SamyGO

Thank you very much. I've downloaded it and looked into the archive. I've found u-boot.bin and Image in the image folder, but there is onw.bin instead of fnw.bin. Is it ok? What is this image good for? The kernel from arris69 contained only the Image file.

There is one more thing i still don't understand. As you wrote, you only added those three files into the archive. The rest of archive is exactly same as the original archive, so how it's done they get loaded and flashed? Is there any naming convention mechanism which take care of that?

Flashing this FW will fix the u-boot issue as well as enable network support on my TV, right? I'm afraid of bricking my TV so i wanted to try the modified kernel via the usb external boot first, but i'll give it a try in the evening.

it is my typo, onw.bin is right file name
Yes, if you flash this firmware, you will get u-boot for emergency and for external boot,
latest kernel with network support from arris69 (09.12.2010) and full onw partition (tbml4) for properly u-boot work with NAND.
All other files are from original T-CHL5DEUC-2008 firmware, it needed to perform full upgrade with images i added to /T-CHL5DEUC/image folder. If you want, you can flash 2003 firmware back, but u-boot ad kernel remains from this firmware "set"
Yes, flashing can brick your tv, but with cable and working u-boot/TDM (top debug menu) you can always easily restore it. Do not forget check watchdog-off and rs232 to debug.

p.s. if you want, i have patched T-CHL5DEUC-2008 firmware with arfix v2 hardcoded (Norwegian language is gone).
So, here is patched 2008 firmware with same u-boot, kernel and onw images + arfix_v2 (added more screen formats in mediaplayer)+samygo.sh at startup. You can flash this firmware instead first, original i gave above.

I compared this new FW with the previous one and discovered that it doesn't contain the onw image. Can i simply copy the image file from the previous version to the new archive? Will it work?

Yes, you need

Ok. Once again, thank you very much, juuso. I really appreciate your help!

it should work on B6000 too.

You need reflash your u-boot with normal one, because on your TV u-boot is restricted. I do not understand what instructions are you commenting. If you make thesesteps, please, talk about in this topic.
You can`t get to u-boot in step2. You need step2 to make fake upgrade to samsung. Try access u-boot and TOP debug menu just in step3 after you re-flash u-boot, onw. and Image. Read instructions careful.