SLC 500 losing program after cycling power

Hello there,
I am new to your site so please excuss the inexperience. I have a SLC 5/04 that loses its program everytime we cycle power on it. This processor has no eeprom installed and we have replaced the battery. We have even tried a new 5/04 and still have the same issue. I have been given the task to eliminate this problem and I am wondering if anyone here has run acrossed this themselves. Looking in the program status bits S:1/12 is set high.
Any information would be appreciated.
Thanks

that bit tells the processor to "Load Memory Module and Run" ...

since you don't have a Memory Module installed, I'd suggest that you try turning bit S:1/12 OFF (make it a ZERO) and try doing a power cycle again ...

while you're at it, you should also check the status of bits S:1/10 and S:1/11 too ... all three of the bits mentioned are associated with controlling how the Memory Module is used ...

incidentally, I just tried an experiment with a spare SLC-5/04 in my lab - and setting JUST bit S:1/12 to a ONE status did NOT result in the "lose the program" problem you reported ... I'll try some more experiments after lunch ... can you post the RSS program file? ... you'll have to ZIP it first to attach it to a forum post ...

and welcome to the forum ...

I've tried several more tests using a spare SLC-5/04 system in my lab and (so far) I still haven't been able to duplicate the problem you reported ...

question: are you SURE that you do not have a memory module installed in your processor? ... I'm betting that you ARE sure - since it would be hard to miss it if you replaced the processor as you indicated ... but - we still need to know for sure ... please ask if you're not SURE how to tell ...

question: can you ZIP and post the RSS program file? ... don't get yourself in trouble with the boss - sometimes this material is considered to be "trade secret" or "proprietary" information ... but if you ARE allowed to post the file, it might help us troubleshoot your system ...

one other question: HOW are you "power cycling" the power to the processor? ... by any chance are you simply throwing a main disconnect switch (example: 480VAC or 240VAC) to an electrical panel? - or are you doing something a little more "graceful" than that? ...

idea: sometimes throwing the main disconnect results in a high "power spike noise" condition - related to the "flyback" effect from a control voltage (480-to-120) transformer ... if that's the way that the power is being cycled, then all bets are off on what the processor is going to do when the power is finally restored ...

also ... is the processor connected to a UPS system? ... if so, how much did you pay for the UPS? ...

idea: some "low end" UPS systems produce a high voltage "power spike" condition when they switch over from a "charging on line power" to a "providing backup power" condition ... specifically, a cheaper UPS can sometimes CAUSE more problems than it SOLVES ... I doubt that this is your problem - since you'd have to go out of your way to "power cycle" the processor with a UPS installed - but I just thought I'd ask anyway ... the more we know - the better we can help ...

Hello Ron,
Thanks for getting back with me; I have read many of your replies pertaining to other PLC issues and I appreciate you helping with mine here.
I have checked s:1/10 and 11 which they are both set low. When I tried to upload the program it says that the file exceeds the foum's limit - the zipped file is 611.2 kb.

Ron,
To answer your second reply - no, there is no memory module installed - if this is the module that plugs into the main board of the processor next to the battery.. In regards to the question of how they power down the PLC/cell - I do believe that it's the main disc that they throw. This is the way that they have done for years (not saying it is correct) but without PLC problems on the other machines. We do not have an UPS installed with any of our PLC's - an issue I will be looking into.

I think that I remember having this problem once, and the solution was to change out the power supply on the SLC... Sounds weird (with a new battery). If you have spares, I would try changing out the power supply and the CPU. I bet that it is one of the two.

-Brian

Your SLC power supply could also be the culprit. But before you go down that road lets talk about grounding.

Is the SLC chassis grounded? Is there a copper ground attached at one of the SLC chassis mounting tabs?

Our NJ plant had the same problem with three SLCs. They couldn't find it and asked for my help. They tried everything, including changing processors and power supplies. I asked AB and grounding was one of the things the tech I talked too suggested. I passed on the suggestion and the NJ plant engineer scoffed at it. I flew to the plant several months later on another matter but I found out that not only was the chassis not grounded, the control panels were not grounded either. I ran a temporary ground and also landed a copper ground wire on the chassis mounting tab, not relying on the backpan to be the ground. The plant engineer about had a heart attack when I threw the disconnect off. But when I turned it back the PLC came back up with the program intact. I cycled it several times just to make sure.

That may or may not be your problem, but it sure won't hurt you to check.

I will check the grounding question when I go back in and get back with you. Thanks for all the input guys. I will repost what I find whenever I check it out Monday.
Thanks

I will try the power supply after I check the grounding issue noted by Alaric. When we replaced the processor we also put in a new battery which did not help.

definitely check out the excellent suggestions from my distinguished colleague Alaric about chassis grounding and the power supply ...

one more link in the chain that hasn't been mentioned yet is the chassis ... this isn't the most "likely" culprit - but if it is indeed the problem, then nothing else is going to solve it ...

also it would be a good idea to read the following recent post about the size of your RSS file ...

http://www.plctalk.net/qanda/showthread.php?p=371626&postcount=4

please let us know what you find out ...

Even a new battery can be a dud. Try swapping it with one of the known good PLCs. Next try the whole power supply.

from ydtech:

Even a new battery can be a dud. Try swapping it with one of the known good PLCs. Next try the whole power supply.

Click to expand...

well, that's another thought ... is the battery LED lit up on the processor? ...

and just for discussion, the battery on my lab processor has been disconnected throughout all of the tests I've mentioned above ... I usually leave all of my processors' batteries disconnected to keep from draining them when I'm not teaching classes ... even so, with an SLC-5/04, the "keep-it-alive-while-I-swap-the-battery" capacitor will usually maintain the program in memory for hours - if not days ...

so - how long are these "power cycles" lasting? ...

Another idea while the grill heats up...Try wiring another power source to the SLC and cycle the power to see if it is the current power or something in the SLC.

HTH

and yet another: most SLC power supplies have a "user connection" under the front door that lets you make use of the supply's 24VDC output for I/O devices, etc. ... are you using that connection, and if so, how heavy (amps) is the load which is connected there? ... and is the load resistive, inductive, or something else? ...

Another vote for the power supply

Had the EXACT same issue with a 503.... I'll cast another vote for the power supply.

That thread should be findable by "search"ing this forum.

Stationmaster