Seafarer echo sounder - 'ring of fire' issue

[SailB]

Hi All,

I have a Seafarer 5 echo sounder with digital cockpit repeater which is much loved, but has recently developed a malfunction. The repeater went first, showing simply the number of times I had switched the unit on and off attempting to coax it into showing the depth while downstairs the spinning dot worked fine. Now that too has failed, just lighting up all the way round like a 'ring of fire'.

Anyone have an idea what might have gone wrong and how to rectify it?

I have checked the transducer, it has enough oil and the clicks are audible when held to the ear, so that seems to be working. There are no external obstructions on the hull either.

I know it's ancient technology, and we could just replace it with a NASA unit relatively inexpensively, but it would be nice to keep it too!

Thanks for any suggestions!

 

[Rum Run]

try opening the case of the main unit and looking for corrosion on the circuit board. If you find any it may be repairable since all the components will be quite big and the tracks obvious unlike modern surface mount products.

 

[JumbleDuck]

try opening the case of the main unit and looking for corrosion on the circuit board. If you find any it may be repairable since all the components will be quite big and the tracks obvious unlike modern surface mount products.

+1. As far as I know, the LED simply shows an amplified version of what the transducer picks up, so noise in the system - from a bad connection, for example - may show up as a red ring.

I'd also suggest trying a new (or fresh) transducer.

 

[Ian_Edwards]

If the LED (s) are light all the time (ring of fire) then the first thing I'd check is the connections to the transducer (particularly the earth or screen). The signal returned from the transducer is very small and requires a high gain amplifier, often with time varied gain, i.e. the gain of the amplifier increases with range (depth). Any noise getting into the input side of the amplifier will simple saturate the output and trigger the LEDs.
I don't know if you have a circuit diagram, but if you have, then using a multimeter, or better an oscilloscope, you could try to trace the fault.
This is a generic description, I can't find a circuit diagram online.
The next step would be to check the output of the amplifier, operating in air that shouldn't have any signal on it, i.e. read around 0 volts (or it could be sitting at half the supply voltage ~6volts depending on how it is coupled)
If it's sitting at the supply voltage, +12v? Then the amplifier is knackered.
I'd then expect the output to go through some form of rectifier, or envelope detector, to get rid of the carrier frequency, typically 150kHz, followed by discriminator, a device which will provide an output when the input exceeds a reference voltage, usually the reference voltage is variable and is part of the gain control. The output of the discriminator should be around 0 volts, if not then there is problem between the main amplifier and the output of the discriminator.
The next part of the circuit will probably be a driver for the LED(s). The output of this device will almost certainly be "on", at the voltage required by the LED(s), because they are permanently on. If the output from the LED driver is at 0 volts, then the problem is likely to be mechanism between the driver and the display. I don't know if the mark 5 still has a rotating arm, if it does then check all the connection around comutator. However since you said the digital display out lasted the ring, I would expect that the problem is either a poor connection from the transducer or in the amplifier.

I hope this helps, it's hard to provide advice remotely, without a circuit diagram. However, these are very simple devices built from discrete components, and are quite easy to fault find if you have a circuit diagram and someone who has, and can drive an oscilloscope. Sourcing replacement components may be difficult, given the age of the device.

 

[James_Calvert]

Hi.

I have an old Seafarer of similar vintage. I think the light on the rotating arm is neon isn't it, rather than led?

No idea if it makes any difference to the amazingly clear advice above, but just thought I'd mention it.

 

[Ian_Edwards]

I know the early Seafarers where Neon, I'd assumed, perhaps in correctly, that the Mark 5 had updated to an LED, if I'm not correct then much of what I've possed is still correct, but instead of having a n LED driver on the output of the amplifier, there will be some circuitry to drive the neon display.
As said it's a generic description of an echo sounder, without a circuit diagram it's difficult to be more specific.
In the 1970's and early 80's I designed and built experimental echosounders, and operated them on research vessels, so I have a good idea they work, although I have undoubtedly forgotten much of what I knew over the years.

 

[andsarkit]

Somewhere in the shed I have a little test box that provides a variable delay on the return signal. I haven't used it for years but found it quite useful to check if the fault was in the transducer or display. If you are anywhere near Devon you are welcome to borrow it or I also have a spare transducer you could try.

 

[Poecheng]

If your problem lies in the Seafarer display unit, I have a 700 model that you are welcome to have - just checked in the garage and exactly where I thought it was !

 

[SailB]

Thank you all for this invaluable information! Makes sense that the ring of fire is caused by noise in the system, so I'll go on a good search with the multimeter assisted by your notes! We've only had the boat a couple of months and are working our way though her idiosyncrasies!

I think the cockpit repeater may have had it though, not only because it's not working, but because there is so much water in it it's impossible to see! Not a good situation for such a vital instrument!

 

[SailB]

If your problem lies in the Seafarer display unit, I have a 700 model that you are welcome to have - just checked in the garage and exactly where I thought it was !

Many thanks for your generous offer! The boat is on the east coast so we'll see what comes of my investigations!