Are you sure it is an inverter type generator? Could be direct AC generation instead of inverter.
I couldn't find a model 593 either. Gas or diesel or LP? Size?
In any case, you are talking big bucks to fix this. Either the inverter or the half wave alternator that feeds it is an expensive part. And if it is not inverter power, then the AC generation parts are equally expensive. I gather it is not installed in anything right now, so that saves a lot of labor, but I'll still bet we are talking upwards of $1000 and maybe $2k. They ought to give the the generator so you can afford to fix it.