Duke37, Is that an old Field Marshal Tractor? I have attached a 12v battery to the brushes (per instructions), and used a 9v battery to the receptacles per the Generac web site. Are you suggesting using the 110v house supply connected to the generator with lights method. I have worked with 550 3 phase, and many other voltages, but I must admit the thought of connecting 110v directly to a portable generator scares me. 30 years ago I had lots of test equipment and access to many others but now I have only my old Simpson 260 and a few digital meters.
Dorke, I pulled the brushes, looked great, tested good with my ohmmeter, did the same to the windings. I must admit though I can only test them through generic readings as there is no data on this unit that I can find anywhere. It was sold by Dayton (out of the generator business, and no archives), and manufactured by Generac (again no archives at Generac, but they are more than willing to sell you a new one as this one is not worth repairing). Also, the diodes you asked about, the one that goes left to right on the image is a BZY97C130, the one that goes up and down starts with BZY and can't see the rest yet but I suspect it is the same type. A web search of those showed them as Zener diodes and of course too high a voltage to see if my $7.00 Zener diode tester actually works.
As to the diodes that started this thread, removed the potting around the first one, then removed the diode using a soldering iron and solder sucker. Began to remove the potting around the second and the diode pulled apart where the anode connects to the wire. My fault, probably, but I was using a razor to cut the potting away and not prying on it. Also found the wire that connects to the excitation had maybe one strand and the potting holding it to the board.
These are merely bumps in the road though, if this generator is fixable I will fix it. Then of course sell it for a loss or give it away and get some other project.