SNES PAL / NTSC mod (NOT 50/60 mod)

Started by Tiido Priimägi, November 14, 2008, 05:07:31 AM

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Tiido Priimägi

I've got a JP Famicom and EU SNES...

All chips are same, but clocks are different (PAL one has 17MHz, NTSC one 21MHz). The clock signal goes directly to the cartslot side PPU chip... I looked for differences in GND and VCC pin configs, but found no differences (maybe I missed something ?) Putting a PAL clock into NTSC machine or the other way results in off standard screen timings... PAL machine has one additional chip near the crystal, which certainly provides clock for the lockout chip, and may have something to do with the current problem...
Mida sa loed ? Nagunii aru ei saa ;)


The problem:

NTSC machine feeds chips 21mhz (NTSC clockx6)
PAL machine *needs* PAL clocx6 but that crystal doesn't exist so they use PALx4 (17mhz) and a prescaller chip to set it as PALx6.
Putting a 17MHZ crystal causes the CPU and video to run on a lower clock causing the problems you mentioned.

I suggest you add an 4mhz clock on the chroma chip,  disconnecting the NTSC one comming from the PPU. Then switch it into pal chroma mode by changing the NT/PAL pin from GND to VCC.

Tiido Priimägi

Thanks for this info !!!

I just want to get PAL video off my Famicom... the Famicom is much much more modding friendly than European model (which has one side of its board covered with some non transparent stuff). I need to locate sufficient crystal now...

I know nothing about SNES as of yet, except figuring an alternate lockout chip disable mod.

EDIT: Is there any info on the RGB encoder chip (BA6592F) available somewhere ? I could not find any datasheets...
Mida sa loed ? Nagunii aru ei saa ;)


there is a reverse engineered schematic from the 1st model of SNES/SFC motherboard out in the wild (the internet)
That should help you a lot when trying to "hack" it.
Again, I'd suggest you to scrap the idea of messing with the main CPU clock and instead try to inject 4.3mhz on the video encoder.

Tiido Priimägi

I have an intention to add the 4.3MHz clock to the encoder chip, but having no datasheet around and no o-scope(to identify the clock signal) won't make it easy... I'll draw a schematic and eventually figure out the signal, unless someone gives me quick pointers...
Mida sa loed ? Nagunii aru ei saa ;)