CompactLogix has stopped running, FUSE indicator is on

[defcon.klaxon]

Hi all,

Got a call from a client just now, apparently his remote well site stopped working so he has it in hand. He sent me photos of the PLC (1769-L24ER-QBFC1B) and the RUN light is not illuminated, but next to the High Speed Counter indicators the FUSE indicator is illuminated. Had him switch the PLC from REM to PROG to RUN to REM, still not executing code.

I did some quick searching and have heard that this is not field repairable, is that true? If so, yeesh. But looking through the user manual I can't seem to find any info on what this fuse indicator is meant to convey, and what could cause it, and how to prevent it in the future.

I'll keep searching but thought I'd post here as well. Thanks for any help.

 

[soultrader]

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um006_-en-p.pdf

 

[Ken Roach]

Thanks for specifying the exact module and position of the indicator. Don't confuse this feature with the non-repairable physical fuse that protects against catastrophe on the Field Power bus of a 1769-L1 controller.

The High Speed Counter features of the 1769-L24ER-QBFC1B controller are basically a permanently installed 1769-HSC module. The 1769-HSC has an electronically resettable overcurrent protection feature on its outputs.

User Manual for 1769-HSC with Overcurrent protection description: https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1769-um006_-en-p.pdf

You can configure that feature to attempt automatic reset, or set an "RBF" bit to Reset Blown Fuse in the Output table.

I don't know if a power cycle will clear it, or if a power cycle + program reload will clear it.

 

[defcon.klaxon]

Hi all,

Thanks for the quick replies. So this is odd, I am not using the High Speed Counters at all, so why this fuse has blown I don't know, and why the logic refuses to run I don't know either.

Ken, power cycling does not clear it. I'll take a look at the literature you provided, thank you.

Also thanks for the link Soultrader.

 

[defcon.klaxon]

OK so looking through the system tags, I see Ch3:O.ResetBlownFuse; is it as simple as changing that bit from 0 to 1?

 

[Ken Roach]

I've never dealt with that feature before so I'll just be guessing.

My reading of the user manual is that yes, setting the .ResetBlownFuse bit in the Output tag should reset the overcurrent protection feature and the FUSE LED should extinguish.

You are right, of course, that the overcurrent feature on the HSC shouldn't fault the controller or halt execution of the user program.

So it might be an incidental indication of other physical damage to the controller. That ain't good.

 

[defcon.klaxon]

Thanks Ken, yeah I was just going to say I see no indication that the HSC fuse would halt the entire PLC from executing code, which of course makes me worry about the potential for damage elsewhere. Which would be quite odd, this particular site is in the northern central valley of California and we haven't had any lightning or etc, so what would have caused this issue is worrisome.

I just took another look at the photos the operator sent me and the OK status indicator is solid red, indicating that there is a major, unrecoverable fault. It'll be interesting to see if I can go online with the controller and see what's up. Fingers crossed.

Thanks guys!

 

[defcon.klaxon]

Update on this, went to the site today and the controller was BRICKED. Solid red OK light, link lights on the ethernet jack were off, wouldn't show up on USB either.

Tried pushing the reset button with a paperclip (below the RUN REM PROG switch), nothing there either. This controller is totally dead.

Can this unit be refurbished? Would Allen Bradley do that, or a third party? If I recall, the unit was installed in 2019 so it's not old.

 

[JaxGTO]

I don't know if a $2400 controller is worth trying to fix. I had that electronic fuse indicate on one once, but it cleared with a power cycle.

 

[Haus]

Rockwell does have a repair program, pricing depends on how fast you need a replacement. They do same day exchange or repair

 

[Firejo]

Before throwing another controller at it, I’d have someone do a very thorough inspection of the installation. It sounds like the processor was hit with some sort of surge and it would suck if it happened again.