Champion 2000w inverter no power

I just purchased a pair of used inverters from a guy and he Told me the one doesn't output Power anymore. Eventually I will be using the parallel kit. I basically got that one for free and paid for the one that runs good. He doesn't know why it doesn't put power to the plug anymore, the engine still runs great. I am taking it apart to see, any ideas on what to test or look for? I was thinking the breaker switch might have tripped on him once and went for a crap. Any ideas please