Bidata ST30 problem

MM5AHO

MM5AHO

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I had a working ST30 last year to start with, then the speed started to fail. As the face was quite crazed, I bought a replacement instrument, thinking to connect the existing hull units to it.
The speed now works fine but the depth doesn't.
The depth shows 0.0 with the word "metres" flashing. The book says this is "loss of signal" - the depth signal is lost. But its doing this at any depth.
The digits are not flashing (which the books says means transducer or cable fault.)

Any ideas, or sources of info on these ?
 
Update
The connections checked out fine, but thanks for that.
Yes the speed transducer and depth instrument do have seperate cables.

Reading on various forums found one bit of useful advice: listen on an AM radio for the clicks. Do this near the instrument, and also at the display.
Today we put the old unit back in and it reads depth fine.
This suggests the display unit is the problem.
Putting this on the workbench and adding a suitable load impedance, the output of the head unit is very good. )This was suggested by the radio signal using a small transistor radio)
So the issue seem to be the display unit (which generates the signal also) is not reading the echo sent back from the transducer.
The display unit was "new old stock", not used before.

Continuing the investigation.
 
Find someone locally with a working ST30 unit and swap them?

Is yours a combined sensor, with depth, speed and temperature in one removable unit? It will be an Airmar unit, which you can buy direct if that's the eventual conclusion.

Our depth has also gone, but I think that is related to old age and we have already updated when we invested in a new Navico chart plotter. Ours is a separate depth unit, bonded in - and I've simply left it in situ.

Post how you get on, good luck

Jonathan
 
Swapping the old unit (that we'd removed) back in, and the depth works OK. That seems to confirm that the transducers are OK. (echo sounder and paddlewheel speed type - there's no temp on these older ones).
Opening up the new one on the bench (my son doing this, he is better at it than me!), he discovered a fried diode - surface mount type - on the board. This is in the receive part of the board, so perhaps explains the non - receipt of the echo and hence zero display.
So a replacement diode put in there or similar value, and next trip will swap the "new" unit in and see if that's fixed it.
 
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