a/c generator wont make any power ?

Hi ,first post, trying to fix my genny lent it out to a stonemason on site who ran it for a 9 "angle grinder cutting stone . I think it overloaded the genny and now it makes 6 volts ! what has gone ? any parts that are simple to replace .? a suggestion was that the coil may have burnt out ? can anyone help ,please?

Maybe a piece of stone is lodged in the throttle.

If the motor is operating properly and at full throttle, and you only get 6volts out, sounds like the regulator failed. The genset's circuit breakers should have tripped before it would have blown itself out from a grinder. You didn't mention the brand and model #. The inexpensive gensets use cheaply designed regulator circuits that often have capacitors and diodes failing. Good quality and industrial gensets will use slip-ring diodes and a rotating field to greatly reduce the number of electronic components needed for regulation. They generate clean power from the start, rather than generating a cruddy AC waveform that needs cleaned up via a bunch of electronics. Can you provide me with brand and model number? I assume the output is 6vAC and not DC? Some sets output both AC & DC.