DISC ASSEM. 4S8695 - Caterpillar

Troubleshooting
General
Before working inside the generator, make sure that the starter motor can not be activated by any automatic or manual signal.
When the engine-generator is operating, voltages up to 600V are present in these areas near or on the regulator: 1. the regulator terminal strip2. the excitation transformer terminal strip (self-excited generator only)Do not short these terminals to ground with any part of the body or any conductive material. Loss of life or injury could result from electrical shock or injury from molten metal.
An electrical shock can be received from the regulator capacitor (C1) when the engine-generator is not in operation. To avoid possible injury, discharge the stored charge using an 100 ohm resistor across C1 terminals.
Electronic components in the regulator can be damaged during generator operation if contact is made between the part and ground.
The following general rules should be read and used as a guide when troubleshooting a generator:1. A large percent of the electrical problems are caused by mechanical defects. Take time to carefully inspect the total installation. Keep the mechanical defects separate from the electrical defects.2. The generator is basically a constant speed unit. RPM that is 5 to 10 percent higher or lower than the rated rpm can cause terminal voltages that are 5 to 10 percent higher or lower than the rated output.3. Generator heat is caused by line current. The higher the line current, the hotter the generator will become.4. A voltmeter and ammeter or kW meter does not necessarily show the KVA load on a generator because of the power factor of the load.5. Before working on the generator, the operating principles must be understood.6. Find the operating trouble and use the wiring diagram and troubleshooting guide to find the probable cause.7. When troubleshooting for voltage, a generator can normally be operated at a low rpm. Voltage and frequency will change directly with rpm.8. Where the same adjustments are necessary on two or more units, (as in parallel operation) use the same instrument for measuring all voltages.Test Instruments
Caterpillar Digital Multimeter - can be used for many of the voltage and resistance checks. Rectifiers can also be checked with the special diode function. For further information on using the digital multimeter, see Special Instruction, Form SEHS-7734-01. Caterpillar AC current probe (clamp-on type) - used with the Caterpillar Digital Multimeter, it can measure current in the range 10A to 1000A rms (at a circuit-to-ground voltage of 650 rms maximum). See Special Instruction, Form SEHS8011 for warnings and information on how to use the current probe. Volt-ohm-milliameter (needle movement type) - In many of the following resistance test procedures, the ohmmeter connecting polarity (positive or negative) is given for testing the respective component. The identification of lead polarity on ohmmeter instruments is not necessarily the same.
POLARITY CHECK OF OHMMETER TERMINAL
1. Selector switch. 2. Selector switch. 3. Mark to show polarity of ohmmeter cables.Volt-ohm-milliameter cable polarity must be known. The red, positive "+", color on the cable of an ohmmeter can be either positive (+)