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Old January 31st, 2006, 09:38 PM   #1

garret is offline
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cpu fault on allen bradley slc500

can you tell me how to clear a cpu fault,and what would have caused it
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Old January 31st, 2006, 10:05 PM   #2
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bernie_carlton is offline
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The fault light, if solid, generally indicates a hardware failure. If blinking usually indicates a problem with the application. To get any more specific requires numbers only obtainable by hooking up the programming software and reading the specific fault. Then more detailed advice can be given. Your question is a little like 'my car stopped, what's wrong?'
Controlling outputs is the PLC's way of getting its inputs to change.
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Old January 31st, 2006, 10:14 PM   #3
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dalem is offline
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Cycling the power (rebooting) the PLC might handle it. Depends on what the fault is and what caused it. I had one fixed PLC that did this periodically. Always had to re-download the program to it. Then I added an EEPROM and programmed it to load from the EEPROM at each cycling of the power. (Only cycled the power when the CPU faulted out. The problem progressively got worse though. Come to find out, a capacitor or 2 on the powersupply (built into the fixed processor) had become desoldered from the circuit card, which must have been causing surges.

Another thing I recently did, was to do some math instructions, which caused math over flows, which caused the CPU faults. This was in a project, I was working on, off to the side, and basically, I did it on purpose.

Some CPU faults can only be reset if you have the SLC500 programming software. If such is the case and the program is not lost in the PLC, should be able to go online and see what caused the error. This would be found in the processor status, under the errors tab. With out the programming software and/or a backup copy of the application, you might be in trouble.
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Old February 1st, 2006, 12:04 AM   #4
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TConnolly is offline
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If you have a SLC 5/03, 5/04 or 5/05 you can change the keyswitch to program, then back to run. This will clear a fault and resume the program. If you have RSLogix 500 or know someone who does I recommend connecting to the PLC and finding out why it faulted by checking the fault code.
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