There is a "120" volt fuse in most converters on the circuit board right where the 120v cord comes in.
If it quit from "overload" it might just need a reset. Tech support might help with that info when the manual doesn't.
If it is the in-rush thermistor that fried, it can be replaced. I changed mine out on the similar PowerMax 100 amper. You can tell if it that by fine cracks showing on the big disk and when you poke it pieces crumble off. PowerMax has since changed the circuit board and thermistor on their production models (mine is a prototype I got a few years ago now)
If you can't get the 68100 going, with your battery type and big bank you might be a good candidate for the PowerMax 120amp adjustable voltage model.
It would do that job and also give you voltage options for exactly meeting your battery specifications, including being able to fine tune that spec voltage for temperature ( a voltage vs temp table is available--Mark was it? posted one a while back here that I printed and find very handy.)
Found it. Half way down here
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/26669731/srt/pa/pging/1/page/1.cfm