problem flicker BF S7-300

Hello onogram;

To add to Piscean's post, here is an article that points out the main cabling reasons that would cause a Profibus network to fail, from the main website dedicated to Profibus networks

https://us.profinet.com/top-5-reasons-your-profibus-network-failed/

If these tests do not help yu resolve the issues you are facing, you can try openng the diagnostic buffer of the CPU, in Step 7, while you are online with the PLC. Look for messages that refer to OB 86 and/or OB 122 in the buffer logs, they are most common when you have problems with a Profibus slave, Tell us (copy) what these messages show.

If you find it difficult to work with the diagnostic buffer, you can use the Save As.. button in the diagnostic buffer screen, and post the resulting text file here so we can have  a look at it, and help you resolve your issues.

By the way, have you checled whether the drive is also flashing a diagnostic LED when this happens on the CPU?

Hope this helps,

Daniel Chartier