Power Tech Generators PTS-30 Operator's Manual page 166

plate carrying positive-biased diodes. Insure that correct polarity diodes are fitted to each respective
plate. The recommended torque for tightening diodes is 4.06 - 4.74 Nm (36-42 in lb).
The surge suppressor is a metal-oxide varistor (“"variable resistor”" used to protect circuits against
excessive voltage by acting as a spark gap) connected across the two rectifier plates to prevent transient
reverse voltages in the field winding from damaging the diodes. The varistor should read virtual infinity in
both directions with an ohmmeter. A defective unit will show visible signs of failure, and should be
replaced.
If the output is still low when separately excited, the main rotor, exciter stator and exciter rotor winding
resistances should be checked (see Resistance Charts), since the fault is in one of these windings. The
exciter stator resistance is measured across leads X and XX. The exciter rotor is connected to six studs,
which also carry the diode lead terminals. The main rotor winding is connected across the two rectifier
plates. The respective leads must be disconnected before taking the readings. Resistance values should
be within +/-10% of the values given in the tables below.
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