Kevin Horton might have some things to say about this since he's been involved with the RGB and S-Video modes for the 2nd-gen model in the past (yes I know you're talking about the first-gen models):
http://www.gamesx.com/rgbadd/snes2rgb.htmhttp://www.gamesx.com/rgbadd/snes2svid.htmI'll send kevtris a PM point him to this thread so he can maybe shed some light on what you may be seeing.
Thanks!
The only thing I can contribute at this point is a small story:
Back in 1993 when I attended Apple Expo West in San Francisco, after the expo a bunch of us went back to a colleague's house in Berkeley. One of the attendees had hooked up a SNES to an Apple IIGS monitor (which takes RGB in). The picture quality was amazing, but you probably know that by now. But two things caught my eye:
1. What I saw consisted of a customised AV cable that had some capacitors soldered in-line,
I know what you mean. The "scart" cable that has rgb is what is used to get the rgb out. It has some 220uf caps inside it for the dc filtering.
2. Sitting on the chair next to the monitor was a hair dryer.
I asked quite literally "WTF?" with regards to the appliance -- I was told that if the monitor was cold, it wouldn't show jack squat picture-wise when hooked up to the SNES (more specifically: "you'd have to wait quite literally a couple hours for it to get warm enough for it to work"). Using a hair dryer on the monitor (blown into the ventilation areas) apparently sped the process up greatly (to something like 5-10 minutes).
Why the hair dryer was
truly needed I have no idea (from an EE perspective I mean), but I was assured by 2 separate people -- including one quite well-known fellow who worked for Sega writing compilers, as well as some SNES games (for a different company) as well -- that there was in fact legitimacy to it.
The only thing I can think of is the electron gun heaters inside the neck of the CRT tube. It makes the orange glow that you can see in back of the tube. As they heat up, the more electrons they throw off, which can affect the brightness of the picture. When CRT's get dim, usually the heaters are wearing out or get corroded.