Dreamcast VGA via SCART

[lakeofblood]

Please treat me gently I'm a total newbie as regards these matters.

For various very good reasons I want too use my PAL Dreamcast with my JVC HV-32P37 CRT TV's Component Y Pb Pr inputs. The obvious route to do this is via DC VGA box and a VGA to Component transcoder. Unfortunately cost is also an issue and the solution I settled on was a cheaper RGB SCART to YUV transcoder. 480i/60 or 576i/50 only, no prog scan of course but apart from what I think is called a bit of red push which I corrected satisfactorily by modifying the cable with a resistor I've been very pleased with the PQ.

However now I've come here and found that it is possible to make a DC VGA box to SCART adapter which with the transcoder could give me the 480p option too.

I understand the problem is that a sync combiner is needed to convert the VGA's H & V sync to composite sync for the RGB SCART input. What I just don't understand is the circuit diagram provided here.

In the main circuit diagram, which includes the VGA box, the VGA H & V sync from that are shown going into a 'sync combiner' along with a 5v power conmnection.  

However in the expanded sync combiner circuit diagram those same VGA H and V sync inputs shown going into the EX-OR 74LS86 logic gate appear to be marked as 10 and 9. There is also a figure 8 marked to the right of gate.

I'm sure I'm misunderstanding something so can somebody please explain?

Secondly; the sync combiner circuit designer later seems to suggest that an even simpler solution is possible just by connecting the H & V sync wires together from a DC VGA box, grounded with a resistor. What value isn't stated but if this is a viable solution it would suit my soldering skills far better than having to build a more elaborate circuit. But does it work? Has anyone tried this method and if so what resistor value proved suitable?

Thanks for any help or advice.
 

 
Edit 1: the circuit I'm refering to can be found at:-

http://gamesx.com/wiki/doku.php?id=av:dreamcast_480i-480p_scart_cable


I realise now that the 10, 9, 8 numbers refer to the inputs/output terminals of the 74LS86 logic gate and presumably those are only used because the other inputs/output terminals are used in the DC VGA Box circuit this sync combiner circuit is derived from. That's what confused me.

BTW is it possible to substitute a 74HC86 logic gate for the 74LS86?


Edit 2: I actually found the answer myself: a CMOS 74HC86 is NOT substitutable for a TTL 74LS86 because it has different voltage requirements. But a CMOS 74HCT86 is apparently designed specifically to be interchangeable.