They have a troubleshooting
CHART starting at page 25.
Without looking at the manual more I would try to excite it with a drill motor. Connect a regular electric drill motor into the power side with the generator running and hold the trigger and twist the drill motor by hand. Depending on the design some generators lose their residual magnetism and the drill motor will excite it enough to start output.
If that doesn't work I'd then do a visual inspection for loose or burned connectors and burned areas on circuit boards. Sometimes removing connectors and reinstalling will make a fresh contact and fix the problem.
Then I'd go to the chart and start pinning it out.
