Ok. guy called Andy Viccars has been over it, re soldered the joints and put a new tab on the bridge earth.
Still no joy. Tried today at home. Yamaha TRB was totally silent. Plugged the Rick back in and the buzz was there. Have included a link to a little video i took of the problem. If people could have a look and help it'd be hugely appreciated.
https://www.youtube.com/watch?v=cAJfqIG0CN0