Does anyone have a Navman Fishfinder

[Major Catastrophe]

Navman Fish 4150sx or similar Navman fishfinder and based in North Wales so that I can try my base unit connected to your transponder, or your base unit on my transponder so that I can track down whether it is the unit or the transponder at fault.

The sympton is that the display keeps jumping between 0.nn and the true depth as in these pictures.

You can see the frequency of the jumps in the lines on the depth image under the boat.

I have tried and tested the earthing, as suggested by another forumite, but now need to isolate the problem to the unit or the wiring/transponder.

 

[RobWales]

Looks like you have an interupt in the signal from the transducer,normal cause is air bubbles below the receiving face causing lack of feedback pulse!
Make sure you have the position set correct.
Where on your hull is it placed?

 

[Major Catastrophe]

It is transom mounted.

It worked fine for two seasons and when I put it back in the water this year, it doesn't work fine.

It is set at the same angle as before....in fact it has never been touched.

 

[RobWales]

Well gotta say its a classic symptom of air below the transducer!
Even one little barnacle on the underside of the transducer or even the hull infront of the ducer can and will interupt the flow over the unit causing that problem.
It has happened to me in the past.
My money is on that!
Bet it does not occur when your stationary?

 

[Major Catastrophe]

[ QUOTE ]
Bet it does not occur when your stationary?

[/ QUOTE ]

Wrong, I'm afraid.

Since the problem started it just shows two bars when I switch on, like this -.- until it 'warms' up, then it will show some random depths, even got 48 metres under my keel once, but I was still in my berth, then it settles down to flicking between the correct depth and the 0 point something depth as in the second picture.

 

[RobWales]

Well I stand corrected!
OH well good luck with your quest to solve.
Cheers

 

[Major Catastrophe]

Thanks for the suggestions, though. If I can isolate the problem to either the unit or the transponder, then I can start to solve it.

I will have to go knocking on doors in the marina to see if I can find anyone with a Navman Fish.