Yamaha EF4500iSE Theory & Diagnostics Manual page 46

Yamaha Generator Theory & Diagnostics Guide
And last, check for the Sub and Main Coils for being
shorted together.
If the problem was not found in any of these areas,
proceed to the condenser test using the analog
meter.
Check to see if the needle swings and then returns,
replace it if it does not.
Some models are equipped with a voltage adjuster
that should be tested per the Service Manual's
specifications.
It is a variable resistor that should show a smooth
rise in resistance as the knob is turned from one end
of it's scale to the other.
If the voltage adjuster shows an open circuit through-
out the scale or at any one point in the scale, it
should be replaced.
It should also be replaced if the resistance is out of
specification.
Next, remove the rotor assembly to test the rotor
rectifiers, the exciter armature coil and the main field
coil.
Unsolder the coils from the rotor rectifiers, noting
where the wires go for reference when it comes time
to reattach them, and test the diodes in the same
manner as on the non-AVR model. There should be
continuity in one direction but not the other.
MAIN AND SUB-COIL
SHORT TOGETHER TEST
CONDENSER TEST
ROTOR RECTIFIER TEST
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