The circuit schematic for my PAL RGB -> S-Video converter is below. You probably want to look at the notes about it too. If you want to print it out then grab the PostScript version or the gschem version.
All Vcc connections are +5v
|C14, C17, C18, C19, C20, C33, C34, C35||100nF|
|C15, C21, C27||10nF|
|C22, C28||47uF Electrolytic|
|C25, C26, C29, C30, C31, C32||220uF Electrolytic|
|R2, R3, R4, R10||1K Pot|
|R7, R8, R9, R36, R37, R38||75 Ohm|
|U1||CXA1645P Video Encoder|
|U2||LM1881N Video Sync Separator|
|U3||74HCT04 Hex Inverter|
|XTL1||4.433619MHz Parallel-Cut Crystal|
The CXA1645P seems to be reasonably difficult to get hold of according to the emails I get about this circuit. I got it from RS Components.