I checked the sounder yesterday evening and traced the problem to a broken wire on the battery terminal on the negative side. They were all taped up so there would be little chance of it being spotted at sea or with out a tester.
Cables were re-terminated and a new lug fitted, all kit working as expected.
The water looked flat as a pancake and very clear in the channel, very inviting.
I am away next weekend so will bring the boat kit and oxygen up on Monday, hopefully there will be someone to take it. Alan Kennedy has the de-fib.
Regards to all.