Identifying faulty module in rack from OB86

We have identified a faulty module DI module which causes PLC to go on STOP (as programmed in OB86). 

By trial and error in the specified rack, we found it was DI module 24 V DC 6ES7 131-4BF00-0AA0. It was in slot 9 of rack 4.

We found out which module by trial and error - swapping one module at a time until the problem stopped. We were able to confirm problem by putting faulty card back in.

But this takes a lot of time, assumes that only one module is faulty … and surely the diagnostics have a way of detecting the specific problem?

So next time we have a similar problem, we would like to diagnose it faster and more intelligently.

From diagnostic buffer of CPU, it was clear problem was in this rack, but which module was not specified. While I see that this DI module does not support diagnostics, I was hoping that somewhere we could find the information on which module in the rack was causing the problem.

Looking at OB86, we had B#16#39 with B#16#C4: Failure of a DP station

From the HELP for this type of fault, it says:

OB86_MDL_ADDR: Logical base address of the DP master · 

OB86_Z23: Address of the affected DP slave:

-               Bits 0 to 7: No. of the DP station

-               Bits 8 to 15: DP master system ID

-               Bits 16 to 30: logical base address of an S7 slave or diagnostic address of a       standard DP slave

-               Bit 31: I/O identifier

Here is the content of OB86_Z23 (which is held as an array 0-31 as recommended) in order [0],[1]…[31]. Leftmost position is array element 0, which I believe corresponds to bit 31:

1 110000010111111 10000000 00100000

It took me a while to figure out how the structure might work, and I would appreciate if someone could confirm if I am correct.

It seems that the ordering of the bits compared to the array structure takes quite a bit of manipulation - which is why I have my doubts !

Right hand block is bits 0-7, and the order has to be reversed. So 00100000 is bits 0-7 (in that order) so has to be reversed to give 7 to 0 so is 00000100 which is decimal 4.

So this is the number of the DP station, rack = 4

Next block from right is 10000000 for bits 8 to 15, which must be reversed to give 15 to 8 00000001 which is decimal 1.

Which is the address of the Profibus master system

These correspond to the hardware configuration (see attached screen shot).

Up to now, no extra information which is not contained in message of diagnostic buffer.

What I cannot understand is the meaning and ordering of bits 16 to 30 – can someone hep me please?

Is there something in here which helps us to identify which module in the rack is causing the problem?

It is 15 bits, so it must have some important significance … I just do not understand it.

Bit 31 is 1: what does this mean? If it was 0, what would it mean?

The goal is to use OB86 to identify which module in the rack is causing the fault.

I have a higher level question aside from understanding the detail of OB86: I am wondering if the system is capable of telling which module in the rack 4 has the fault.

 I have attached Word do with screenshot of hardware, diagnostic buffer message and content of DB86 (which holds values generated in OB86).

I would really appreciate your help in understanding OB86 and using the system intelligently to identify which module in the rack is causing the problem.

Thanks in advance,

John

Hi,

Take a look to the Excel file attached.

If you want to know which slot is in fault and display it on a panel for example, you have to list all diagnostic addresses from your hardware configuration and make comparison in your program to determine where is located the error module and set a variable with the slot number.

Example :

L AddressDiag_OB86Z23  //Address extract from Z23.

L 2045     //Diagnostic address of module slot 9.

=! F

SPB LB2

L 9

T SlotInError    //Tags representing slot in error.

BEA

LB2 :  TAK

L 2044     //Diagnostic address of module slot 10.

=! F

SPB LB3

L 10

T SlotInError

....

Hi, 

https://support.industry.siemens.com/cs/document/29338956?lc=en-WW  find the sample program in this link which gives you the complete diagonistic data of a module..

New question published by Iosif is split to a separate thread with the subject Can I identify which of DI/DO is faulty?.

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New question published by omicron_theta is split to a separate thread with the subject How get information from OB86_Z23 where communication error occurred?.

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