B&G Sonic Speed failure


David Crisp
 

Hi All,

The sonic speed on Wilna Grace has not worked for sometime so with the wisdom learned from this group I've been investigating.  Adjusting the spacing knob on the processing unit I'm unable to get the red light to come on. 
I have disconnected the transducer cables and tested them and all seems okay: - 111.4kΩ on one transducer and 111.7kΩ on the other which seems in tolerance and infinite resistance between all cables and the shielding.  Any advice on what I should check next?

David Crisp
SV Wilna Grace
Amel 54 #58


Stefan Jeukendrup
 

Hi David,


Looks like  you found the document: https://amelyachtowners.groups.io/g/main/files/B%20&%20G%20Sonic%20Speed%20Information/SonicSpeedTroubleshooting.pdf

The red led not working means that somewhere in the "loop" there is a problem: (transmitter on Sonic speed board, transmit sensor, ultrasonic waves through the water, receive sensor, phased lock loop, Automatic Gain Control amplifier)

I guess you measured the internal power supply already, but did you measure AGC, is it between 1.8 and 2.5V?


Most likely  causes:

* something in the water path between the 2 crystals ( and that includes fouling and loose rubber caps although unlikely since your resistor values are good)

 * defecitive board, test by swapping with another one.

I have several Sonic speed boards if you need one to test.

Hope this is helpfull in some way.


Stefan Jeukendrup

sv Malaka Queen

SM2k #348 @ Newry Northern Ireland


Op 10-10-2021 om 10:30 schreef David Crisp:

Hi All,

The sonic speed on Wilna Grace has not worked for sometime so with the wisdom learned from this group I've been investigating.  Adjusting the spacing knob on the processing unit I'm unable to get the red light to come on. 
I have disconnected the transducer cables and tested them and all seems okay: - 111.4kΩ on one transducer and 111.7kΩ on the other which seems in tolerance and infinite resistance between all cables and the shielding.  Any advice on what I should check next?

David Crisp
SV Wilna Grace
Amel 54 #58


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


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


David Crisp
 

Hi Stefan,

Had already bought replacement transducers from Maxmarine and was planning to install them but halted that project when the existing ones checked out okay at 111kΩ and so I started suspecting the PCB.  I'll try filling the transducer recess in the hull with silicon (to replace the missing neoprene cap) as you suggest then test with a water filled pipe.  If the AGC voltage checks out okay and I still can't get the system working I'll replace the transducers.

With regards replacing the transducers:  I've tried to find where the cables enter the boat but so far without success.  When replacing the transducers, do you attached a pull through at the electronics box under the saloon seat and pull it through from there as you extract the old transducers or is there some other access point for the transducer cables one works from?  As I understand the transducer cables enter above the waterline so the transducers should not be sealed in their tubes.

With thanks,
--
David Crisp
SV Wilna Grace
Amel 54 #58