Problem with Simatic 555

I have a machine running with a simatic 555 processor. We have tried two power supplies, three processors and are having an issue; the first processor ran for several years no problem until one morning everything shut down. Upon investigation we found the CPU good light off, the run light off and the battery good light off. A tech came in and got it up and running, he suggested the processor was having issues and gave us a trade for another 555. After running for a week and a half the trade out did the same thing. This morning, when replacement parts arrived I noticed the CPU good light on and was able to connect to the processor and was able to go online although the program was gone. After the initial comm I tried to upload the program and Workshop "failed to initialize." We swapped the power supply for a new one and have tried a 545 the tech sent up and still have no lights on the front and are unable to connect to the processor.
Any suggestions/ideas as to what we have going on here!?!?!?!

My first thought after what you have looked at so far would be a problem with the backplane (rack).

Just a little update; I was able to install the CPU in another rack and was able to go online and re-load the program. It would run for 10-15 minutes and fault out again. Each time I was successful in going online and found the PLC has had a "fatal error!" The fatal error each time has been "watchdog timeout." I changed the watchdog timer and changed the value from 500ms to 1500ms. This is a temporary fix at best and is allowing hours, instead of minutes, of run time.
Our thoughts here are of a problem with the backplane. A tech is supposed to be up this afternoon with a new rack, so hopefully we will see. Also the Kiln operator said there was some water in the bottom of the cabinet, so its evident it had to come in from the top of the cabinet and this could be the cause of the problem.

These devices are very tough however if you had shorts on the backplane there were taking out the CPU and Power supply it is very possible that the CPU is damaged now as well.

pct_jimmy said:

Just a little update; I was able to install the CPU in another rack and was able to go online and re-load the program. It would run for 10-15 minutes and fault out again. Each time I was successful in going online and found the PLC has had a "fatal error!" The fatal error each time has been "watchdog timeout." I changed the watchdog timer and changed the value from 500ms to 1500ms. This is a temporary fix at best and is allowing hours, instead of minutes, of run time.
Our thoughts here are of a problem with the backplane. A tech is supposed to be up this afternoon with a new rack, so hopefully we will see. Also the Kiln operator said there was some water in the bottom of the cabinet, so its evident it had to come in from the top of the cabinet and this could be the cause of the problem.

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As far as the wathdog timer From my experience with TI 505 make sure you have 2 End statements. If it doesnt and can continue to scan without ending the ladder, I cant remeber Exactly why it does this but it can.

Also you very well may have a backplane Issue. But when you cant get the PLC to show Processor Good, Turn off and remove the battery for a couple of minutes then return I have had to do this a # of times.

Best of luck...

randy741985 said:

As far as the wathdog timer From my experience with TI 505 make sure you have 2 End statements. If it doesnt and can continue to scan without ending the ladder, I cant remeber Exactly why it does this but it can

Click to expand...

We use a 545 processor for one of our plcs and it would randomly get the watchdog timer issue and shutdown and the end rungs were the problem. I cant elaborate on why but it caused this issue for me.

Thanks for the replies guys! The man who wrote the program is suppose to be down this week at some point (he is iced/snowed in @ North Carolina) so I will run this by him and see what he thinks. I'll be sure to keep you all posted on my progress.
Again Thanks!

The tech finally arrived today. We pulled the rack and found evidence of water damage on the backplane. The output card in slot 16 also showed evidence of water and had a blown fuse, it was a spare card and was not in use. We are going to see how it runs and hope that was the problem. We also found the conduit we believe the water was coming from and have hopefully fixed it so water can't enter the cabinet to prevent this from happening again.