bizarre problem with autohelm

[alex23299]

Grateful for any views on this.
My trusty Raymarine autohelm ST4000, belt-driven to a wheel, now decides to turn hard to port when you switch it on. It then stabilises for a second and then turns left again. It does it in any conditions, under motor or sail. I've checked for metal near the compass. There have been no significant changes to the boat since last season, when it worked. I've tried resetting everything, and now gone back to defaults - no change. The compass seems to be reading OK. Connections look ok, though I haven't yet tested the resistance.

Raymarine tell me I may need a new fluxgate compass, or I may need to fit a rudder sensor - but I've never had one before, so why now?

Ideas? Thanks

 

[Topcat47]

I had a similar problem with my original Autohelm 2000 some years ago. The fluxgate compass has slipped off it's gimbals. I don't know if the modern ones are solid state, but my old one just had coils and magnets. It's worth a look, I'd have thought

 

[seamaster30]

Not sure how your system works, but here is my experience that may help...
I have just repaired my old Cetrek autopilot, which was doing exactly the same thing. - The rudder indicator uses two bulbs and sensors with a rotating disc that covers/uncovers them.
One of the bulbs had blown. - Do you have an indicator gauge on the system? - Mine showed the rudder as hard over, which it was not.
I actually replaced the bulbs with LED's (and a suitable adjustment to the resistors) and all is well again.

 

[alex23299]

Good thought but it is solid state, not gyro... I think. I've had it off but not got inside it...
thanks
a

 

[whipper_snapper]

Does it show the correct heading when in standby mode? If so it can't be a compass fault, if not it is probably a compass fault.

 

[Crewlink]

You shouldn't need a part that was not on the system to make it work.

 

[Piddy]

I had something similar a few years ago. I had to change the output transistors as one had gone duff.

Sorry, can't remember much more that that as it was 7 - 8 years ago.

Cheers

 

[alex23299]

thanks - was the output transistor in the fluxgate compass? - I'm thinking of replacing that...

 

[shaunksb]

Just had exactly same problem with my ST4000+. Diagnosed as faulty PCB board (water damaged through minute leak in casing). Replaced and now working but parts hard to get. I used firm from ebay advertising fixed priced repairs.