Diesel Generator voltage/ frequency failure 6

[mortimouse]

Any advice greatly appreciated.
Machine type cummins/onan admiral 400v genset. Started the machine today and only producing 200 v/phase as oposed to 400. Also no frequency registered. Have manually adjusted engine speed however there is no change. I am reasonably certain that the governing system is operating as it should.
Can anyone tell me what the likely cause is.
Many thanks in advance.

 

[mortimouse]

one last thing. It is possible to remove said pot by jumping terminals 1 and 2 on the AVR. Have done this to both machines and will leave them at that. It is such a hassle to remove the sound proof casing to access any of it that in my opinion the secondary pot is surplus and nead not be considered. Again all those who helped, thank you.