Jim I just got off the phone with Mr. G he said to shut the good inverter down, give a hard rap with your knuckles on the front of the faulty inverter in the upper right hand corner and see if the charger starts.
He has seen many loose connections to the internal switch that would cause this and that is where it is.
He also said yours are still not obsolete parts are still available for them out there and many repair shops are in the habit of just replacing the board to the tune of 600 bucks and they are repairable for much less.