E C Edwin

...Last termination is done at OP77. at the final Node, in Profibus connector ERR LED is ON and OFF only when the machine is started, ...

I have tried those connectors and only thing I can say is that those LEDs aren't much helpful, like there aren't.
I also have a doubt that adding aditional electronics on the line somehow influences the network, since the electronics itself has also a capicatance and for sure distorts signal.

But I can say if not all connectors are green, then something is wrong with your network. The protocol itself also repeats telegrams, you can see this in bus configuration, and corrects errors if a response comes within timeout.

The problem not necessarly is located near the connector you see the error, a signal may reflect from one part of cable and collide with other signal producing interference or wave node. At that part your equipment will fall off.

My recomandation:
- Disconnect all connectors,
- Cut out the cable wires, where was connection was done before
- make for sure the minimal length of section is at least 0.8m as needed from specifications
- on VIPA conector case, you will find a pin(spike) for holding the cable secure. Break them all with clamps, this is the mostly problem on that connectors, the spike damages insulation of cable.
- remount all connectros on cables

Regards