Hello everyone. I encountered an issue where a machine was running smoothly until the power was turned off for the weekend by the client. Upon restarting the machine on Monday, it's no longer functioning properly. I have checked the hardware and program, and the BATT LED is on, indicating no issues. I also found some Overridden values which I cleared. The PLC RUN LED responds to the run and stop controls, and the status shows Run Enabled, but the program is not being executed. As I am not experienced with PLCs, I am unsure if there are any other troubleshooting steps I can take before considering replacing the CPU. Your suggestions would be greatly appreciated. Thank you. - Diogo CD
If the BATT LED is illuminated, it signifies that the battery is unable to retain RAM during a power outage. Your CPU may be set up to recover from the program stored in flash memory when it restarts with the RAM memory wiped. Consequently, the initial values of certain variables might differ from what was used previously. Additionally, there could be discrepancies between the saved version in flash memory and the actual running program. The screenshot you posted could result from the variable being written to a different location in the program or being part of a subroutine that was not activated during the screenshot capture.
In the past, I have encountered problems with the 90-30 system where outputs would become disabled during powerdown or powerup events. Although I cannot pinpoint the exact location in the menus, look for an option in the top menu bar related to activating outputs. This issue is commonly searched by users of the 90-30 system as they try to troubleshoot problems with output functionality.
When the BATT LED on a programmable logic controller (PLC) is illuminated, it indicates that the battery is unable to maintain RAM during a power outage. In this situation, the CPU may be set up to reboot using the program stored in flash memory, resulting in the RAM memory being cleared. Consequently, there is a possibility that the initial values of certain variables differ from those used previously. It is also possible that the data saved in flash memory may not perfectly match the previous operational state. The displayed screenshot may result from variables being written elsewhere in the program or from a subroutine that was not activated during the screenshot. Despite checking for any hardware or program loss, the issue persists. This discrepancy serves as an example of the PLC malfunctioning, as the variable is exclusively written in a specific block that is indeed being accessed. Additionally, the timers are not functioning, suggesting that the CPU is not executing the program properly, even though the RUN LED is illuminated.
In previous experiences, users have encountered problems with the 90-30 system where outputs would become disabled during power cycles. While it may vary in location within the menus, look for an option in the top menu bar related to re-enabling outputs. When connected online, it should display "RUN Enabled" status.
I have never faced this type of failure before, but we cannot dismiss the possibility of a faulty CPU. Have you checked the CPU fault table for any entries? Are all coil instructions affected, including both %M and %Q addresses? When researching other uses of the %M address linked to the malfunctioning coils, did you conduct a thorough search? This could reveal hidden usages within MOVE instructions that include the specific address you are seeking. Have you attempted toggling the %M or %Q bits on and off? If you can change a bit's state regardless of the logic preceding the coil instruction, it suggests the program is not running properly. If you cannot alter its state, something may be keeping it in its current state. Try the same approach with the malfunctioning timer. Changing the %R address for the timer instruction can indicate if the program is not assessing the rung with the timer instruction correctly. Verify the hardware configuration to ensure it is set to retrieve program and register memory from flash. If it is not, you may have reverted to an older setup that was controlling the machine before.
Hi Diogo, it sounds to me like you're dealing with a potentially tricky situation. Since you've already checked the hardware and software, I'd suggest looking into the possibility of a power surge when the machine was restarted. Such a surge may have corrupted the CPU or memory; hence, the program isn't executing even with "Run" enabled. Try performing a complete memory reset or re-uploading the PLC program, if you have a backup. If this doesn't work, then a CPU replacement might be the next step.
Hey Diogo, happy to offer some advice. Given the circumstances, it's possible that the issue could be with the PLC input/output modules rather than the CPU itself. I would suggest taking a close look at the input/output status indicators if your PLC has them present. Also, don't forget to cross-verify with the actual input/output wiring status. Additionally, try to check your code as well. There might be an issue with a start-up sequence in the code since the problem started after a power-off. Do keep us updated!
Hey Diogo, it sounds like you've done a good job troubleshooting so far. One thing to consider might be checking the integrity of your PLC program. If a program has been corrupted it may seem like everything is operational, but the execution could fail. If possible, try reloading a backup of the PLC program into the CPU and see if that resolves the issue. If you do not have a backup, reviewing the code for any inconsistencies could be beneficial. Lastly, a factory reset might be necessary as a last resort, but keep in mind this should be done very cautiously as it will wipe out everything and you'd need to reinstall the program from scratch. If you're uncomfortable proceeding any further, don't hesitate to loop in a professional to help you take these next steps.
Hi Diogo, sorry to hear about your machine problems. Since you've already checked the hardware, cleared overridden values, and the BATT and PLC RUN LEDs indicate no issues, you might want to consider checking the communication wiring and related components. Sometimes, a brief power surge during a restart might affect these. Also, make sure you're not skipping any PLC boot-up sequences with the power cut. Try testing with a simpler program to check if the CPU is executing that at all. If it isn’t, you might want to consider a software or firmware issue. However, if you're unsure and not too experienced, it might be best to get a professional engineer to diagnose the issues.
Hi Diogo, it sounds frustrating to deal with such an issue! Since you've already checked the hardware and cleared the overridden values, you might want to confirm if there's any fault code being indicated on the PLC. Sometimes, a reset can help if something's stuck in a fault state, so try cycling the power again after a complete shutdown. Additionally, double-check the I/O configurations and any connection issues that could have arisen during the power off. It might also help to look at the event logs if your PLC has that feature, as they can provide insights into what happened during the shutdown. Good luck, and I hope you can get it running smoothly again!
Hi Diogo, it sounds like a frustrating situation! Since you've already checked the hardware and cleared the overridden values, I’d suggest checking for any fault codes or error logs in the PLC's interface, as they might provide more insight into what’s going wrong. Also, make sure all the connections are secure, particularly after the power loss—it’s possible something got slightly loosened. If you haven't already, try a complete power cycle (turn it off, wait for a minute, then turn it back on) to see if that helps reset any internal states. If all else fails and the PLC is still unresponsive, consulting the manufacturer’s support or forums specific to your model could uncover common fixes. Good luck!
Hey Diogo, it sounds like you’ve already done a solid job troubleshooting! Since the PLC is showing that it’s enabled but not executing the program, I’d suggest checking if there might be any safety interlocks or fault conditions that could prevent execution. Also, try rebooting the PLC to see if that refreshes the system—sometimes, a simple reset can help resolve these weird issues. If all else fails, consulting the manual for any diagnostic modes or looking for error codes might provide more insight before considering a CPU replacement. Good luck!
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Answer: Possible reasons could include overridden values, program errors, communication issues, or hardware malfunctions related to the CPU.
Answer: You can start by checking for any overridden values, verifying the program logic, ensuring proper communication setup, and inspecting the hardware components for any faults.
Answer: The BATT LED being on indicates that there are no issues with the battery backup system, which helps retain memory and settings during power loss.
Answer: You can typically clear overridden values through the programming software by identifying and resetting any manual overrides that may be affecting the program execution.
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