Back again. After a long and involved testing routine with loads of red herrings I believe I have identified the problem. It is the Alton. The Podtronics was sent to Al Osborn of Norton fame for testing and passed as perfect. This left me back to square one. I retested the Alton using Al's advice, with the bulb. I got a bright bulb between the output wires, but I also got a glow between a wire and earth. This shouldn't happen, it implies the Alton is earthing somewhere. Tests off the bike showed continuity between the wires and straight to earth also, so the stator (virtually new) is dead. Stripping the unit shows evidence of contact on the rotor and one of the support bearings is loose in the case, the other is tight is the case, but evidence of looseness. My conclusion is the whole thing is duff; the rotor is still magnetic, but I wonder if the contact was what unscrewed the central screw? The Case itself may be worn, so there's no point in fitting new bearings. I believe it's possible that all the damage is due to the rotor wobbling in the bearings (clearance between rotor and stator is quite tight. Seeing as the oldest this version of Alton can be is 2009 and the bike hasn't done a huge mileage, does it make sense to fit another (£445 + postage) or pursue a cheaper option? Photos of the innards of the Alton enclosed.