CYLINDER & SEAL GP-BOOM 3494126 - Caterpillar

diode range. Remove all leads from the rectifier block.
To test the negative rectifier block, follow these steps:
Place the red test lead on the negative "-" terminal. Place the black test lead on the following rectifier terminals: "AC1" (3) , "AC2" (4) and "AC3" (5) . All readings on the meter should be between 0.4 and 1.0.
Place the black test lead on the negative "-" terminal. Place the red test lead on the following rectifier terminals: "AC1" (3) , "AC2" (4) and "AC3" (5) . In all cases, the meter should read "OL" (overload).
To test the positive rectifier block, follow these steps:
Place the red test lead on the positive "+" rectifier terminal. Place the black test lead on the following rectifier terminals: "AC1" (3) , "AC2" (4) and "AC3" (5) . In all cases, the meter should read "OL" (overload).
Place the black test lead on the positive "+" rectifier terminal. Place the red test lead on the following rectifier terminals: "AC1" (3) , "AC2" (4) and "AC3" (5) . All readings on the meter should be between 0.4 and 1.0.Note: A shorted diode can cause damage to the exciter rotor. If a diode is shorted, check the exciter rotor. Refer to the Testing and Adjusting, "Winding - Test" and Testing and Adjusting, "Insulation - Test". Perform these tests.Note: For a failed rectifier block, refer to the "Diode Block Troubleshooting Guide", Table 3. The "Diode Block Troubleshooting Guide" consists of a list of items to consider when troubleshooting a failed diode block and/or external varistor (CR7). The purpose of this list is to find a cause for the diode block and/or varistor (CR7) failure which may be external to the exciter system. The purpose of this list is NOT to troubleshoot "no voltage output" from the generator.Note: This configuration contains an externally mounted varistor (CR7) block. Refer to Testing and Adjusting, "Varistor - Test" section of this document. Perform the tests in the "Diode Block Troubleshooting Guide".
Table 2
Diode Block Troubleshooting Guide    
   Check For    Measurement    OK/Failed    
Diode checks?     Diode short or open.            
    Internal varistor (CR7) OK or Failed.            
   
External varistor (CR7) check - OK or Failed?     A shorted external varistor can cause diode block failure due to overcurrent.            
    A failed diode block can cause the external varistor to fail due to the loss of the main rotor circuit, overheat, and then become an open circuit.            
   
Exciter end physical inspection?     General conditions            
    Loose or missing wires.            
    Heat transfer compound under diode block.            
   
Measurements?     Exciter rotor winding resistance and insulation resistance measurement            
    Main field rotor winding resistance and insulation resistance measurement.            
    Record ambient temperature when taking