RSLogix 500 OTE not behaving correctly

[Stampy 0]

Hi Everyone,

I am supporting a system which runs on a SLC 500 (1747-L532). A fault has developed whereby the output state of some digital outputs do not change within the ladder logic. Basically, on a rung, an XIO controls an OTE. When the XIO is high the OTE should be also high, however the OTE is not changing state. The OTE is only used on this 1 rung within the program and the routine is being scanned. I have trended the XIO bit to confirm no oscillation and at a trend refresh rate I cannot see any change of state. The XIO is controlled via a compare instruction which is stable.

I have plugged out the comms to the machine HMI to confirm nothing is being written from the HMI that may be causing the issue. I have also tried another processor from spares but issue remains. 

Is there something very simple I could be missing here?

All suggestions appreciated. 

[ElectronGuru 81]

You're showing three ladder files: File 2, File 28, and Pumps. Are you sure that all three of those are being scanned? Are there JMP/LBL or MCR sets being used in File 2 or Pumps? You're sure you've saved any recent edits and the Cross Reference Report is up to date; no sneak bits lingering further downstream writing a zero back to the output after this rung has been scanned?

Just for grins, create a temporary branch rung around the existing XIO N30:6.8. On the new branch, grab an unused B3, put it on an XIC, and manually toggle it. Probably won't make a difference but that will point more directly back at code scans being the likely problem. 

It's been a minute but I believe the Logix500 has "Test single scan" and "test step" modes where you can run the code one full scan at a time, or step through code the code one rung at a time. If it's not something obvious that we can't see from your pics, you might try that to see where you're getting hung up. 

Hope this helps. 

[Mickey 71]

Post the .rss file. 

[BobLfoot 302]

also check you cross ref and make sure you don't have a mov or clr of O:6 or O:6.0