PUMP-PNEUMATIC 1915347 - Caterpillar

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Selection of the Crowbar Test in Cat ET
In the main screen for the Motor 1 ECM, select “Diagnostics” from the menu bar. From the pull down menu, select “Diagnostic Tests”, then select “Overvoltage Control Rectifier Test” (Crowbar Test).
Follow the instructions that are presented on the screen in order to satisfy the preconditions for the test. As the conditions are satisfied, the condition will be “grayed out”. The ECM will not allow the test to proceed until all preconditions are satisfied.
Once the preconditions and the setup conditions are satisfied, the user will be given the option of turning ON the ECM driver circuit for the Crowbar or turning OFF the ECM driver circuit for the Crowbar.
When the instruction states: “To turn ON the overvoltage control rectifier, click the Next> button”, clicking the NEXT button on the bottom left-hand side of the screen will activate (close) the crowbar thyristor. When the instruction states: “To turn OFF the overvoltage control rectifier, click the NEXT button”, clicking the NEXT button on the bottom left-hand side of the screen will deactivate (open) the crowbar thyristor. Note: When the Crowbar is commanded to close, the Cat ET screen will not provide an indication that the Crowbar is activated or closed. This operation will be checked in the following steps. After the test is completed, the “Successfully Completed” message only indicates that the test is done. The message does not indicate that the circuits or the Crowbar have operated properly.
At the bus bars in the front of the Crowbar compartment, use a multimeter to check the resistance across the thyristor. Place the positive probe on the positive (+) bus bar. Place the negative probe on the negative (-) bus bar.
Observe the resistance measurement. The resistance should be high or infinite (OL).
Close the Crowbar thyristor. The resistance should change to a lower resistance value.
Open the Crowbar thyristor. The resistance should change to a high or infinite (OL) resistance value.
Reverse the multimeter probes. Place the positive probe on the negative (-) bus bar. Place the negative probe on the positive (+) bus bar.
With the Crowbar thyristor open, observe the resistance measurement. The resistance should be high or infinite (OL) resistance value.
Close the Crowbar thyristor. The resistance should remain at a high or infinite (OL) resistance value. Expected Result:The resistance measurements are indicating that the operation of the Crowbar thyristor is correct.Results:OK - The operation of the Crowbar thyristor and the control circuits is correct.The test is completed. The Crowbar is operating properly.STOP.NOT OK - The resistance measurements did not register as expected when the thyristor is cycled ON and OFF. There is a problem in the control circuit or with the crowbar assembly.Proceed to the next “Troubleshooting the Crowbar Circuits” section in order to check the operation of the control circuits.Troubleshooting the Crowbar Circuits
The following troubleshooting steps will help to determine if there is a problem in the control circuits or a problem with the thyristor.
Illustration 4 g02135033
Crowbar Thyristor that is located in the lower left hand