Your problem description invites a lot of Questions:
1/ Have you obtain, from the Parallax web site the trouble shooting procedures
for the 74NN converter series. If not, before throwing out your converter maybe try
the recommended tests.
2/ Do your various 12V lights, water pump, etc. work without shore power and/or the generator running. If they do not make sure the battery disconnect switch is in the connect mode. Note do not relay on the Battery switch light it will be on any time the
converter is operating.
3/ Iím not as familiar with FR vehicles as some on this forum but if you have a boost switch on the dash you most likely have what is called a Battery Control Center and in the BCC you will find the switches (actually there are solenoids) that sparks1032 referred to. A loose connection on a solenoid or a bad solenoid may explain why you do not see the 14Volts from the chassis charging system or a charging voltage from the converter.
4/ Also with in the BCC there is various fuses and circuit breakers you may want to check. In particular the reset-able circuit breakers.
The problem as you describe it lends itself to something that is common to both the chassis and coach charging systems, eg. The BCC, but assuming anything with out further information, would be taking the WAG approach to your problem