I worked on a friend's generator at his camp in the swamp. Same symptoms as yours. I disconnected the negative battery lead (safety first!). I removed the controler board cover, found a mouse nest. Cleaned out the nest and looked at the board. The board was sealed, in a resin like substance, but I could see burned resistors. Of course being seald we couldn't do anything about it. Had to get a new board. I recall it was in the price area of $225. Installed new board and off and running. You may or may not be able to see damaged components. Resistors usually burn, capacitors burn or the electrlytic (look like little cans) bow up at the top or blow the can right of. Other chips may have small pieces blown off by the leads going to the board. if you see any of them, you should probably replace the board or find a GOOD electronics technician. Good luck.
2013 Cardinal 3800FL
2009 GMC 3500HD CC LB SRW