Thanks for the replies, I'll have to dig out the multimeter and figure out where to begin. U7 sounds like a good shout. I think I'll remove U8 as well just so I can remove any gunk from underneath it - U7 had quite a bit. It's annoying that I can't immediately see any rotten bias - that would make my job considerably easier. Any tips or links to using a multimeter for this task? Cheers.