fernan1234 wrote:
A few people were discussing this issue in the new N8 PRO's announcement topic at KRIKzz's forums. This bit of information was particularly important posted by users nuu and Link83 respectively:
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It sounds like this is about CPU-PPU clock alignment. There are 4 possible alignments every Famicom and NES could end up with at each boot. If you have a PPU that has this bug and speckles appears in a game you need to boot it into another alignment that works with that game by power cycling it until it works.
Soft reset will not work (not sure if any games even have this). Hard reset might work on a front-loading NES. For a Famicom and a top-loading NES you might need to power cycle since the reset button doesn't reset the PPU on those.
And
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It sounds like technically the bug is in the PPU, so its not really a fault of the NESRGB or the EverDrive N8. The NESRGB could probably select a specific clock alignment/phase from the four available, but apparently different games respond better to different alignments, and some games cant be fixed at all, so I dont think locking the NESRGB into one specific alignment would really help. Its likely easier to just power the system on/off until you get the desired clock alignment (The reset button will also work on some some systems, but not all of them since Nintendo changed the reset circuitry between revisions and some models dont reset both the CPU and PPU when using the reset button)
I think the only solution really is to either get a console with a Rev.H PPU (Later models of AV Famicom, and perhaps later NES toploaders as well) which apparently fixed the issue, or patch each game to disable writes to the PPU_CTRL $2000 register:-
What I find interesting is that I think this PPU clock alignment bug seems to also affect the stock Composite video output as well:-
A total solution would need to be implemented on a future revision of the NESRGB to avoid this CPU-PPU alignment issue. There may be software/patch solutions but there may be issues with that too. Apparently certain board revisions will not have this problem, but what are IMO the best consoles (OG Famicom and NES consoles) don't have those.
I had a chance to test this out. I had 2 NES Top Loaders; one had the pixel noise issue and the other did not.
The console on the left with a revision H PPU had the issue and the other console had a revision G PPU. According to your post I assumed the issue was the PPU revision. I swapped PPU's and the console on the left still had the issue despite now having a revision G PPU. The console on the right did not have the issue despite now having a revision H PPU. I then tried swapping OEM NES power supplies between the two and that made no difference. I also tried swapping the entire NESRGB kit and that made no difference either. I did many power cycles with each test.
Both consoles were recapped, new L78S05CV's, and Q1 transistor removed. I emailed viletim about this but he stopped replying after a few exchanges. I wasn't able to figure out what the issue is but my best guess is it's the sockets. I could have tested this by removing the sockets but it's too much work to disassemble a NESRGB kit once it's already been assembled.