Slc 5/04 not holding memory

[Mircopolo]

Servicing PLC with 5/04 processor. It was displaying BATT error and program was gone. I replaced battery, reloaded program put it in Run mode.
Everything was fine until power got interrupted. After restoring power Fault alarm has been displayed and program gone. Connected to processor and reloaded program back. Everything got back on track, no alarms or faults.
Processor was in run mode and communication was fine in both channels (RH+ and serial). To test what happened I intentionally turned power off.
Same thing happened. Fault alarm and program gone. I’ve connected to processor over RS232 and check errors status. In error description window it says “Unexpected hardware watchdog timeout or an ASIC reset occurred.”
Battery Low S:5/11 is set at “0”.
“Clear Major Error” reseted all and I was able to dawnload program again but if I take power off it will do the same.
So I don’t know if it’s problem with ASIC (I am not familiar with this) or processor is bad.
I tried two new batteries so that isn’t problem.
Will appreciate your support and suggestions.

 

[scott.lawrence]

https://control.com/thread/1026220643


try this thread...


more specifically;y, the post about replacing the power supply

 

[OkiePC]

I agree with the power supply being the likely culprit having seen those same symptoms cured once by replacing it.

 

[Mircopolo]

Big thanks to you guys, I followed your advice and after replacing PS everything seems to be fine.
Totally didn’t expect this because to my understanding battery should keep processor memory regardless of existing or nonexistent power source.
But working with control for so many years, I learned to believe in strange things existing even so you can’t see or comprehend them - when you experience one.
Thanks again Scott and Okie!

 

[OkiePC]

The theory is that as some capacitor ages or fails within the power supply, when it shuts down the voltage to the CPU falls off gradually instead of sharply so the PLC doesn't properly go into its shutdown process and wipes itself as a precaution. I might be wording this entirely wrong, but that is what we were told way back when I saw this issue some ten or more years ago.

 

[Ken Moore]

The way it was explained to me, or at least the way I understood it is:
When the power to the Rack power supply is lost, it notifies the CPU, so that it can stop processing and activate the battery backup power source. The Battery is only used when the power is off, so there has to be a switch. I was told that once the signal is sent, the powersupply should maintain power to the chassis for about 250ms ( my memory coucl be off on the time). If the power supply is faulty, either the signal is not sent, or cannot provide power long enough for the CPU to switch.