A friend has a ?40-50 kVA, 240 V, single phase generator, of 1970s vintage, coupled directly to an engine. It was working fine but now produces no power at all. All the brushes and spring holders are fine, as are the fuses. I can't find a decent description/diagram of the internals, other than very basic animations of the principles of AC generation. Does anyone have any tips on what to check, or where to look for information? Within the generator body is a large capacitor, a 40A bridge rectifier (which is good) and four heavy-wound coils (?tranformers). It's hard to see what goes where as the wires are hard to get to and covered in dust. Also, there's a button marked 'excite' which seems to make no difference, although I've metered it and it works as a SPST switch shorting two wires together. What are all these bits for? I did clean the excite switch once and got the generator working again, but only briefly, and I suspect it was just a coincidence.