Autohelm depth sounder fault

[miket]

I have an Autohelm depth sounder (approx' year 2000) not combined with speed, and it has recently been playing up;
1. The measure of depth "Metres" flashes indicating an unreliable reading.
2. It shows a depth but that does not change until the unit is switched off. The next reading may be different but then again remains unchanged until the next switch off.

Anyone had these symptoms and was there a resolution?
Can I take the upper unit (display) for testing anywhere?
Can one replace the transducer (hull end) and retain the display? I have a matching Log!!

The handbook is not very helpful. It declares that if "metres" flashes the reading is unreliable!! I got that far without the handbook!
Thanks all.

Also on Practical Boat Owner site

 

[aquatom]

What type of transducer do you have? If you have an internal type then it may be low on oil....

 

[miket]

Internal?

Year 2000 Broom 38CL.
I believe it is internal.
How does one go about checking/ topping up?

 

[aquatom]

If it is an internal type then it should be a 10cm diameter round black unit glued to the inside of the hull.

If so then turn it 1/4 of a turn anticlockwise and lift it off. The black plastic ring should stay connected to the hull. Top up with sunflower oil and refit.

That's if it is an internal type.....