S7-300 cpu lost it's DB contents

Yesterday a customer called me and needed assistance because his machine was not working any more, i discovered that it was not working because the plc had lost the contents in all DB's so they we're reseted to "0".
It was easy to restore the values that it was programed with from the factory (positions etc) but values changed by the customer was lost and nobody knows how it was configured for optimal performance.

I have been using S7-300 cpu's for several years now and i have not had this problem before (atleast no customers had called and informed me about it).

How could this happend and what can i do to make sure it doesn't happend again?
The day before this happend there was a thunderstorm, could it have been caused by a stroke of lightning?

The CPU in this specific machine is a CPU314C-2-dp

Yes, electrical problems may cause the problem you have seen.

What has happened is that during a shutdown, where the CPU writes the actual values to the MMC card, something has caused some of the values to become corrupted. Upon startup, the CPU detects these corrupt values and decide to load the actual values from the initial values. The initial values are typically zero or set to some safe but unrealistic values.

To my opinion this is a serious deficiency with the design of the S7.
S7 and STEP7 lacks a feature to upload the actual values to the offline project, and a feature to set the initial values to the actual values.

Ok then atleast i know how to explain this to the customers when and if it happends again

You can upload the actual values to the offline project by open the DB online and save it, then the values are stored in the offline project.

smf said:

You can upload the actual values to the offline project by open the DB online and save it, then the values are stored in the offline project.

Click to expand...

If the timestamp do not match you will lose all symbols inside the DBs. This is a small catastrophe if it happens.
If for any reason you touch the DBs, a new timestamp is generated. For example, when working with SCL (which I happen to do a lot), when you compile the SCL code all DBs that are addressed in the SCL code are generated anew.

I have only once worked with S7-300 and that was some years ago. I usually work with S7-400 and backup my program and data to a Flash Memory Card. This seems to avoid the problem. Others can comment on its application to S7-300.

Jesper got it covered.