrad.
They said to open up the LFI3000 Linear Feedback Interface and clean the connections inside the box.

If that does not work then I need to replace the LF3000 Linear Feedback or the LFI3000 Linear Feedback Interface.
There is no way according to the Simrad tech to test which unit is bad.
Usually it is the Feedback unit that fails but it might be the Interface. Of course the feedback unit cost $350 and the interface cost $160.
I hope to get a chance this week to clean up the connections. If that does not work then I will have to roll the dice and order one of the units and see if I guess correctly.

6992WHALER posted 11-23-2011 05:35 PM ET (US)     Profile for 6992WHALER  Send Email to 6992WHALER     


I cleaned all the connections and still received the "Rudder feedback failure" message.

I found a used LF3000 linear feedback on eBay.
It came today, I plugged it in and the system is working again.

So I will have to mount it but it looks like my autopilot is back in business.

jimh posted 11-23-2011 10:27 PM ET (US)     Profile for jimh  Send Email to jimh     
John--That is good news. It is always satisfying to make a repair yourself, and in the process save some money. And bydiagnosing and repairing the problem, you have become more familiar with the system and better able to maintain it in the future. Good work.

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