Thanks for the suggestions guys.
I'll whip the bridge off and check the ground cable.
By the ground do you mean the earthing cable??? If so, my understanding was that all this did was to help eliminate a general electrical hum, but as I said I'm no expert and will believe almost anything I'm told!!!
The circuit is not epoxy coated but it is covered with a sticky backed peice of high density foam (ala blue Peter). I'm reluctant to try and peel this off in case it does more damage than good..... What componants I can make out though are very tiny indeed so as you say trouble shooting could be a real ball ache.
To be sure it is the preamp that's at fault, is it possible to rewire the bass to bypass the cicuit and run it as a passive instrument?
Could it equally be a duff pickup that's behind the problem?
I have been half heartedly toying with the idea of whipping the guts out of the bass and converting it to a passive model anyway (maybe lob in a pair of SD quater pounder jazz pups) but I'd like to know what the faulty componant is to be able to sell the 'working' parts with a clear conscience!! Don't get me wrong, the Bartolini pups and eq are amazing, very clean, clear and defined - it's just that I prefer the warmth and tone of passive pups so this fault could perhaps force the issue.
My thoughts aside, anyone else have any wisdom to shed on this problem please?