It is a good idea always to have a look at the end of the mains cable automatically, before one puts his fingers into any equipment, to check that it is not plugged into an outlet.
Enough for life saving.
How to connect
The Input signals to the RGB to PAL encoder can be found under the decoder board on the component side of the main board.
RGB can be found at R3710(red), R3713(green) and R3708(blue), at their end closest to the scarts. The composite sync can be found at R3022 (2k2) at the end closest to the connector for the Decoder board.
A 12V connection must be taken as a supply. There is also a 12.5V supply point on the board, DO NOT TAKE THIS ONE!
I took the Ground from electrolytic capacitor 2872 (negative side, of course, nearest to the scarts) and the 12V from a bridge nearby. (I cannot read the label any more, it seems to be 9834.)
Take care not to bend the connector to the Decoder when taking the Decoder off or reassembling it. Read and follow the short text under the diagram! I killed 2 MC1377's by being careless with input signals!
Use a socket for the MC1377 and leave it empty while soldering your circuit (but don't forget to put it in afterwards!)
So, I hope this is of use for anyone and there are no people out there who had a business doing exactly what I describe. Anyway only persons with a little experience will be able to do this.