Hello ICSramzi;

Based on the tables in this manual page (the S7-400H System Manual), depending on the frequency of the flash of the Stop LED, it signals either a request for a memory reset or that there is a RAM being conducted:

https://support.industry.siemens.com/cs/us/en/view/82478488/34700969611

In both cases it has something to do with RAM memory. You have no RAM memory card in the CPUs as you mentionned, but there is a small amount of RAM memory on the CPUs that must be supported by a battery on the Power Supply module (lift up the front cover); do you have one on each of the PS modules in your setup?

I also suggest you open the diagnostic buffer of each of your CPUs (with Step 7) to find out what the operating system has detected, causing the Stop LED to flash. The diagnostic buffer often provides hints on the cause of such a problem.

One recommendation: download and save the S7-400H manual and keep it close-by, when working with these CPUs, it is sn invaluable source of information and troubleshooting methods with redundant systems.

Hope this helps,

Daniel Chartier