Checking Main and Rotor Windings
* Stop the engine.
* Remove the two screws which secure the end cover to the
generator and remove the end cover.
* Disconnect the Automatic Voltage Regulator (AVR) (a).
* Remove the screw (b) that secures the brushes and remove the
brushes.
* Disconnect the yellow-, red-, black-, and green-marked wires
(f) from the terminal strip. On GP 2500A/GP 2600 models, disconnect the voltage
plug (g).
Using the Ohms setting on the multimeter, measure the
resistance of main winding 2 by measuring across the upper two terminals (c)
(yellow and red). On GP 2500A/GP 2600 models, measure across the red and white
wires. Also check the resistance of main winding 1 by measuring across the two
lower terminals (d) (black and green). On GP 2500A/GP 2600 models, measure
across the brown and blue wires. Each generator size will have a different
value. Check the chart in the graphic for the correct values; use a tolerance
of +0.5/-0.0 Ohm.
* If the correct resistance is not measured, the main windings
are bad; replace the stator.
* If the correct resistance is measured, continue.
Check each winding to ground. (Measure resistance between
the winding and the ground stud (x) of the stator. Measure both sides of the
winding.)
* If either winding has resistance to ground, it has failed.
* If both windings show no resistance to ground, they are OK
Using the Ohms setting on the multimeter, measure the
resistance of the rotor winding by measuring across the slip rings (e). Each generator size will have a different
value. Check the chart in the graphic for the correct values; use a tolerance
of +1.0/-0.0 Ohm.
* If the correct resistance is not measured, the rotor winding
is bad; replace the rotor.
* If the correct resistance is measured, the rotor winding is
OK.
Check for shorts to the rotor shaft by measuring resistance
between each slip ring and the end of the rotor shaft.
* If there is any resistance, the rotor winding has failed.
* If there is no resistance, the rotor winding is OK.
* If possible, the resistance of the insulation should also be
checked using a 500V megger or similar instrument. When using a megger, a
resistance value of at least 1 megohm should be obtained. Measure between each
winding group and the generator frame. If 1 megohm is not measured, dry out the
windings in a warm atmosphere and recheck every 30 minutes until 1 megohm is
obtained.
Checking Brushes
As long as the brushes have continuity and are long enough
to touch the slip rings, they should be functioning. To check the brushes,
carry out the following procedures:
Stop the engine.
* Remove the two screws that secure the end cover to the
generator and remove the end cover.
* Remove the screw (a) that secures the brush holder and
remove the brush holder/brushes.
Visually inspect the brushes (b) for cracks and for the
buildup of dirt. Clean the end of the
brushes if necessary.
* Check each brush for continuity.
* Replace the brush holder/brushes as needed.
