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Old 15-11-2009, 15:15   #1
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Auto Pilot Failure

I have a Navman Linear drive auto pilot. On my recent trip from South Carolina to St Mary's Inlet the unit became inoperable. I am getting a "Drive Error" messsage. It comes on and works for a few seconds but as soon as it need to make a substantial rudder movement it trip with the error code.

I do not see anything obivous wrong, no loose wires or leaking fluid. Any thoughts on how to diagnose the problem.

Cam
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Old 15-11-2009, 16:54   #2
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Couldbe any number of things.

The rudder feedback could be dead yet the dirve unit could be fine. The course computer needs to get rubber feedback as well as compass feedback to determine how much rudder its required. A call to increase rudder without getting rudder feedback could be either end of the problem OR be the course computer telling you it's not getting anything. You need to validate the parts before you can rule out what it is and is not.

1. Can you do a dockside calibration.

2. Can you do a sea trial calibration.

Just because you did it a long time ago it can be a good apporach to finding the real problem before you start throwing money around. Validate what it is not and go from there. You can disconnect the fluxgate and rotate it through 90 degree arcs in the slip to validate the compass is working. These are easy things anyone could do and get more details.
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Old 16-11-2009, 08:05   #3
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Paul,

I am presently offshore on the N. FL coast, (hand steering). I checked the RDU and it is connected and seems OK. The pump does make a groaning noise just before the unit shuts down.

Cameron
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Old 16-11-2009, 08:40   #4
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Quote:
The pump does make a groaning noise just before the unit shuts down.
Soinds like some type of power or hydraulic overload forces it to shut down.
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Old 16-11-2009, 09:10   #5
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Another check for your rudder feedback functioning is to disconect it from the control box and check the risistance with an ohm meter. Swing the arm thru 180*.The reading from 0-90 should be 1/2 of 90-180*. With ComNav the figures are 300 to 600 to 900 ohms. Not sure what other makes are, and ComNav use the black and the green wire. Check with your service technician.
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Old 18-11-2009, 13:04   #6
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Thanks for the helpful suggestions everyone. I must report that I was offshore Monday & Tuesday and was desperate for the autopilot to work. I went to the RFU and jiggled the wires and tapped on the unit itself and like magic the autopilot came to life. It took me from St. Mary's GA to Cape Canerneral, FL without a glitch.

Probably not a permanent solution but I think it confirms that the problem is in the RFU. The wires I jiggled were connected inside the sealed unit so I am not sure if the was the problem or the tapping with a small hammer made something connect.

I am thinking about ordering a spare RFU.

Cam

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Old 18-11-2009, 14:01   #7
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Sometimes I think thing work after a tap with a small hammer, because some unknown sense tells it that the next tap is with the BIG hammer.
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