NAVpilot 500 failed rudder test

[Brad Allan]

I recently bought a 2004 boat with dual helm stations and a NAVpilot 500. The previous owner said the autopilot worked until he replaced the head unit at the upper helm due to illegible LED readout. Now both head units look and read normally. Both heading readouts show proper heading, both units show proper rudder position. When put into auto mode from either station the unit doesn't show anything abnormal, it indicates auto mode, but the autopilot is not controlling the rudder at all. When in standby mode, if I read the manual correctly, I should be able to control the rudder with the left & right arrows, but nothing happens. Going into system setup, everything seems to progress properly until the "rudder test". When activating that it will turn the rudder all the way starboard, then only about 10 degrees back to the port, then display "rudder test failed". If I do a google search on this condition, it says most likely is air in the system. The boat turns fine in both directions from both helm stations. Can I bleed the autopilot pump separately from the helm stations? There is a junction block in the system after the point where the helm stations and the pump are plumbed together, and just before the rudder actuating cylinder. Do I bleed the pump there? See picture of the junction block.

 

[Johnny Electron]

The second station is connected in parallel so the entire system is bled as a system. Normally the best way to do that is have someone with a "power purge" come out and run all the air out of the system. If you are not having any serious issues steering the boat by hand, then I am not sure I buy the air theory. I think it is something else. While the NP500 is about 20 years old, it is a very good pilot.

1) Check the back of your control heads. There are two connections. They should either have two cables connected or a cable and a terminator. There should be no open connection or dust cap.
2) When you run the rudder test and it fails it will say why it fails. Exactly what does it say when it fails?

 

[Brad Allan]

Thanks for your reply Johnny. Next time I'm at the boat I'll run the test again and give you that info. I don't know if this is of any help in diagnosing: I tried to do a sea calibration (manual mode because it wouldn't steer the boat to port in automatic), and part way through the process, the message "rudder drive error" came up.

 

[Johnny Electron]

My guess is the rudder reference unit has worn out and it can't sense the rudder is moving properly. Try checking the RRU using this document.

 

[Brad Allan]

Thanks, I'll do that. However, it appears that the RRU is working properly because the rudder position indication on both autopilot head units looks to be accurate and consistent in both directions.