I can't rule out that there were batches that were pre-overclocked, though I have yet to come across ones that weren't modified. Usually you can tell by the solder or difference in resistor packages/markings compared to the other ones on the board.
( Or you can tell because they stuck an
antminer u2 on a giant heat sink with hot glue )
If you can share a picture/information on where you got it, it might be easier to determine
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
That said.. the resistors should only handle some overclocking, and it should be mining - even if only for a little bit until things get too hot. I'd check if it's detected okay first (cgminer/bfgminer/whatever), as it seems more likely to be a software/driver issue. If it isn't, then hopefully that doesn't mean you've got dead miners.
You can continue asking in German, by the way - this is the German subforum after all - and I read German pretty well. Writing, not so much
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)