88334A 4 Mercury MERCATHODE ASSEMBLY

Illustration 1 g00643710
System Schematic For AC Transformer Box (ATB)
When the engine-generator, or any source to which the engine-generator is synchronized to, is operating, voltages up to 600V are present in the control panel.Do not short these terminal with line voltage 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.
The display of the GSC is showing 0 volts or 0 amperes for one or more AC phases with the genset that is running and the load that is connected.For AC voltage problems, begin troubleshooting at step 1.For AC current problems, begin troubleshooting at step 4.
Check the fuses.
Check the three fuses on the AC transformer box (ATB). The fuses should not be blown.Expected Result: The fuses should not be blown.Results:
OK - Fuses are OK. Proceed to next step.
NOT OK - One or more of the fuses are blown. Check for a shorted component or wiring error. Troubleshoot the fault and repair the fault. See the "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics and Wiring Diagram". STOP.
Check the generator output.
With the engine running and the circuit breaker open or the load removed, measure the voltage between all three fuses on the ATB. Expected Result: The line to line voltage should measure correctly for all three phases.Results:
OK - The voltages are correct and the problem remains. Proceed to next step.
NOT OK - One or more of the voltages are NOT correct, the wiring or connections are faulty. Check for wiring errors between the ATB and the generator buss, see the "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics And Wiring Diagram". Also check the electrical connections at the ATB terminal. See Testing And Adjusting, "Electrical Connector Inspection". STOP.
Check the connections.
Stop the engine.
Check the harness connector and crimp terminals of the ATB.
Check the GSC harness connector. See Testing And Adjusting, "Electrical Connector - Inspect".
Check for one or more broken wires between the ATB and the GSC. See "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics And Wiring Diagrams". Expected Result: All connectors are OK and the problem is no longer present.Results:
OK - All connectors are OK and the problem is no longer present. This procedure has fixed the fault. STOP.
NOT OK - Problem remains and concerns AC voltage. It is unlikely that the GSC is faulty. Replace the ATB. If the problem persists, then replace the GSC. STOP.
NOT OK - Problem remains and concerns AC current. Proceed to next step.
Check the current transformers.
Stop the engine.
At terminals 51, 52 and 53 of the ATB, disconnect only the wires that lead away from the ATB. These disconnected wires go to the current transformers (CT1, CT2, and CT3).
Measure the resistance from terminal 50 to each of the disconnected wires. Expected Result: The resistance should be less than 5 ohms.Results:
OK - The resistance is correct. Therefore, the current transformers are good. Proceed to next step.
NOT OK - One or more of the resistance measurements are NOT correct. A current transformer or related wire is open. Check for an open CT or wiring. See "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics And Wiring Diagrams". STOP.
Check the ATB.
Stop the engine.
Remove the harness connector from the GSC.
At the GSC harness connector, measure the resistance: from contact 4 to contact 16, from contact 5 to contact 16 and from contact 6 to contact 16. Allow each measurement to stabilize. Expected Result: Each of the three resistances should be 120 20 ohms.Results:
OK - Proceed to next step.
NOT OK - One or more of the resistance measurements at the GSC harness connector is NOT correct. Therefore, the ATB or the related wiring is faulty. Check for an open or short in the wiring from the GSC harness connector to the ATB harness connector. See "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics And Wiring Diagram". Check the electrical connections at the GSC and ATB harness connectors and at the ATB terminal strip. See Testing And Adjusting, "Electrical Connector - Inspect". If necessary, repair the wiring or replace the wiring. If the fault is not found, replace the GSC. STOP.
Check the ATB. The wires that were disconnected in step 4 remain disconnected. The only wires that are connected to these terminals should lead into the ATB.
At the terminal strip of the ATB, measure the resistance: from terminal 51 to 50, from terminal 52 to 50 and from terminal 53 to 50 . Expected Result: All resistances should be less than 1 ohm.Results:
OK - All resistances are correct, then the ATB checks good. The fault is in the GSC or the GSC harness connector. Check the GSC harness connector. See "Generator Set Wiring Diagram" in Testing And Adjusting, "Schematics and Wiring Diagram". If the connector is good and the fault remains, then replace the GSC. See Testing And Adjusting, "EMCP Electronic Control (Generator Set) - Replace". STOP.
NOT OK - One or more of the resistance measurements are NOT correct. The ATB is faulty. Replace the ATB. STOP.