I have a 15 year old Amana furnace GUCA070BX30 with a PCBBF118S circuit board. The humidifier has stopped working. The 24 volt transformer is not getting any 110 from the circuit board with the furnace and fan running. Does this mean that the circuit board is bad or could there be some other problem?

Normally, the humidifier terminals are energized with the burners.

You could try the terminals for the electronic air cleaner. They will be energized during a blower call.

Wouldn't that activate the humidifier during air conditioning also?

Yes, but for testing purposes, it would verify operation.

If there's no power on the humidifier terminals, you could wire the low voltage side to the thermostat connections (C and W).