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Rack failure OB86 problem

11/3/2008 9:41 AM	Rate (0)
Temo Posts: 2 Rating: (0)	Thanks a lot for your co-operation. The problem we have as as follow: * Our network is composed of31 node (Siemens distributed I/O modules) connected to CPU/414-3DP through a Diagnose Repeater f. * The problem is that some times the CPU lose the communication with one of these nodes and thus we have a rack failure OB86 error and the production line is stopped as the inputs or outputs are not seen by the PLC. And we can determine the address of this node using S7 diagonistics buffer. * The problem also is that the losing node is differ every time (which mean that if nowadayes the losing node mayhas the address of 25 , tomorrow it may be 30 or 31.. or any other node addresses and all the time we have a production line stop. We have make the following without any effects: * Changing the PLC CPU * Changing the repeater * Changing the cable connecting the CPU, the repeater * Adding repeaters to some places in the network * Checking the connection for all the distribued I/O modules. But we still have the same problem I hope the previous informations are helpful to you to determine our network problem and we are waiting to receive from you. For further information kindly contact me
Temo Posts: 2 Rating: (0)
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11/3/2008 11:44 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Dear Temo, well, this sounds like serious problems you have at your network. I think what is always useful to check is the following. Check the Grounding on each entry and leave of the cable in every cabinet. Check the Grounding of each PROFIBUS connector used. Did you already check the diagnostics of your diagnostics Repeater used, did this device monitor any disturbance at the network? If all that is not solving the issue and you do not want to use the OB 86 to prevent the PLC from going to stop you may have to get a PROFIBUS specialist on site to measure the PROFIBUS with an oscilloscope. They may measure the disturbance or find any relation between the PROFIBUS running and the upcoming fault... sometimes really strange things are the causes for the faults... I know about trains passing... causing Problems. I hope we will find a solution. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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11/4/2008 7:45 AM	Rate (0)
Temo Posts: 2 Rating: (0)	Thanks Mr. J_Bell for your co-operation. I have already checked the grounding of the modules several times. For the repeater how can i check the diagonstics of the repeater and can i do this using the ethernet network to look the hardware configuration of the network in S7 and what do you expect to find especially that i have no problem nowadays but the problem may appear at any time. Thanks and have a nice time
Temo Posts: 2 Rating: (0)
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11/4/2008 8:17 AM	Rate (1)
umencho Grandmaster-Expert Joined: 3/21/2006 Last visit: 1/10/2026 Posts: 10247 Rating: (1183)	Hi See in manual : SIMATIC Diagnostic Repeater for PROFIBUS-DP ( chapter 7 ). And maybe this FAQ: What are the requirements for using the "Prepare cable diagnostics" function? regards

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