Either work your way forward, check 120 power to the converter, (it's on a breaker), then if that is there check the output terminals of the converter, then if that is good, check at the battery to see what the voltage is there; or work your way backwards, check at the battery to see the voltage there, then the converter terminals, and then the input.
Recently my converter was producing full power, but the wires connected to the output to the battery were loose resulting in a hot white wire (that's how I found it), so check that first!
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel