My problem is partly solved. In fact I did had several problems causing the systems not to boot.
To try whether it's the cable I used an expensive one: Monster Cable USB. And it didn't worked either. But thats because of the second problem: Sometime it does try to boot, sometimes it doesn't. Like discribed here (http://elinux.org/R-Pi_Troubleshooting# ... not_always
) I took out the fingers of the SD port, bend them up and blow the holes. After that it tryed to boot more frequently.
As you described (for the others: http://elinux.org/R-Pi_Troubleshooting# ... r_problems
) I measured the TRs. And as you predicted my cheep ass china cable caused the voltage to drop to 4.5 V. Just the USA Monster Cable preserved the 5 V. After that, when the system tried to boot. It worked.
Now the only problem is that it does try booting just one time of 6 tries. The fingers of the SD port are not the problem, as I do not move the system when taking away the electricity and try again. I checked the F3 Polyfuse (http://elinux.org/R-Pi_Troubleshooting# ... r_problems
) it is fine. So one remaining reason could be the SD cart itself. This problem is discussed here: (http://elinux.org/R-Pi_Troubleshooting# ... on_display
). I now bought 2 expensive Sony SDHC at a local reseller, to prevent it being counterfeit. My now used SD card is one from ebay China for some few $. It was a mistake^^. I will let you guys now how it worked out, as maybe someone will find this post in Google and benefits from it.
Thank you very much Burngate
Yes, an expensive SD Cart solved the Problem
- - USB A to micro B Cable was to cheap
- SD Card was to cheap
Replaced both with units of better quality: Worked