I have a PAL GC and i've been using it with the original rca (composite) cable. Till now. I have bought an RGB SCART and... it made the picture and sound worse!
The colors are more vibrant but the screen is fuzzy especially in the light-blue and yellow-orange territories. It's a different fuzzyness to the well known composite and RF fuzz. Oblique lines scrolling from top-right to bottom-left.
The sound is noisy when the image is brighter - a quite loud noise can be heard when the screen is white.
My Dreamcast looks perfect on the same television with RGB scart.
Is it a common problem with some GCs or cables?
Official cable or 3rd party? Check for resistors and capacitors inside the plug.
4€ 3rd party from the local shop - it really could be the problem? Is a branded 3rd party cable would do? i really don't want to buy that 30€ offical nintendo cable if its not neccessary.
The official cable shouldn't be necessary as long as the circuitry in your's is the same. In fact, I don't think I have any official AV cable on any of my consoles!
Will the scart end of the cable open up without damage?
It does and seems it has all the stuff needed.
If it's from a local shop, quickest/easiest way would be to get a replacement. Something seems mis-wired to me.
The store replaced the cable but the result was the same. I started suspect there is something wrong with the GC or the TV.
Then i found a good deal today. An official Nintendo RGB cable, boxed for 10 eur.
I have connected it to the TV with tremulous hands.
Then my jaw has dropped.
The image and the sound is excellent. Even better than the Dreamcast RGB. It is just perfect. I can't imagine what the component cable could add to the quality.