Seabotix have been great and should have been my first point of contact. Apologies to the team at Seabotix.
Just for the record, the top-side board FSK was replaced a while ago and since then I’ve had problems tuning-in my sonar comms, mainly as I didn’t have access to a scope and wasn’t sure on the test points. Hence the post.
The tuning is pretty fiddly, but there is a new version of the board that eliminates the need for the tuning.
Thanks to Seth and the team for their support and information received. 😀