Hi, this sounds like an awesome mod. But I do have some questions:
1) Does the board allow for the behaviour to be turned off with a switch if you don't want it?
I know this might sound like an odd question, because why on earth would you *want* that extra PPU cycle, with all problems it can bring on some displays?
Well, the thing is (and this is probably irrelevant to 99.999% of the people who want to just play games) - Blargg's nmi_sync library allows sync:ing the CPU to the PPU as exactly as possible: 1 pixel jitter on NTSC, and 1.5 pixel jitter on PAL:
http://wiki.nesdev.com/w/index.php/Cons ... ronizationThe long-winded explanation is for PAL only, but the same principle applies in the NTSC case. And I believe the library itself uses the shorter frame to make the remaining jitter on NTSC be just one pixel.
Blargg's library enables new awesome uses of the PPU that I hope will show themselves in homebrew software eventually. I'm not sure what would happen if every frame is the same length, but I presume that the code would basically revert to the PAL case of a slightly bigger jitter of 1-2 pixels. And it'd be a shame to totally lose that "feature" of 1 pixel less jitter on an NTSC NES...
2) And speaking of losing features, I think Tim's NESRGB board is a great mod that I'm happy with overall, but it does have a bug that would be worth fixing if the hardware is being upgraded anyway:
http://forums.nesdev.com/viewtopic.php? ... lit=NESRGBAgain, no commercial games would be affected. But for a homebrewn NES game I'm developing I've coded a pretty neat water effect that spends 2 scanlines to rewrite the entire palette to look more blue. Rewriting the palette requires turning off rendering, and in order to not get the rainbow colour effect I also set the monochrome bit to displays some grays and whites during these writes. The result is a sort-of-believable shimmering water surface of whites'n'grays on a CRT, and on the Hidef NES (which correctly emulates the PPU quirk of displaying the palette colour during palette writes)
But on Tim's NES RGB my water surface shows up as black instead, which is kind of ugly.
If my homebrew game ever gets released, I won't let the NES RGB stand in the way of the nice-looking water, and would just tell NESRGB owners to switch to composite, or just squint and pretend that the water surface looks white.

...but it would be great if this bug could be fixed in a new revision.
3) Last, just a personal question on why my setup behaves weirdly: I have an OSSC and a PAL 1chip SNES modded with the SuperCIC mod. The SNES keeps losing the picture on my HDTV in 60Hz, but is fine in 50Hz. I know the most plausible reason is that shorter scanline, which this mod would fix.
But the odd thing is that my NES (which has Tim's RGB mod) runs at the same 60.08Hz frequency, has the same shorter scanline as the SNES, and should suffer from the same problem. But curiously, it delivers where the SNES fails and never seems to lose picture with my HDTV.
So I am quite surprised that one system works perfectly with my HDTV but not the other. Does anyone have any thoughts on why?