There are only two pal motherboard revisions, I thought both done S-video, but just have missing components and need a modified cable that has them added back into it. Like what
http://www.consolegoods.co.uk sell.
Far as I know, first revision (NUS-CPU(P)-01) will work without added components, but picture will not look right. Second revision (NUS-CPU(P)-02) will display nothing without the modded cable.
Anyway, if you must change, I would just ask for the serial, rather than asking if it does S-video. That is how I grabbed my RGB moddable NTSC machine (checking serials). Much easier than asking for technical details, from people who may not know.
According to this list from here
http://forums.modretro.com/viewtopic.php?f=33&t=1417
European
NUP13723487 - NUS-CPU(P)-01
NUP13892869 - NUS-CPU(P)-01
NUP15465864 - NUS-CPU(P)-01
NUP15754441 - NUS-CPU(P)-02
NUP15787038 - NUS-CPU(P)-02
NUP16551203 - NUS-CPU(P)-01 (Pikachu Model)
Anything under 154XXXXX should be the first revision board. If you can't get S-video out of one of them, then something else is wrong, as there are only two boards.