Peculiar alternator problem

[2seater]

I just had an experience which may be of some use to anyone with an elusive charging problem. The electrical problem light came on and when I checked the alternator with a voltmeter, there was nothing happening. I checked the diagnostics and there was code B431, charging system problem. When I went through the diagnostic tree, it confirmed the alternator was bad. I took the alternator back to the place I purchased it, ready for a fight. There is less than 5000 miles on it and they agreed it still looked brand new. They put it on their machine and it would work, but only at certain rpms. When they tore it down, they found a broken wire in the rotor (maybe the stator), which he said he had only seen twice before in 23 years. The happy ending is they replaced it for free even though it was long out of warranty, plus I don't have the receipt. He showed me the output of the new one before he gave it to me, 126A. @ 13 volts.