I lost all my 12v systems the first trip out in my 3850RL in 2012. In my unit, the converter/inverter box is located behind the basement main storage compartment left side bulkhead (wall) when you face the storage compartment on the entry door side. Not surprisingly, the converter unit was pain to get to as I had to remove quite a number of retaining screws to peel the wall out enough to gain access. The good news was the converter/inverter electrical system and cables were reachable while bending into the compartment from the outside of the trailer. There was a large fuse on the converter/inverter and mine was fine. I ended up just having the unit replaced under warranty. Another hint: In my unit, the circuit breaker and fuse panels are located low and to the right of the entry door foyer area. The inverter/converter unit was mounted behind those panels but again accessed from the storage area. Lastly, check the type of screwdriver you will need to remove the wall. My unit had the "square head" screws and I now keep that screwdriver on the rig. Hope this helps.
Mark & Susan
2012 Infinity 3850
2014 Ford F350 6.7 Super Duty King Ranch, CC, Long Bed, SRW, w/ Q20 Curt 5th Wheel hitch