something occurs to me, that you can easily check
the little white plastic junction strip mounted on the lower part of the transformer unit, it is not original equipment.
what i don't know is this...
does the output wires going to the load connect through this strip normally?
i think the load wires are connected to the strip? it looks that way in the schematic.
what concerns me is this, that type of junction strip or at least some of this type aren't really capable of transferring the amount of power the generator is capable of through the strip bus.
you might take a look and see, check each to see of there is continuity across them, and that there is no signs of overheating there.
its a reach, and i can't tell from the pictures, but if as it is my experience the terminal strip cross connector(s) might be blown out like a fuse having failed.. and we would assume the connections to be good when maybe they aren't?
doesn't take much to check out and see.
again we know that the basics of the generator are good, i went back and reread the manual and the diagnostic flowchart "again" (funny how one learns a bit more with each reading). on page 11 left column, second group
where it says voltages correct and equal, and from above (center) the voltage should be approx 170vac and you got 169...
the flowchart then says it is a problem with the transformer (OREX), to inspect and change if necessary.
so everything is telling me it is a faulty transformer, however it may be the terminal strip with bad conductors, or someone has misconnected things?
we are cornering this gremlin! he ain't gonna get away from us!
bob g