Okay got it Thanks anyway. Its actually really easy to open the 7BG3. I was able to fix my usb-connector.

But now I have another problem. My device also was kind of bricked. (Only Arnova logo is displaying followed by a reset.)

I managed to install the drivers as the device has been detected but now any version of rocket android does not detect it. Did i forget something?

I installed the drivers with a blank screen. No USB device is detected when the funny android is on the display

Everytime the device is connected this way it is properly detected by windows. (not adb!) but the three versions of rocketandroid 1.4, 1.5 and 1.29 don't recognize the device...

Here are two images i made and what I did to open it

http://www.imagebanana.com/view/o6uga6fj/IMG_20130106_144428.jpg

http://www.imagebanana.com/view/yznlj6r5/IMG_20130106_144447.jpg

1. There are 4 screws hidden behind the tiny rubber elements on the 4 corners of your device. Remove them.

2. Use a small screwdriver to pop the case open. Its working just like any other media device and can easily  be put together again afterwards (If you are carefull when opening it!)

3. Inside a lot of stuff is taped in its place. Carefully remove the tape. 

4. Voilá you're open. At least the powersupply including battery is easily accessible.