Siemens make 135U

I have 135 U siemens make PLC and recently we have trouble of flickering of BVQ red led intermitently. Pl. tell me the reasons for troubleshooting this peculiar problem. Thanks and Regards

ajoyanjana said:

flickering of BVQ red led intermitently.

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BVQ?

Are you sure about that LED label?

Can you give us any more details as to your fault?

Does the CPU go into stop mode? If it does, have a look at the ISTACK, this will give you the reason why.

Have a look here for the manual for your CPU, this will give you details on how to use the ISTACK for fault analysis.

Paul

ajoyanjana said:

I have 135 U siemens make PLC and recently we have trouble of flickering of BVQ red led intermitently. Pl. tell me the reasons for troubleshooting this peculiar problem. Thanks and Regards

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Do you mean the QVZ LED ?

This fault LED typically indicates one of the analog or comm mudules is not responding.

Ian

Can you allow your plc to stop ? if so then delete all the error handling OB's from the plc and then let it stop when the error is encountered. As previously stated you can then use the stack to find the location of the problem.

If you can't allow the plc to stop you could create some code in the error ob's which would copy the accumulators and the stack into a DB (OB170 does the stack IIRC). You can then examine the DB to look at the accumulators and the SAC from which you can then work out in which OB,FB, or PB the error occurred in. I did this some time ago (in a 928B CPU ) to report just about every possible error OB message via a HMI without stopping the CPU.

The QVZ led flickering / blinking continues intermitently without stopping the CPU. The drives also runs for few minutes and stops without any sort of indications.

All the I/O modules were thoroughly checked and 3 nos. modules were replaced with new ones. Also, the Bus Modules ( 5 nos. ) were changed but the blinking / flickering of QVZ led continues.

Is it possible to program to detect the fault in the system or any other solutions?.

Thanks and Regards

Sorry for the incorrect information in my previous post (#4), I was in Step 7 mode where the CPU stops if the error OB is not present. In a Step 5 system the CPU can continue if there is no error OB present in the CPU, it depends what is programmed in DX0

To force the CPU to stop you to need to program a STP command in OB23 and OB24 and then examine the ISTACK when the CPU goes into stop. This should lead to you the access causing the timeout error. Note that OB23 is for peripheral accesses, OB24 is for the process image update. I read this in the 928B manual - you need to refer to the manual for your particular CPU

L D[AR2 said:

Sorry for the incorrect information in my previous post (#4), I was in Step 7 mode where the CPU stops if the error OB is not present. In a Step 5 system the CPU can continue if there is no error OB present in the CPU, it depends what is programmed in DX0

To force the CPU to stop you to need to program a STP command in OB23 and OB24 and then examine the ISTACK when the CPU goes into stop. This should lead to you the access causing the timeout error. Note that OB23 is for peripheral accesses, OB24 is for the process image update. I read this in the 928B manual - you need to refer to the manual for your particular CPU

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CPU 928B on 135-U Rack could not reset after re-loading of the USER PROGRAM. The slot address of all the signal modules are ok. The red LED BASP and STOP MODE red LEDS are ON. After overall reset the CPU goes back to RUN MODE without USER PROGRAM