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.