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Old 25-08-2009, 14:04   #1
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Autohelm 4000 Intermittently Dives Port or Starboard

I have a 1995 vintage Autohelm 4000 which occasionally makes a rather extreme course correction (20-30 degrees) and gradually returns to its original heading. Usually I disconnect it and reset the course before it resets.

I have Raytheon wind direction/speed/depth/VMG/multi instruments and a ST600R remote on the Seatalk line as well as a fluxgate compass hooked to the autopilot via the NMEA connections.

With all electronics except the autopilot turned off, it still does this.
It happens intermittently every ten minutes or so with no apparent pattern or reason such as big waves etc.

Any ideas appreciated.

Steve B.
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Old 25-08-2009, 18:22   #2
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Sounds like a PCB (brain) fault. Possible periodical interference from some equipment?

Go thru the menus and see if all is set up properly. Go thru the 'learning' procedure. Check the rudder reference (if fitted). Visually check compass indication when in stand-by - is it 'smooth'.

If this does not help - you may be forced to pass it on to the service point.

b.
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Old 25-08-2009, 19:06   #3
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Rule out the dumb stuf first. Isolate the fluxgate and make sure there is nothing screwing it up. I had a boat that realy had nothing, but the fluxgate thought otherwise.Rudder is next that being bad screwwed my ST 7000. The fluxgate works on 90 degreee quardarnts so test each 90 degrees to be sure there is no intterference. If you take it off it's mounting you cn manually test it in the slip. Lookmofr erros when making the transition from each.

A little raymarine trick is a bearing of 384 means you have none unless it it is really the one that is. It is what they output when they fluxgate goes belly up.
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Old 25-09-2009, 10:16   #4
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I finally found the problem. The four power transistors which drive the motor are mounted on heat sinks on the circuit board,. The problem is that they have short, straight thick leads which have no bends before going thru the circuit board. Due to normal heating the expansion slowly cracks the solder connections. Even though the cracks are so miniscule they're almost invisible, it's enough to cause intermittent operation. I soldered up all of them after looking under high magnification. Out of 12 connections (3 on each of 4 transistors) there were NINE bad connections!

We just got back from a 3 day sail and what a difference! It's just like new, and doesn't correct nearly as much as before, but it keeps a PERFECT course.

If anyone's interested, one of these days I'll take it apart again and post pictures of the offending spots.

Steve B.
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Old 25-09-2009, 12:08   #5
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Quote:
Originally Posted by senormechanico View Post
I finally found the problem.
Steve B.
Thanks for letting us know.

I have not replaced items that I found cold solder joints on too though most would not/could not go that far I suspect.

Congrats!
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Old 04-10-2009, 04:56   #6
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How see?

Did you just use a good magnifying glass? I'm impressed you thought of examining them so closely and it paid off....
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Old 04-10-2009, 11:41   #7
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You need a workbench (chart table?) with LOTS of light, a magnifying
glass, and a soldering pencil.

Good magnification will allow you to see the cracks, but there's nothing wrong with soldering connections of the four power transistor and reinstalling it to try out the fix. It's a shotgun approach, but I'll bet if you have the same symptoms, it'll fix it. Don't be afraid of giving it a try if you're halfway decent with a soldering iron. If you're not sure, get a friend who can solder. I doubt there's any significant risk of static damage.

Steve B.
(retired electronics tech)
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Old 27-10-2009, 18:12   #8
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Steve B. Did you ever get your answer?

I've seen this very behavior on a C34 and we traced it down to a vibration effect on the flux gate compass head. The internal gimgal locks up due to a harmonic effect and tracks off course until condition change enough to free it and the electrons goes oops and get you back on track.

I've only seen it under power and if I remember correctly it recovered right away if you throttled back. The cure is to move it or get it isolated on a vibration damping mat.
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Old 27-10-2009, 19:59   #9
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It was bad solder connections behind the display on the circuit board where the four power transistors (which drive the steering motor) are located.

I emailed Richard Spindler at Latitude 38 as he had the same problem with his Raytheon autopilot. His had the same problem (and I suspect the same fix), but I haven't heard back from him.

Steve B.
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Old 08-11-2009, 22:17   #10
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Seniormechanico....well knock me down, I've just bought a boat and the autohelm (similar vintage and same make) does the same thing - suddenly dives off to port. I'll go through your routine and see how I go. Thank you.
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