Re: B&G Sonic Speed failure

Stefan Jeukendrup

Hi David,

The output is a square wave: 6,25 Hz per Knot boat speed so please measure in Hz.

The AGC pin is marked on the board, measure DC with respect to the ground pin.

I expect your electronic board is still OK => missing rubber cap will most likely be the cause: the hole where the cap was fills up quickly with dirt and that stops the sensor "hearing" the sound waves emitted by the other sensor, even if its resistance still measures "good" ( its just a resistor of 100 kilo-ohm soldered over the crystal)

You say the boat is on the hard now so you can clean and then fill the hole with silicone or neoprene ( with or without the rubber cap). Then test with a tube filled with water between the transducers.

But when you are out on the hard anyhow this is the moment to order and replace  Maxmarine electronics still has them.

Of cause you are very welcome in Newry to test your board.

Hope this helps you,

Stefan Jeukendrup

sv Malaka Queen

SM2k #348 @Newry, Northern Ireland

Op 11-10-2021 om 12:37 schreef David Crisp:

Thanks for the advice Stefan.
Yes I did check there was power going to the unit. I also checked the output to the H2000 and saw 150mV. But, darn it I didn't know to check the AGC voltage, I'll do that after I relaunch in the spring (Preveza, Greece).

The hull was clean although one of the transducers is missing its rubber cap, however reading some B&G documents somewhere I got the impression this doesn't matter. 

I've brought the Sonic speed board back home with me (England) and was thinking either to either get it tested or to source a working spare.  If you have a spare I can borrow/buy I'd be interested.

David Crisp
SV Wilna Grace
Amel 54 #58

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