Questions about the S7-300, please help

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This post was last edited by warewood on 2020-3-24 at 15:26. We have a system here that uses a Siemens S7-300 PLC. There are four expansion cabinets below, with a total of 30 modules. The PC side uses a WIN7-32-bit system with WINCC version 7.0. A situation has arisen now: suddenly the screen display shows an exclamation mark, no operations are possible, STEP7 is not available online, but the network PING works fine. Only by restarting the CPU can it function properly. It’s happened like this for a week now; it can last a few hours in some cases and several days in others. It still happens even after the CPU and communication module have been replaced. Also, during normal operation, an exclamation mark will appear on a certain screen to indicate data issues, but it returns to normal after a few seconds. Due to design reasons, there are several frequency converters within 2 meters of the site. 100 days have passed since the last lower-body procedure. During that period, the SF red light on the CPU was on as well; when the system was working normally, diagnostic programs indicated that there was a fault with the CPU yet it still functioned properly. This issue persisted even after replacing the CPU. I hope some experts can analyze the source of the fault. Thank you!