AB SLC5/01 CPU Fault

[henno2000]

Hi, I am after a little help if possible?

I am unfamiliar with AB processors/software, but was asked to look into a 'CPU Fault' that was flashing.

After connecting to the PLC, I checked the diagnostics and from the RSLogix 500 software, the only thing that appeared abnormal was the fact that the following status was indicated:

Fault/Powerdown Rung#S:20 (12)

After searching the menus I tried clearing the fault etc, but nothing seemed to changed.

Reading the online help did not present anything, and I could find no reference to a '12' block anywhere in the program.

I tried the various programming modes and also tried changing some of the variable in the diagnostic screen, but to no avail.

If possible, could some indicate what this error means, and if it is possible to remedy/locate the problem (assuming it is located in the PLC it self)

Regards,
henno2000

 

[lhopper]

it's been a while since I looked at a SLC-5. I think the S:20 is the day register in the porcessor. Some rung is trying to offset the the day register by a value that exceeds the boundary (the # in front of S:20 looks like an index address)

 

[lhopper]

do a search for S:20 or S:[
there is an instruction that is causing the major fault.
check the processor status, go to the errors tag, clear major fault.

 

[Mickey]

Note S:20 is not available in a SLC5/01. Where are you seeing the status?

Can you post your .RSS file after a upload with fault still active.

What do you see under the error tab in the processor status?

 

[henno2000]

@ lhopper: I have tried all options such as clear major fault etc (in both online and programming modes), but nothing appears to happen.

@ Mickey: I shall send a screen dump of the error screen tomorrow when I get to work. I shall also try to obtain the .RSS. (FYI, in the error screen the value displaying the S20 fault is greyed out - IE: not editable)

Regards,
henno2000

 

[henno2000]

Hi,

I have now managed to clear the fault. It took repeated attempts at downloading and running.

Another problem has occurred.

To activate the start output, a series of condition has to be met, which is activated by the start push button.

This should then set a coil to latch a binary output.

This is not happening when viewing online.

I can see that push button input, but the output is not latching (or even coming on when the push button is held on)

Could anyone suggest anything as this has me totally baffled. (Looking at the simple logic, it should start). Are there any registers which need initialising due to the fact that I have performed a new download to the CPU?

I have attached a copy of the program for reference. (The part I am referring to is located in LAD5 NW1)

Many thanks in advance
henno2000

 

[OkiePC]

Don't laugh, but did you put it in run mode?

In the program ladder 5, are you looking at rung 1 for B3:0/4 to latch? If so, I:5.0/12 must be off. In the copy of the program you posted, it is on...(remote selector switch...)

 

[Ron Beaufort]

see if the notes (attached) help ...

PS Edit ... well, my distinguished colleague, OkiePC, was quicker - but then I took time to draw a picture ...

 

[henno2000]

Don't laugh, but did you put it in run mode?

In the program ladder 5, are you looking at rung 1 for B3:0/4 to latch? If so, I:5.0/12 must be off. In the copy of the program you posted, it is on...(remote selector switch...)

Ha! Yes, the CPU was definitely in RUN.

Going online with the CPU, the remote selector switch input (I5.0/12) had a green line through it (active) which I assume to be correct because you need all contacts to be in this state to activate the output.

 

[Ron Beaufort]

going deeper (between customer calls) ...

check the DOC_LEV_HI bit (N9:0/6) in the next rung ... looks like it's UNlatching your output as soon as it's Latched ...

 

[Ron Beaufort]

personally I'm wondering about that "fault" message that you reported earlier ... if something like that happens again, check the screen shown below and try to capture it before you clear the fault ...

 

[henno2000]

check the DOC_LEV_HI bit (N9:0/6) in the next rung ... looks like it's UNlatching your output as soon as it's Latched ...

Thanks for the advice, will give it a whirl. (Although N9/0.6 cannot be located in the program, I think it may be a reference to a PLC input that was connected via a wireless link which no longer exists. This could have defaulted to set value when the program was downloaded.) I assume that this value can simply be toggled?

Also, out of interest, could anyone explain what the first three rungs are doing in LAD2?

Regards,
henno2000

 

[JBJennings]

Could be anything, possibly message trigger bits for HMI????

N19:LAD# is first rung in each ladder file?????? To let programmer know which ladders are running?????

 

[Ron Beaufort]

N9:0/6 is being controlled (along with all of the other bits in word N9:0) by the WORD operations used in Ladder 3 - Rungs 15 and 16 ...

as for your question about the first three rungs:

I'm going along with the idea proposed by JBJennings ... the pattern is repeated at the top of (most of) the other Ladder Files ... and the addresses being used correspond (pretty much) with the numbers of the various Ladder Files ... note that "pre-scan" would turn all of these OTE-controlled bits OFF each time the processor enters the Run mode ... then, if (for some unknown reason) a particular Ladder File (subroutine) was never scanned, then the appropriate bit would stay at a ZERO (off) status ... not sure WHAT (if anything) is monitoring those particular bits – but I'm pretty sure that the "has-this-subroutine-been-scanned?" idea is behind what we see here ...

 

[henno2000]

check the DOC_LEV_HI bit (N9:0/6) in the next rung ... looks like it's UNlatching your output as soon as it's Latched ...

Correct. This input was ON. Must have defaulted to this when the download was performed. It is no longer used and so has been removed.

Many thanks for the help