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

HenryD said:

My autopilot, a Robertson/Simrad AP20 is displaying an error - Compass Data Missing.

Click to expand...

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?

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.

I tried a calibration and the compass does not seem to be responding.
Larry, a PM on way.

Our AP 20 course computer power board is what was/is affecting ours. Compass OK.

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.

JDCAVE said:

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.

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Maybe the rudder position arm is loose. Assume the alarm is real until proven false. Time for an inspection.

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. I’ll check it over with my go to fellow on this stuff.

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.

High Wire said:

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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Ahhhh! 2 cables top left of photo?

Sensor is behind the blue "box". Can't really see it.
Should look something like this:

https://www.hodgesmarine.com/Simrad...lkid=IqLz5ZcfiCe5&ppcsu=xhg7f5djqeniramsegdoh

What is that spring hatch holder with the pulled out screws doing there?

It’s not a hatch holder. It’s 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 I’ve not opened it up. There is a rudder position display above the helm and is probably separate from the AP. It’s connected to something inside the blue box. All installations predate my involvement.it will be another learning experience.

You can use any heading sensor you might have on your “network”

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

High Wire said:

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.

Click to expand...

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, my AP-20 is getting worse. I’m going to have to deal with it. I’ll try the rudder sensor, but if it gets beyond that, I’ll have to rethink how else to approach it. I’m not inclined to chase my tail for too long.

Jim: Bummer. Here’s 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.

Larry M said:

...Here’s what our KK42 looks like.

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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.

wkearney99 said:

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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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.

wkearney99 said:

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!

Click to expand...

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.

High Wire said:

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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And pick up some wire lube for pulling the new one. It makes a HUGE difference!

High Wire said:

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.

Click to expand...

Maerin said:

And pick up some wire lube for pulling the new one. It makes a HUGE difference!

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Wire lube does help when there's a lot in the bundle. Clean up is a bit of a hassle and it leaves gunk to collect dirt.

That and pulling assumes wires not being secured. Very little of the cabling I've encountered on the GB is like that. Quite a lot of it is properly secured, so it's not always a simple pull. Lots of wood panels to remove.

Assuming a proper connection, is there any problem with splicing?

I’m in the middle of nowhere and will lose cell service soon. Would it be possible to determine which of the wires to connect and just cut the cable and reconnect for the new rudder sensor? That would save pulling wires through difficult wire chases. In any event, it will have to be something I do when I return.

That's my question also. Some connections depend on very specific wire lengths (impedance, capacitance, etc). Others only care about min/max lengths, shielding and proper pair twists. The big challenge is in making sure to maintain the same water-resistant setup as an un-spliced cable.

Take the new rudder sensor to the junction box and hook it up to the sensor terminals. hand sweep it back and forth and watch display and see that rudder position responds.

If so, good. Then go back to rudder and cut the old cable, strip it back and splice each lead and shield even if crudely. Repeat same test. If it works, install it and then you can drag the cable at a convenient time.

I’ve replaced the rudder sensor with the exact some one, however the supplied and attached cable was of insufficient length, so I spliced it to the existing cable, after it was pulled into the engine room which is a much drier space. Used butt connectors and heat shrink. It shows the rudder angle at the AP display, so working at least as well as the old one. There is less “play” in the new “rod assembly” to the rudder. We shall see how this works.

Finally tested this solution today on a 28 nm trip from Steveston to Lions Bay. Moderately sloppy beam sea. Seemed to work well the entire trip with no error messages.

Jim

HenryD said:

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

Click to expand...

Wow, this thread really went off the rails.

If anyone is looking for the above "Compass Data Missing" error, I had the same problem with an AP21, J300X and RFC35R rate compass. I checked the voltage and read ~24 volts on the Grey and Pink wires. Continuity was good from the robnet White and Brown wires from the compass to the J300X, measuring 0 ohms resistance. I ended up replacing the compass with a used RC25. I was worried about the different voltage ratings on the compasses since my boat is 12V, but it all worked out.

Hope to get the boat out to do a recalibration soon.

Since I posted over two years ago another AP gremlin popped up saying "rudder indicator error." A friend and top flight instrument guy said to remove and clean carbon from the pump motor brushes. Problem solved, for now anyway.