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Raymarine forum - [TG11] Fluxgate compass / course computer troubleshooting

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My system includes an E12091 S2G AST course computer with a connected M81190 fluxgate compass. During last season from time to time the heading information would be shown incorrectly. I would reset this via the sea trial wizard either manually or via COG which would resolve it temporarily.

When relaunching this season the same issue appeared but on a much more regular basis and the "reset" would only resolve the problem for a very short time, in some cases as soon as the boat changed heading. I replaced the fluxgate compass with one that tested OK per the following procedure (The old one I removed tested on the lower size of all the resistance targets but still within tolerance.) Location is the same as the old one (where installed by the OEM) and the new compass swing test netted just 2 deg variation.

With the new fluxgate compass installed I again manually had to reset to the proper heading. The proper heading held and reflected the correct boat heading throughout about a 6 hr sail. However, every time the power is cycled the heading has to be reset manually again to the correct heading.

Nothing has been changed in the wiring between the compass and the course computer. All other autopilot functions seem to work perfectly. Does that leave the course computer as the only likely problem? Any other troubleshooting steps I need can try before I either replace the E12091 with a used one from ebay or change the whole system out to the newer EV1/ACU200?

Trying to avoid just replacing things if there is some setting or other solution I should be checking first.


Hello Tony,

In what way is the heading wrong? Does it:

  1. seem to respond normally as you turn and give heading values that look correct except that the heading appears rotated? This would probably indicate that the course computer's EEPROM non-volatile memory were no longer storing the calibration offset. This can't be repaired but the pragmatic workaround would be to fabricate a bracket to rotate the fluxgate into the correct orientation. Or replace the pilot...
  2. lag as you turn the boat, or drift when not turning? If this is not related to specific headings but occurs all the way through 360 degrees then it's likely a failed Rate Gyro. Does the problem go away if you remove the grey plastic cover and unplug the 3-pin white rate-gyro connector half-way up the left-hand edge of the board (do this when powered off)? This would revert it from S2G to standard S2 and would get you going again with reduced steering performance. The replacement gyros were a spare but probably aren't economic to try to source now.
  3. appear to indicate correctly through part of the turn or at some times or in some directions and then not in others? This usually indicates a fluxgate problem still. Fluxgate broken windings can be frustratingly intermittent and I always treat 'pass' measurements with suspicion: I sea-trialled a boat in Turkey once, 3 days in a row, and only on the third day did the long-running intermittent problem show up.

If you can describe the heading problem more explicitly then I can probably give you a more concrete diagnosis.

Thanks Tom. Here is a bit more on the heading problem.

1) Last season - original fluxgate - problem seemed more along the lines of "a" in your reply. Typically about 180 deg or so off, both the position of the boat on the MFD and the actual heading read-out. I would reset manually or via COG and all would function fine for a period of time. I'd say I reset about 3 or 4 times over the course of 6 months.

2) Early this season - original fluxgate - same issue as #1 but occurred every time I would power on the electronics. Even after resetting manually t would show an incorrect heading/boat position pretty much as soon as I changed the direction of the boat. Hard to say if this was somewhat like "b" because there did not seem to be any consistent lag. That being said, I would say that when trying to re-swing I would almost always would get a "turn to fast" at the same exact heading on each turn attempt. Seeing I was using the wheel lock and changed nothing else I eventually realized this was not likely being caused by by actual turn rate but by something else. (Also did this at two different locations to make sure there was not a current or something else changing my speed/turn rate.) Next step was to replace the fluxgate.

3) Now - replacement fluxgate - heading/boat position shows incorrect when powered on. In my slip this seems to come up typically around 290 deg M. I reset manually in the slip to 350 deg M which is my actual magnetic compass heading. The correct heading/boat position holds accurately until the electronics are powered down and then as soon as I power cycle I'm back to 290 deg M or so.

I've not had a chance to try unplugging the 3-pin gyro connector as you mention below. Based on your thoughts it seems more likely though that for some reason my offset is not being stored in the EEPROM, but all other functions of the pilot seem to operate without any issue so not sure if that would be the case of not.

Hopefully this helps give you a better feel for your diagnosis?


Hello Tony,

Good info, thanks. From the sound of it you have two different problems:

  1. a failed EEPROM in your course computer such that it it no longer able to retain heading offset calibrations through a power-cycle.
  2. on your original fluxgate, a broken winding leading to a 'dead sector', which is what was giving the 'too fast' warning at the same point in the compass swing each time.

The EEPROM on the S2G's board can't be replaced and we don't have spares for them any longer, so your options would be either to fabricate a bracket to get the fluxgate into the correct orientation and keep going; find a used T150/T400/S2/S3 or the -G equivalents (T150 was the earlier name for S2, T400 for S3, it's ok to over-rate the course computer to S3, and you could transfer your existing gyro across if you got a non-gyro course-computer) to replace yours, or finally, upgrade to a new Evolution autopilot (EV-200 is the equivalent of S2G.)
I think I'd do a temporary fix by rotating the fluxgate and then budget to upgrade the pilot when you have a chance.

Thanks Tom. Really appreciate the help - trying to diagnose what looks like two separate issues on related equipment was making things difficult.

Temporarily I'll probably just reset the heading to my match my magnetic compass each trip seeing it seems to hold the offset at least until the next time I turn it off/on. I think your idea to budget for an upgrade is for sure the way to go but I have to do some homework to sort out how to extend the SealtalkNG network to the ACU-200 and EV-1 locations. Just a couple of quick follow-ups ...

1) If for some reason I run across a reasonable deal for a replacement older style pilot I noticed there were the S2G AST versions like I have now and also some 150G AST models. It also seems like there are some S2G AST versions with numbers other than E12091 which is what is on my unit. Are there functional differences between S2G and 150G and/or the different S2G "E" numbers?

2) The ACU-200 has a RF Ground connection that from what I can tell was not required on the S2G. Is it crucial that I connect the RF Ground on a new ACU-200 or is it likely that if I have not had interference issues with the S2G I should be OK with the ACU-200 not having this connected assuming I install at the same location? It would just simplify the upgrade based on the current location if this wasn't needed.

Thanks again,

Hello Tony,

Quote:Are there functional differences between S2G and 150G and/or the different S2G "E" numbers?

T150G was the earlier name for S2G, and so is also probably running earlier software. An early T150G could be updated to the latest version of S2 software and then would be essentially indistinguishable (earlier units would have an older but not inferior version of the rate gyro) from an S2G, except that these units probably haven't had the upgrade because it was a somewhat difficult dealer-only upgrade, from a PC using a serial cable.

As far as different part numbers for S2s go: you would have system-pack part numbers and individual course-computer spare part numbers, and then there would be an S2 non-G and S2G part. If you can give me specific part numbers, I can tell you what they are.

Quote:The ACU-200 has a RF Ground connection that from what I can tell was not required on the S2G. Is it crucial that I connect the RF Ground on a new ACU-200 or is it likely that if I have not had interference issues with the S2G I should be OK with the ACU-200 not having this connected assuming I install at the same location?

Correct, the old S2-generation pilots didn't have an RF ground point - I assume the design simply used the supply negative for this purpose. On newer systems we separate RF ground and supply negative in order to allow a dedicated ground point which some vessels have. If you don't have a dedicated RF ground point the normal practice would be to connect the RF ground along with the supply negative - you should use the ground terminal on the ACU, but you can connect this along with the -ve power to make installation easier.

The ACU's installation manual says:
It is important that an effective RF ground is connected to the unit. The unit can be grounded by connecting the drain conductor (screen) to the vessel's RF ground point. On vessels without an RF ground system the drain conductor (screen)
should be connected directly to the negative battery terminal.

The dc power system should be either:
• Negative grounded, with the negative battery terminal connected to the vessel's ground; or
• Floating, with neither battery terminal connected to the vessel's ground.
If several items require grounding, they may first be connected to a single local point (e.g. within a switch panel), with this point connected via a single, appropriately-rated conductor, to the vessel’s common RF ground point.

Hi Tom - sorry to follow-up again but want to be sure I get the RF Ground connection correct with a new ACU-200.

I don't have a dedicated RF ground like a Dynaplate on the boat. There is what I believe is a copper bonding system (see far right in the attached pic) but that seems to be more lightning protection related (this is a sailboat and the copper wiring shown is ultimately connected to a keel bolt). I don't think the thru-hulls are connected to it (will have to check next weekend) and I am nearly certain there are no electronics connected. Seems IMHO best to leave this alone and not potentially introduce any stray currents so ...

What is "-ve" power? I am not familiar with this term.

Assuming this is essentially another term for my 12V DC system, does the drain conductor (screen) need to be a completely separate wire from the ground terminal on the ACU to the negative post of the battery system or can it "pig-tail" from the same negative wire I am using to supply the 12V power to the ACU-200 (#3 on the connections overview in the ACU-200 install manual, page 22)?


Hi Tony,

Sorry that I wasn't clear enough. "-ve" was shorthand for 'negative'. If you bridge across between the ground and supply negative terminals with a large-gauge wire, this should sufficiently satisfy the grounding requirement of the ACU in your instance.

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