OK, I have an English One For All remote here (URC-7550) and it has 8 device codes for Grundig, but none of them are in the URC-7800.

However, two of them have the same format as the Philips TV code 0054, so give that a try, you might get lucky. Try all the buttons and if you can get any reaction from any button, then you can probably fix the rest with advance codes, but if not, it means that your TV probably uses the European signal and that can't be created in the C7.

Rob.