I have a 28V 20A B&C standby alternator system which is only putting out 20 volts at 1200rpm. B&C took the troubleshooting report of ohms and volts from various components which I sent them, and say it's the alternator. (its got 800hrs on it) Adjusting the voltage regulator up does nothing. They say the field voltage is normal. Just wondering what failure modes could cause this. One brush failed? A diode? Thanks for any ideas.