STEP7 Hardware problem??

[Greet]

Over a period of 6 months I had to change two output-cards.
I'v changed them because the card has some outputs that were broken:for example:
Q2.5 was always on, and after a period Q2.6 is also on , but not in the software!!!
The last time I had to change an inputcard also: an inputsignal was on in the software, but not in the hardware (24V over the contact of the card !!).
We have measured the whole system, and everything looks OK. This installation is already in production for about three years: we never had some problems, except for the last 6 months.

It's an CPU318-2DP and the outputcard are 322-1BL00-0AA

Does anyone know a solution?

 

[Gambrinus]

Over a period of 6 months I had to change two output-cards.

IMHO, everything only looks OK. 2 modules in a 6 months is too much. What loading is connected to this outputs?

The last time I had to change an inputcard also: an inputsignal was on in the software, but not in the hardware (24V over the contact of the card !!).

Hm, it looks strangely. 24V presents on input, you don't see LED but see 1 in a program? As I know front LED of input is connected in serial with internal LED of optoelectronic couple. Usually LED is on but in PLC memory this bit is off for defective input.

 

[Greet]

The loading of the outputs:
- first change of outputcard: the outputs that failed were relays
- second change of outputcard: the outputs were just control-leds !!

Problem with the inputs: no led on the input-card, but in software(online, the input is on !!

 

[Gambrinus]

I don't know what just causes your problems. Siemens' equipment reliability is good. But not 100%. Module can dead. But "This installation is already in production for about three years: we never had some problems, except for the last 6 months."
is fishily. Bad module dies faster. Furthermore, died only external part of input or output, not internal. It seems problems with powering and grounding, IMHO.

 

[JesperMP]

When I have had S7 modules go bad, upon inspection of the defective modules, there were always electronic components that have gone visibly bad (burned).
Like gambrinus asked "What loading is connected to this outputs? ".