Thank you for your efforts. I developed a state chart of my Kobo. Four states
2. On/permanent blue light
3. Flashing red light
4. Flashing blue light
and several combinations of pressing HOME, POWER and PIN reset to change between the states. Does the flashing light indicate that the device/processor is in a "special" mode?
I found several threads and tutorials to unbrick a Kindle Touch. This device is also based on the IMX508. It seems to be quite easy to put the Kindle into an USB bootstrap mode (a IMX508 feature according to the processor reference manual). In this mode one can load a boot image with some software tools provided by Freescale onto the device, start the system and fix the problems.
Unfortunately, I was not able to activate the USB mode on my Kobo in a similar way.
I am wondering whether the Kobo Touch has also such a USB bootstrap mode or alike (booting from SD card), or whether the Kobo engineers disabled these modes after flashing the image to the device.
Maybe one of the Kobo engineers following this forum can give me or the community some hints.