" That wasn't 42 VAC out of the converter! That was 42 VAC at the cable end going into the converter."
Not understood. The 120v to the 7300 is not from a "cable" The converter input is a black wire and a white wire. the black goes to the bottom of a 120v circuit breaker above that on the AC panel, while the white wire goes over to the neutral buss with the other branch neutrals.
Where exactly did you have the two meter probes when seeing that 42 volts? Also does anything else 120v work, like the microwave, things plugged into the 120v receptacles?