Yamaha EF4500iSE Theory & Diagnostics Manual page 41

Use extreme care when handling the stator and
rotor . DO NOT set them on their windings .
Damage will occur .
Once the rotor has been removed, unsolder the
diode or diodes, depending on the model, using
caution not to damage it by overheating.
Set your meter to the diode checker scale or the
highest ohm scale if your meter does not have a
diode checker. Test across the diode and note the
reading.
Switch the meter leads and test again, noting the
reading. You should have continuity, or a resistance
reading, in one direction, but not in the other direc-
tion.
The diode is bad if you have continuity in both direc-
tions, or an open circuit in both directions.
The last step is testing the Main Field Coil or better
known as the rotor windings.
The resistance test must be done with the diode(s)
still unsoldered. Connect the meter to both ends of
the rotor windings, using care not to touch both
leads with your hands, as this will cause the meter
to read your body's resistance.
CHECKING ROTOR RECTIFIER
IN ONE DIRECTION
CHECKING ROTOR RECTIFIER
IN OPPOSITE DIRECTION
ROTOR RESISTANCE TEST
2-7
Generator Diagnostics