roy.c,
Welcome to the forums.
Most of the control systems on an RV run on 12 volts. If the converter doesn't work then the batteries supply the needed power until the voltage gets extremely low. Then none of the devices work.
I'd add a battery charger--for testing purposes.
It is possible that the fuses on the converter have blown. There are often 2 and sometimes 3 right on the converter itself.
Once you have 12 volt power restored you can begin checking the other devices.
One device that doesn't use 12 volts at all is the microwave--so see if that works.