Hey, I'm new to these forums, and a little new to modding in general, and aware this thread is old, but (to me) it is the most logical place to put this post.
In relation to the NES 50/60Hz mod (also noting this thread and associated info: http://nfggames.com/forum2/index.php?topic=4226.0
) I am picking up where Phreak97 left off.
theres gotta be a way to do it though, even if it means jamming most of the guts of two consoles into one casing. could you install two sets of cpu, ppu, and clock, then have a switch to choose which ones to use?
I have a PAL NES, and the following info:
PAL NES runs a 26.601712MHz crystal with the 2A07 CPU (2C07 PPU) using a 16x divider (1.66MHz CPU speed)
NTSC NES runs a 21.47727MHz crystal with the 2A03 CPU (2C02 PPU) using a 12x divider (1.79MHz CPU speed)
The PAL/NTSC CPU's have DIFFERENT audio hardware in them, therefore, if the CPU ran at the correct speed, the sound would be wrong.
This results in the requirement to have BOTH CPUs installed. I have piggybacked the CPUs together, leaving /RESET selectable (one CPU running at a time).
Running the NES this way, i have found the following combos of CPU/PPU/XTAL to do the following:
2A07/2C07/26MHz: this results in normal PAL functionality/video/sound.
2A07/2C07/21MHz: this results in slower than normal sound (and video). The system is responsive, but slower, and the video is no longer syncable on a PAL/NTSC TV.
2A03/2C07/26MHz: this results in a no-go situation. No sound, no operation, but a stable, synced white screen.
2A03/2C07/21MHz: this results in a no-go situation. Maybe 1-in-100 power-cycles the system runs with no syncable video, and sound of unknown speed (haven't been able to time it properly to find out).
Looking at the schematic http://www.freeinfosociety.com/electronics/schemview.php?id=2405
the power/reset/LED connector section/pinout is incorrect. This will be important to know if messing with the CIC for an auto-switch version of this.
Alongside that, it isn't exactly clear to me as to how the oscillator for the NES works; there are like 3-5 clock inputs to the PPU, alongside the lock in/out of the CPU. MAYBE a dual-oscillator could be used to run the PPU at a different speed (to the rest of the system) to get in sync with the CPU (reason the 2A03/2C07 don't like to talk to each other?), but in doing that, it's video-out (colourburst, etc) will
be all screwed up.
So, the above testing/info shows that... the addition of an NTSC PPU (2C02/2C03) will likely result in a dual-region system.
I'd love to test this theory, but i have no cheap/easy source for the 2C02/2C03. (I can't justify the cost of an entire playchoice PCB hoping that the PPU is PRESENT, let alone if it will work in the PAL NES.)
As soon as i get my hands on a 2C02/2C03 (if anyone has a spare lying around, PLEASE PM me), i'll have a go at combining it all, and adding support for auto-switch, like Phreak97 has done with the SNES (using the CIC against itself) http://nfggames.com/forum2/index.php?topic=3057.0