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[Terry]

One for the Techies. I have an old Robbe Sirius yacht, really enjoy sailing it. The sail winch has become very erratic, hunting for the input from the Tx and being generally unreliable. i have tried a different Tx, same problem. The rudder servo works fine so I guess the Rx is OK The amount of travel is adjustable via a "pot" (the small blue piece in th photo). So I thought check the tracks on the potentiometer and clean them, that Is how old I am !! When I opened the case I was confronted with this small blue component, so no work that I can do there. Looking at the other photo a component, longer than the motor can be seen, I have no idea what that is.
Question. Can someone please explain how this all works, and do you think it is possible to be repaired. Buying a new servo is not an option.


Thanks, Terry.


https://postimg.cc/7f6y5V6F
https://postimg.cc/vgMJb7kS

[HMS Invisible]

 I've repaired sailwinch servos of different types and I am not yet convinced from your description that your servo is faulty.
 Tell us if it is a multi-turn drum servo and, when you last used it out of the water?

I expect a drum type sailwinch to overshoot without a sail load to pull against.
There will be a feedback pot attached to the servo's output shaft, either directly or by a reduction gearing in the case of the dirt cheap sailwinches.

Have you seen kingmaxhobby website?
In advance of you sorting image attachments, try Postimg or say what filesize is the photo.

[Terry]

Thanks for the reply. It is a multi turn drum servo. the problem arose when checking the boat over before going to the lake. It was  always necessary to give it a bit of "exercise", just a few rotations back and forth, then it was fine and never overshot with no load. Pictures now available in my first msg.

[JimG]

The object longer than the motor will be a multi turn pot connected to the output shaft to allow the winch to have more than the normal servo movement. The blue object looks like a trim pot, probably sealed. If they are faulty you could try a search to see if they are still available, if so they could be replaced although whether that would be worth it is debateable.
Jim

[HMS Invisible]

Thanks for the reply. It is a multi turn drum servo. the problem arose when checking the boat over before going to the lake. It was  always necessary to give it a bit of "exercise", just a few rotations back and forth, then it was fine and never overshot with no load. Pictures now available in my first msg.

You said erratic and I expect a drum servo set to 4 turns to overshoot then oscillate without the dampening reduced by the lack of mechanical resistance. I expect it to oscillate ten times greater in angle than does a high stall, unloaded quarter turn servo with the same timing component values.
 This is what I mean by overshoot. link
It would possibly take a video to convince me it has a faulty pot without you doing a resistance meter check on the pot.
You just measure resistance of the pot wiper to one end as you physically turn over it's range. I've done this, replaced pots and motors, and a fault in the pot is obvious in a resistance test.

[roycv]

Hi all I agree with Jim post #3 the giveaway is 4K7 which indicates a 4700 ohm potentiometer.  The blue cube is probably a trim pot, if so there should be a tiny screw head protruding from an edge where a screwdriver can make an adjustment.
Is this to adjust the neutral position?

I have a similar problem with a very old sail servo circa 1966 from Fleet.  It always hunted, although the proprietor of Fleet denied it and said it was traffic noise!  Would not replace it either, back then it was a very expensive unit. 
I tried pot cleaning to no avail so stopped using it.
My one is bright red has a double drum and I think sourced from South Africa!
Thinking off-piste could it be the motor needs some more RFI capacitors?
Possibly the dead-band is too narrow?
Roy

[HMS Invisible]

I think the first task is to identify the wiper terminal on the feedback pot and measure the resistance as it is slowly wound.