Diagnose hardware issue on Profibus Rack with 11 x DI818?
We are working on a system that uses Redundant Profibus(CI854A/CI840) to connect to its remote IOs. We have a total of 5 racks 4 of which are working smoothly. The system is made of Redundant PM864.
The rack (2nd) that we are facing an issue on does the following:
It is supposed to have 11 x DI818 modules working in Simplex configuration.
As long as only the first 7 modules on the rack are connected, everything works fine. However, on addition of the 8th module our secondary Profibus module goes in fault.The primary still operates in R(un). On giving a power cycle to the rack, it behaves abnormal. Some cards power up correctly while some go in fault.On the CB, the rack goes in fault; but the profibus CI840 remains in warning.
We have done the following:
1) replaced the MTUs and Cards on the rack.
2) We have a completely same card configuration on another rack (1st Rack) . We swapped the profibus configuration between the 1st and 2nd Rack and the problem still persisted with the 2nd Rack.
3) We disconnected all Field IOs from the MTUs and kept only L1 & L2 (+) (-) connected.
4) We swapped the profibus cables between Rack 1 and Rack 2 but the problem still persisted with Rack 2.
I understand that it must be a hardware problem; any input how to tackle this problem or on any configuration that I may have overlooked would be greatly appreciated?