Simatic S5-155U BASPA Low Voltage Signal

Hi everyone,

I am encountering some problems with a Simatic S5 system comprised by CPU 946/947, CP525, CP 527 and analog/Digital I/O cards. The BASPA low voltage signal is output randomly causing the CPU to momentarily suspend RUN Mode (RUN Led goes Off and BASP Led goes On) and then go back to Run resuming operation without ever going to Stop Mode. It's annoying. I found it was the BASPA signal because, I programmed the Central Rack Power supply to trigger the fault Relay in case of Low Voltage fault (BASPA Low signal via BB-AA jumper). I thought this BASPA output was output only by the Power supply (6ES5955-3LF12), but I read somewhere that BASPA is also output by the CPU. I changed the CPU 946/947 for a new one but the problem persists. Who actually outputs the BASPA low signal? Is it the power supplies or CPs or some other module?

Help will be appreciated,