I've been working on a SLC 5/04 (L541) inhibiting some very strange behavior. You can power up the PLC, download the program, and it will work great. When you cycle power to the PLC it will come up with a solid red fault light with all other lights off, the PLC communications ports are completely unresponsive. On the second cycle of power the fault LED is flashing red and will allow you to redownload the program and resume normal operation.

The PLC has a new processor and has gone through numerous power supplies trying to fix it.

I removed all I/O modules from the physical chassis and created a program with only the correct processor selected. Same thing. First power cycle, solid red LED. Second power cycle, flashing red LED.

The grounding looks good, both to the power supply and the chassis. It has a good isolation transformer on the incoming power. You can see where they added a line filter, then surge suppression, and then a UPS trying to keep it from happening.

The only thing left I can think of is the chassis, but I thought I would check before I started swapping parts

Thanks
TW

Here is long shot:
Is there possibly an old EPROM in the SLC5/04 ? And maybe it has the bit set for "load always". And maybe there is something wrong with the program on the EPROM.
Try to remove the EPROM if its there. Remember to clear the bits for "load on mem err" and/or "load always". This just to see if the problem is related to the EPROM.

Apart from that, it could be a bad capacitor. The big one next to the memory card socket.
You can try to exchange the CPU. Even factory fresh CPUs can be defective.

Sounds like time to take this CPU to your test chassis. Need to see if the problem follows the CPU.

I changed the processor. There is no memory module in it.

TW
I am sure you have already got this by now, but we had the same type of problem on a machine in Dominican Republic. Only differece was, we always had a solid red LED. Never remember seeing a flashing LED.
We swapped everything, finally took another whole chassis from another machine that was in storage and replaced the chassis. This solved that problem. I did ship the chassis back to the office, and then when i got back, installed a processor, etc., same thing on the bench. Solid LED light, and faulted.

I'm pretty sure your right Kcor. I just hate to start swapping parts when I might have missed the obvious

TW
I had a powersupply smoke and got a new one. No problem right change the PS and go on. Wrong was I. 2 new PS later I noticed the 5/04 had a fault. We replaced the chassis all was good the CPU was fine we downloaded the project and off we went. Hope this helps.

Would a bad CPU battery lead to blasting away the program at power down/restart? I hate throwing parts at a problem in hopes of making things start to work, then you are stuck with a pile of good/bad/?.

We had a similair issue, the problem was that oil yes oil, had leaked from the old conduit onto the chassis (backplane) causing the same problem. It wasnt till I visibly saw oil on the back part of one of analog input cards that I found the problem.

You could also make sure its not looking for a EEprom to load from on Boot that isnt there:

Data File S2 under Memory Module Tab:

Memory Module Loaded on Boot S:5/8

Mabey the same chasis of kcor and Jak is doing the rounds and you have ended up with it....

Maybe we could get a good price for it if we posted it on Ebay as "Slightly Used"

A great selling point yes this chassis is “experienced” used only on 2 or 3 jobs.

Just a thought. Make sure these numerous power supplies have all been set to the right incoming supply. I"ve seen (done) that before and experienced very similar problems.

i would also make sure this is not a software or configuration related issue...This might sound strange but i had similiar problem se before when i had a third party module in the chassis and the SLC controller kept faulting when i first power up since it can't get response from this module...I would disable any supscious modules or codes before starting swapping things...