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Old 03-03-2018, 11:19 AM   #1
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Robertson / Simrad AP20 error

Hello,
My autopilot, a Robertson/Simrad AP20 is displaying an error - Compass Data Missing. I checked the connections at the J300X. The RFC35 compass does not have any indicators on it.
Is there a way to troubleshoot it?
I see in the manual the AP20 can use an alternative NEMA compass - any suggestions that would work?

Thanks
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Old 03-03-2018, 12:02 PM   #2
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My autopilot, a Robertson/Simrad AP20 is displaying an error - Compass Data Missing.
Two years ago we suffered a "Rudder Indicator" data failure on our AP20. Pulled all the wires, lubed them still no go. All expert advice was to change out the rudder indicator, we did, and still a failure popped up.

Then we changed to a new power source, voila, found a low voltage issue. Weak power board was suggested but spare parts tough to find for that unit. Problem hopefully solved with different 12 V source.. But, given our long distance cruising style and liking redundancy, a new Furuno AP system was installed with the AP20 remaining as backup. Glad we did it as new AP is much better than the old AP20 on its best days.

Does your compass feed an MFD as well? One more thing, have you tried a master reset, turning the vessel through about 720 degrees slowly as described in the Simrad book?
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Old 03-03-2018, 02:41 PM   #3
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If you can find one, definitely upgrade to a Simrad RC25 Rate Compass. It replaced the earlier RFC35R Rate Compass. The autopilot performance will be GREATLY improved. From the brochure "The Simrad RC25 Rate Compass is used with AP35 and AP50 (Robnet). Fluxgate compass with integrated rate of turn sensor. Utilizes a solid state rate sensor and a magnetic fluxgate sensor. Provides a dramatic improvement to the dynamic performance of both the autopilot and a stabilized radar display." They are designed to work with any J300X based system. Here is a chart that shows the difference in output between Fluxgate and Rate Compasses.


Alternatively, the original basic RFC35 Fluxgate Compass can often be had on eBay for around $250 or so.

OK, I actually have both for sale, but the RC25 is part of a complete AP22/J300X/RC25/FU50/RPU80 autopilot package I plan to list on eBay. The RFC35 Fluxgate Compass is a working spare I removed when upgrading to the RC25 Rate Compass. You can PM me if you think you might need it.

Hope I didn't break any TF rules with that.
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Old 03-04-2018, 10:50 PM   #4
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I tried a calibration and the compass does not seem to be responding.
Larry, a PM on way.
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Old 03-04-2018, 10:57 PM   #5
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Our AP 20 course computer power board is what was/is affecting ours. Compass OK.
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Old 03-12-2018, 06:31 PM   #6
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My AP 20 may also be on its way out. An alarm goes off that indicates ďRudder not respondingĒ. It happened again today and I powered it down for a few minutes and restarted and it worked fine for the rest of the trip. Iím going to check hydraulic fluid levels, etc, but I might be looking at a replacement, probably Furuno.
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Old 03-12-2018, 06:40 PM   #7
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My AP 20 may also be on its way out. An alarm goes off that indicates “Rudder not responding”. It happened again today and I powered it down for a few minutes and restarted and it worked fine for the rest of the trip. I’m going to check hydraulic fluid levels, etc, but I might be looking at a replacement, probably Furuno.
Maybe the rudder position arm is loose. Assume the alarm is real until proven false. Time for an inspection.
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Old 03-12-2018, 08:00 PM   #8
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I had a look back there when the alarm went off while underway and everything looked ok. Nothing evident to me. She handles fine while on the wheel. Iíll check it over with my go to fellow on this stuff.
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Old 03-12-2018, 08:16 PM   #9
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My friends Simrad AP rudder position sensor had a dead spot and I believe would get the same alarm. Its just a wiper contact like a fuel lever sensor. Worn out and no longer sees the rudder movement. Easy fix but a PITA to run the cable.
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Old 03-12-2018, 08:28 PM   #10
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Robertson / Simrad AP20 error

Quote:
Originally Posted by High Wire View Post
My friends Simrad AP rudder position sensor had a dead spot and I believe would get the same alarm. Its just a wiper contact like a fuel lever sensor. Worn out and no longer sees the rudder movement. Easy fix but a PITA to run the cable.

Ahhhh! 2 cables top left of photo?

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Old 03-12-2018, 08:58 PM   #11
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Sensor is behind the blue "box". Can't really see it.
Should look something like this:

https://www.hodgesmarine.com/Simrad-...jqeniramsegdoh

What is that spring hatch holder with the pulled out screws doing there?
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Old 03-12-2018, 09:36 PM   #12
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Robertson / Simrad AP20 error

Itís not a hatch holder. Itís connected to the rudder assembly. I wonder if it is part a separate rudder position sensor, separate from the AP. The box protects everything there and Iíve not opened it up. There is a rudder position display above the helm and is probably separate from the AP. Itís connected to something inside the blue box. All installations predate my involvement.it will be another learning experience.
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Old 03-13-2018, 12:03 AM   #13
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You can use any heading sensor you might have on your ďnetworkĒ

I tend to use my Furuno heading sensor, since it is what the radar uses to determine target bearing.

The root cause of your missing dats is simpley that your heading sensor Mag Compass is not outputting daya over the NMEA link to your autopilot computer
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Old 05-01-2018, 12:45 PM   #14
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Quote:
Originally Posted by High Wire View Post
My friends Simrad AP rudder position sensor had a dead spot and I believe would get the same alarm. Its just a wiper contact like a fuel lever sensor. Worn out and no longer sees the rudder movement. Easy fix but a PITA to run the cable.
Easy fix being the wiper inside or replacement of the whole sensor and it's cable all the way back to the autopilot computer? Re-running the cable would be tedious, for sure!
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Old 05-01-2018, 02:09 PM   #15
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Yes, my AP-20 is getting worse. Iím going to have to deal with it. Iíll try the rudder sensor, but if it gets beyond that, Iíll have to rethink how else to approach it. Iím not inclined to chase my tail for too long.
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Old 05-01-2018, 02:41 PM   #16
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Jim: Bummer. Hereís what our KK42 looks like. The small center one with the spring is VDO rudder indicator that you probably have over the helm. The one on the right is for our Simrad AP which is identical to the Robertson AP20 other than the name. When we replaced our Robertson with the Simrad, I kept the Robertson for a backup. It only has two wires and goes to the control box/computer and easy to trace out.
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Old 05-01-2018, 03:06 PM   #17
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...Hereís what our KK42 looks like.
Looks like the same setup as in my GB EB47. A VDO/Siemens analog rudder indicator for the analog gauge at the helm and an RF300 for the autopilot.
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Old 05-01-2018, 03:25 PM   #18
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Looks like the same setup as in my GB EB47. A VDO/Siemens analog rudder indicator for the analog gauge at the helm and an RF300 for the autopilot.
The RF300s are pretty bullet proof for the most from what I’ve been told. But if someone needs one, I just looked on EBay and there are a bunch listed for ~ $80 US.
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Old 05-01-2018, 07:41 PM   #19
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Easy fix being the wiper inside or replacement of the whole sensor and it's cable all the way back to the autopilot computer? Re-running the cable would be tedious, for sure!
Yes. Replace the whole sensor. When you pull out the old cable, first tape on 1/8" nylon cord and pull it through to the stern. Then tape on new cable and pull that back through from stern to helm. Much easier job with 2 people.
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Old 05-01-2018, 09:30 PM   #20
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Yes. Replace the whole sensor. When you pull out the old cable, first tape on 1/8" nylon cord and pull it through to the stern. Then tape on new cable and pull that back through from stern to helm. Much easier job with 2 people.
And pick up some wire lube for pulling the new one. It makes a HUGE difference!
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