Hi All,

I've been tasked with re-commissioning an old S7-400 control system. It has been relocated across the world and we have very little information on its last operating state. 

There is an S7 416-2 DP, which has about 84 micromaster 420 / 430's connected to it (split into segments, all within the control panel). We have a lot of bus faults, and have managed to remake connectors, replace comms interfaces, etc, to get down to "only" 14 with comms issues. 

As part of our trouble shooting, we have been using a Procentec ComBricks module, which has a RS485 oscilloscope function. 

In order to narrow things down, we have made up a cable - with new cable, new connectors between PLC, ComBrick and one drive (with new DP board on it). Fault is still there. On the ComBricks interface, when viewing the two oscilloscope readouts (PLC and the drive), it appears that it's the PLC that is distorted. 

Is it the case that the distorted signal in the image is of when the PLC broadcasts, and the clean signal of the slave is when it replies? 

If so, is there a problem with the PLC side of things rather than the slave?

We have replaced the PLC and replaced the PSU - the problem is still the same.

Another thing; the panel is powered up by a temporary generator - no power to the factory yet. 

What's next? Could it be backplane? 

Thanks.

Hello,

to my curiousity, it can be interesting to know what PB DP profile is set on cfg and especially what comm speed is set, due this number of slaves and also segmentation. Any Repeaters on bus? Your situation looks to me generally like some high power interference near Master PLC, in case you replaced some components for test. I expect you don't have any error on modules/CPU and also inside diagnostic buffer. Also your info about temp generator is intersting here because this type of device can be also big interference problem in my opinion.