Yamaha EF4500iSE Theory & Diagnostics Manual page 37

Generator Diagnostics
TROUBLESHOOTING PROCEDURES
FOR NON-AVR TYPE GENERATORS
Occasionally, the rotor may lose it's residual magne-
tism and make it impossible for the generator to
begin the cycle of electricity. This can be caused by
prolonged periods of non-use or from the shock of
being dropped. If the problem description was
something like, "The unit has been unused for quite
sometime and it worked fine the last time it was
used, but now has no output" or "The unit was work-
ing fine until it was dropped while being loaded onto
the truck, and now it has no output. This could be
the cause.
This repair is actually quite simple. First verify the
problem by starting the engine, then turn the AC
protector to the "ON" position.
With your meter set to a high enough AC scale to
accept 200 volts, insert the meter leads into the
receptacle, polarity is not important.
If there is little or no output, remove the generator
end cap and locate the sub-coils 2 pin connector
with the two green wires.
NOTE: The sub-coil wires on most conventional
models are green but check the manual of the
model you are working on for exact colors and con-
nectors.
With the generator running, apply a 12 volt DC
REMAGNETIZING ROTOR
power source to the two green wires, again, polarity
is not important, for about 5 seconds.
Recheck for output at the receptacle. If power is now
G
restored, turn the generator off for a minute or two.
G
Restart the generator and again check for voltage
output.
If voltage is restored, you should still make any
minor adjustments such as frequency, which is
directly related to engine RPM and is adjusted with
the governor, as well as check the operation of the
generator by using a generator test set.
If the voltage was not restored or the unit came in for
another problem such as low voltage, further trou-
bleshooting will be required.
Because voltage output is directly related to engine
speed, a low voltage problem may be caused by
incorrect engine RPM. So, check that first.
Using a tachometer, set the engine RPM to the RPM
specified in the Service Manual. In most cases it will
be 3,750 RPM, without a load. Then recheck the
voltage at the receptacle. If the voltage is correct,
the problem is fixed.
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