Generator Output Voltage

[crissrace]

We were dry camping at the Formula I race at Indianopolis Speedway last
weekend when both the air conditioners quit. Quick investigation
revealed that the generator was running but no output. I checked the
breakers and the voltage to them was 84 volts on each leg. 120 would
have been better. There are 1400 hours on the unit. Does anyone have
an idea where to start to repair this fault?
Any and all help appreciated.
Bob Criss
1990 SP36
143000 miles