HELP! Allen Bradley SLC 5/05 fault

You said the fault light was flashing. If so, the controller did not lose the program. If it had lost the program the light would have been solid red.

The controller had a fault, but because the program was re-downloaded, the specific fault code has been lost. So we don't know what the fault actually was. So this very possibly could reoccur.

In desperation, if this scenario ever occurs again, turn the keyswitch to Run, then Program, then Run. This will clear the fault and the controller will try to go back in to run mode. It might just fault again, but possibly if that fault condition does not still exist you might be able to get up and running. On most controllers doing this will wipe out the fault code on other newer 5/05 controllers they will keep the fault code stored so you can find out what the fault was.

The optional EEPROM can be configured to reload the program automatically on a power cycle. It actually has three options.

1. Reload on every power cycle.
2. Reload only if the program is missing/corrupt
3. Never reload automatically. Only will reload if the user via RSLogix software triggers the reload.


OG
 
If its in a hot environment or with electrical noise or if its just old and seen better days (like me :) ), do you know what the series is A,B,C or D? that will tell you the age

I do not have that series# off hand. It is in a clean electrical room that is temperature controlled so it is not unusally hot or humid in there.



You said the fault light was flashing. If so, the controller did not lose the program. If it had lost the program the light would have been solid red.

The controller had a fault, but because the program was re-downloaded, the specific fault code has been lost. So we don't know what the fault actually was. So this very possibly could reoccur.

In desperation, if this scenario ever occurs again, turn the keyswitch to Run, then Program, then Run. This will clear the fault and the controller will try to go back in to run mode. It might just fault again, but possibly if that fault condition does not still exist you might be able to get up and running. On most controllers doing this will wipe out the fault code on other newer 5/05 controllers they will keep the fault code stored so you can find out what the fault was.

OG

yes, the FLT light was indeed flashing. From my research, it seemed to indicate the program was lost, and the programmer my local distributor sent out was confident that the program was lost. He did not think the hardware had a problem. But maybe we are all wrong?

The key switch was in the REM position. We flipped it to PRG and then to RUN. The Run light was flicker on for a second, then the FLT would begin flashing again.

We will continue to watch it closely, and thanks for all the input.
 
If the light went to Run, even just for a moment, the program wasn't lost. Totally understandable that it would fault again. That tells me there was a program problem causing the fault.


OG
 
You said the fault light was flashing. If so, the controller did not lose the program. If it had lost the program the light would have been solid red.

OG, I know you have forgotten more than I will know but I disagree with that, flashing is just faulted and is recoverable and can be from MANY reasons and one is loss of program... example is the battery is bad and the PLC is powered off (for some time) the program will be gone and the fault light flashes or if you factory default a processor the fault light will flash

Odds are the power supply is having issues and will short out the CPU and make the program disappear, this I have seen more than once

In desperation, if this scenario ever occurs again, turn the keyswitch to Run, then Program, then Run. This will clear the fault and the controller will try to go back in to run mode. It might just fault again, but possibly if that fault condition does not still exist you might be able to get up and running. On most controllers doing this will wipe out the fault code on other newer 5/05 controllers they will keep the fault code stored so you can find out what the fault was.

This will only work with a minor fault not a major... but its worth a try
 
Yes there are multiple possible causes for a flashing red CPU light. Far and away, the most common cause is a program error causing a fault.

Flashing red does usually indicate it is a program fault and that it is recoverable. But there are exceptions. Solid red means it is not recoverable and the program must be reloaded. That one holds pretty much true across the board.

The keyswitch trick works on all Rockwell PLCs and will clear a MAJOR recoverable fault. Minor faults do not shut down the controllers though they can lead to major faults which will. The key switch does not affect minor fault bits.

Couple idiosyncrasies on the key switch:

The Logix 5000 requires the switch to go PROGRAM-RUN-PROGRAM whereas the PLC-5 and SLC 500 require RUN-PROGRAM-RUN

Toggling the key switch on the PLC-5 and Logix 5000 will not wipe out the fault information but will wipe it out on the SLC 500. Newer SLC will retain the fault code but not the file:rung information.

OG
 
Solid red means it is not recoverable and the program must be reloaded. That one holds pretty much true across the board.

Solid red is a non-recoverable fault sometimes you can cycle power or short out VBB and GND and get it back so you can get comms again but you can not communicate to a solid red CPU the fault light has to be out or flashing for comms to work, from all the ones I have seen.

I flash about 3-5 5/05's a week and have seen a lot of errors on them
 
Be prepared for it to happen again. The likelihood that this was a one time occurrence is low (possible but low). As already stated there are all kinds of reasons why the processor went into fault mode a lot of which would be fixed by re-downloading the original program. Even if it was something as simple as a math overflow, re-downloading the program will fix it. If (or when) it happens again, before re-downloading see if you are able to go online with it and see what the fault code is. That will give you a direction to start looking for the root cause. If it is caused by the program being lost, that's bad news and is an indication of a hardware failure. I've seen more than one SLC rack cause the processor to dump its program and most of the time it was a couple of days or weeks between failures.
I'm glad you got the system back up and running but don't let your guard down, it may not be over.
 
Be prepared for it to happen again. The likelihood that this was a one time occurrence is low (possible but low). As already stated there are all kinds of reasons why the processor went into fault mode a lot of which would be fixed by re-downloading the original program. Even if it was something as simple as a math overflow, re-downloading the program will fix it. If (or when) it happens again, before re-downloading see if you are able to go online with it and see what the fault code is. That will give you a direction to start looking for the root cause. If it is caused by the program being lost, that's bad news and is an indication of a hardware failure. I've seen more than one SLC rack cause the processor to dump its program and most of the time it was a couple of days or weeks between failures.
I'm glad you got the system back up and running but don't let your guard down, it may not be over.

Thanks Firejo,

This was kind of my gut feeling, that we may be seeing this again.
 
Very often the culprit is the "Math Overflow Trap" bit, S:5/0.

Even if the original programmer had trapped arithmetic overflows after important instructions, that bit will be set on, and if it is still on at the end of the scan of file 2, then the processor will fault as described.

Arguably the worst "feature" they built into the 500 series, and it's the only series with it in.

I would advocate putting an unconditional OTU S:5/0 as the last rung of ladder 2, at least you'll still have a functioning PLC, which might be behaving badly, rather than one that's just put its hands up and said "I'm outta here !"
 
The plc was working fine up until about 3 hours ago. It was installed in 2005 or 2006 customer says.

Next time you get to site, take a can of spray contact cleaner with you....

1. IMPORTANT ! turn of the SLC power

2. in turn, pull each module out of the chassis

3. spray the backplane connectors with the contact cleaner

4. put the module back in, pull it out again, put it back again (2 or 3 times should be enough)

5. do this for ALL modules

As stated the SLC range REQUIRES all its I/O modules to be present and correct, or it will fault as described.


I had a similar scenario last year with a ControlLogix ControlNet module that was reporting faults, happened 3 times in one week. It had been in operation for about 13 years. I cleaned the contacts as above, and it has been working fine since (Of course I did all the modules while I was there !).
 
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According to Murphy's law, this processor died again Saturday night, but this time the red light was solid. The programmer again came in and found an 'Internal Software Fault' He deemed the best would be to simply get a replacement processor. But they did not have one on the shelf and Rockwell was closed for the weekend. He was able to get the running again, but it faulted a few hours later again. He found a spare at their shop and installed that one to they can get a correct replacement in.

With this fault, would you still recommend to clean module connections, manage network traffic etc? I suppose that would still be a good idea, but could that still be a cause of this fault?
 

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