SLC 5/04 program loss and 0001H error

Hi,
I have a SLC 5/04 processor, model 1747-L541 that had the backup battery fail a few weeks ago because we didn't see the BAT light on it in time, so we lost the program. I saw the FLT light when this happened, so I replaced the battery and then had to reload the program. At the time I didn't think to test the processor to make sure it wouldn't lose the program again, the BAT light went away and the program reload was happy.

Everything was running fine until last week when we had a power outage and again the processor lost the program. When the power came back on, I had a FLT light and no program on the processor. This time there were no battery issues. So I reloaded the program, but this time I tested the processor by shutting off power to it. It loses the program and gives me a FLT light. If I try to get online with the processor I get the NVRAM error code of 0001H. In looking at other forum posts, this sounds like a power supply issue but we haven't made any changes to this processor in years and until the battery went dead, we've never had a problem with it.

I have not been able to keep the processor from losing the program, so I installed an EEPROM chip on the processor. I've done this in the past and typically set up the processor EEPROM bit to reload from EEPROM only if there is a memory fault. But no luck, the processor would still lose the program and I'd have to get online with my computer and then reload from the processor EEPROM. I finally set up the processor so it always loads from the memory chip on reboot and that has fixed the problem for now, but its not a long term solution. This PLC stores user inputted ingredient names from an HMI onto the processor and assigns them to a group of silos that we have. We frequently move the ingredients in each of the silos or change ingredient names, so now if the old EEPROM program reloads after a power outage we may find that we have the wrong ingredients listed or have them shown in the wrong silo.

So today, I took a spare 5/04 processor that I had (model 1747-L542C) and installed it. I left off the EEPROM chip figuring I would be safe with the newer processor. To my surprise, the spare 5/04 processor had the same issue and is also losing the program and giving me a FLT code any time I cycle the power to the unit.

Short of checking the power supply module or replacing the rack, does anyone have any idea what might be happening or why this would suddenly start happening to both processors? I don't have any program errors that show up when I check the program, so I don't think it's a faulty program or incompatibility issue.

Thanks for any ideas in advance!
Cheers,
Curtis Holmes

Had this a few times, the first time it happened battery was good although did replace it, fitted an Eprom & no further problems on that system, had it happen on a couple of others, Eprom did not solve the problem replacing power supply & rack cured it for a year or so, I suspect that ageing components are the problem, it seems to be a common fault on the SLC, however, I did not find exactly what the problem was even i.e. if it was the processor, rack or PSU.
It did appear that the fault occurred when power was switched off or back on, it never happened on a couple of systems that were never powered down, My conclusion was probably ageing capacitors so power loss or re-instated caused spikes on the power to the rack/processor.

since it happened on 2 plc's
may i suggest the following and try this first.
turn off the pc, reseat all cards (plc as well) 2 or 3 times.
disconnect the power supply and do it as well.
do this for all comms cables.
with age, terminals get corroded and dirty, this will clean the terminals.

2nd - install a surge suppressor in front of the plc. we use corcom.
when the power is lost / brown out, the plc tries to store info into the memory while doing an emergency shutdown process. when powering back up, it tries to retrieve the info quickly. sometimes the process goes sideways and looses the program. that is why we use the filter.
hope this helps,
james

Thanks for the responses. Still sorting this out but gave me some ideas to try at least, I'll respond back on here if any of it worked.

Cheers!
Curtis

More than 90% of the time, a new power supply will resolve this issue. I can only think of one time when this symptom was caused by a faulty CPU, and one other time when there was backplane noise and a grounding issue. The other dozen or so times I have seen this over the past 20 years, the rack power supply was the culprit.

More about the EEPROM.

Akbrewer said:

I have not been able to keep the processor from losing the program, so I installed an EEPROM chip on the processor. I've done this in the past and typically set up the processor EEPROM bit to reload from EEPROM only if there is a memory fault. But no luck, the processor would still lose the program and I'd have to get online with my computer and then reload from the processor EEPROM.

Click to expand...

This should work, but you need to set the right bits to load from EEPROM in both the running program and the one stored on the EEPROM.

I finally set up the processor so it always loads from the memory chip on reboot and that has fixed the problem for now, but its not a long term solution. This PLC stores user inputted ingredient names from an HMI onto the processor and assigns them to a group of silos that we have. We frequently move the ingredients in each of the silos or change ingredient names, so now if the old EEPROM program reloads after a power outage we may find that we have the wrong ingredients listed or have them shown in the wrong silo.

Click to expand...

You can monitor S:5/8 with the HMI and tie it to an alarm to alert the user that the program was loaded from EEPROM. You can also allow the HMI to clear that bit if you so desire. That way, they acknowledge the alarm, clear it, and it is re-armed for the next occurrence. You could also modify the PLC code to make use of that bit to take machinery control precautions (drop out of Auto mode for example).

Problem fixed

Thanks to everyone for the suggestions on here. I tried everything James suggested on his first section (unplug and reseat all cards). That didn't work. So I changed out the main power supply on the PLC rack and that seems to have fixed it! I was able to take out the EEprom card and the PLC is now keeping the program as it should even when the power goes out.

When I looked at the circuit board on the old power supply, it has a slight brownish mark in one corner area of the board like something had shorted out or failed inside so maybe a capacitor or something on the board went bad, I haven't taken it apart yet to see what caused the discoloration yet but it was a 20 year old power supply. I'm guessing it was losing power too quickly before the PLC could store the program as parky suggested.

All of the SLC's seem to do this and it almost always is the power supply, change that and it goes away 95% of the time.



The other 5% start swapping out the analog cards in the rack, when they go bad (even though they are working) they can take down the backplane and short out the SLC battery when the power is turned off.


This is also one reason I try to never power down the PLC, I have seen machines where the PLC was powered with MCR/K1 power and had to reboot every time the machine was started again. I have rewired quite a few PLC's wired that way, just make sure the PLC checks that the power is on before turning any outputs on, and wire the outputs to MCR power.