Megadrive 1 RGB Scart issues...

[Simon_G]

Hi guys, long time lurker, first time poster, and yes I have used the "search" function but not came across the problem I seem to be having.

I have made up an RGB scart as per the instructions on a few sites, however I am getting jailbars (is this RF interference?) on the blue channel, although more strangely, the caps I am using (220uF 10V) make no difference to the birghtness of the image. For the record I am also using 75 Ohm / 0.25w resistors as per the instructions too.

I have stripped the cable, and even gone to the extreme of making a setup on veroboard to make sure that nothing is touching, and the resulting output is still the same on whatever TV I use.

Interestingly, when I use the same cable on a Master System, the picture is perfect apart from a load of RF noise.

I have also tried the same setup WITHOUT the caps as per the guide on MMMonkey.co.uk and there is no difference.

I'm out of ideas, so any pointers will be appreciated.

My setup (yes I know there is no audio - I had a twin core audio lead running into the scart, but removed it to remove it from the potential sources of the problem)...

Din Plug Scart Plug

1 Not used
2 4, 17, 21 (ground)
3 20
4 8 (connected to 16 via 180 ohm resistor)
5 75ohm/220uF 11
6 75ohm/220uF 15
7 Not used
8 75ohm/220uF 7

 

[Bibin]

Try an alternate power adapter - it's possible that yours isn't putting out a particularly clean and smooth voltage.

 

[Drakon]

caps won't make a difference on how the image look unless they're on sync. They'll just keep out extra voltage. What're you wiring this into, a scart tv? A scart to component adapter?

By the way all genesis/megadrive systems I've come across have jailbar like interference in the rgb (and s-video when you add that modification). There's also a funky rainbow effect that goes on from the system that doesn't show up on tvs. I'm currently working on a way to clean up the image but it's really complicated. I basically wired a cxa1645 circuit into the system and here's the difference:

 

[Bibin]

Yes, the CXA1645 buffers the unclamped RGB much better than the 1145 does - the Sega Master System has the same jail-bars.