Just another point to be considered: The need to "flash" the unit.
Sometimes, when a generator has been in inactivity, the residual magnetism in the rotor is too weak to generate enough voltage in the stator windings to initiate a closed loop and reach the operating levels of magnetism necessary to maintain the nominal output voltage level.
In this case, exactly, the reported problem is a low output voltage (55 VAC). This voltage, in absence of an excitation current is due purely to the magnetic remanent field, which in normal conditions, would feed the exciter field, increasing the voltage generated, increasing the exciter field and so on.
This is a brushless generator. Instead to feed the rotor windings using brushes and slip rings, in the rotor shaft there is an extra rotor. This is an alternator rotor in which an AC voltage is generated and then rectified by a set of diodes, included in the rotating mass. They are known as the rotating diodes and are connected directly to the main rotor windings to induce electric power in the main stator. This auxiliary rotor receives a magnetic flux from an auxiliary stator named exciter coil, fed by the AVR.