It sounds like you have lost polarity on the Generator fields. You should have 2 or 3 vdc with the generator sitting, idling on inspection. I would check for correct polarity. If you do not have the DCV, I would look at the AC feeding your rectifier, I am assuming you have rectified DC and not an exciter, if in fact, you have an exciter, you may need to flash the circuit with DC from another source. Just guessing since I do not have a print. With a print, you should be able to easily track down your lack of DCV.