problem with DSM30

[aldo]

Hi all. I have a Raymarine C120 display with a GPS 120 and a DSM30+P79 in-hull transducer. Everything was working well until last sunday, when the fishfinder display started not to read the bottom and to show a series of alternate thickness surface bands, but no bottom and no digits. The image is very similar to the picture that some other member published on the forum like the following (this is not my boat, repeat, but the echo image is the same, whatever the bottom and the depth)

I tried many different setup (spped, frequence, power, gain) with no success. I checked, but not very seriously since the sea was very rough and demanding, the connectors and they seemed (repeat, seemed) ok. The transducer installation is perfect, with echography gel inside.

Any suggestion? TIA

[FishinPole2]

Hi Aldo,

You may not have a problem with your equipment.

I have a RayMarine C120 with DSM300 Digital Sounder Module. I can create the exact display you have pictured if I am running too fast. The transducer emits a sound wave which takes some time to hit the bottom and then travel back up to the boat. If my speed is such that the boat has moved past the receiving "cone" of the transducer, the return signal is missed.

Because I usually use auto gain and auto range setting, the system is trying to adjust both in an attempt to display the bottom and depth digits. That's what causes the system to show a series of alternate thickness surface bands, but no bottom and no digits.

Of course speed and depth intereact. If I'm in about 20 fathoms and traveling about 14 knots or faster, I get the exact results shown in your photo. If I reduce speed and/or get into shallower water, system displays properly again.

There might be another problem/explination. What I am describing is repeatable anytime I choose to do so. Everything is in fine working order, just missing the return signal.

Hope this helps you!

Regards,

Stas

aka FishinPole

[ReelAddiction]

Interesting. I have twin C120's and a DSM300 as well. I can run at 36kts and never lose the bottom, nor have I seen that effect on the screen. Maybe something to do with the thru hull? mine is transom mounted.

[aldo]

Thank you all!

I solved the problem that was a combination of factors. The main one was a lack of medium in the transducer case. I'm using echography gel thinking but, for some reason, it losed some volume. I added a little amount of antifreeze fluid and now it works wonderfully, reading a 150' bottom at 25 kts. The secondary problem was that the C120 was set for a P66 instead of P79. I suppose that the C120 lose the correct setup due to the wrong signal due to the bad medium in the case...