Hey guys, I just finished looking inside my broken Japanese Saturn and here's what I found with respect to the power supply. N.b. while I'm technically an electrical engineer, I work as a programmer and haven't done any real hardware work since my senior project outside of breaking retro game consoles.
Anyway, a general description of the circuit can be described as follows:
Vin->transformer->fuse->voltage regulator->power delivery circuitry.
The voltage regulator is labeled as a C5215. I couldn't find any documentation on that specific chip but 5215 seems to be common as a surface mount chip nowadays. Looking at digikey, the 5V version operates well up to 13.2V input. Assuming Sega used a 100:9 transformer, a 120Vac input would output a 10.8Vac which is well below the rated voltage of the regulator. Regardless, there is also a fuse in the way so I doubt there's really much risk of damaging the regulator or any of the circuitry beyond it. If you're going to break anything it will be the fuse and that's incredibly simple to fix.
That said, there's probably a lot of systems out there that weren't designed to that tolerance, especially systems with more limited runs that weren't intended for use outside of Japan. I'm guessing Sega designed the Saturn's power supply so that it would work in both Japan and the US. Why waste engineering resources on multiple power supplies if you don't have to?
I still don't know why my Saturn doesn't work though which is a bummer. I get absolutely no life out of it. I can tell you that it isn't because I plugged it into the wall in America though. I got no response the moment I plugged it in from Japan. If it was an issue with US power, there would have been a light flash or something before it died. Also, my fuse is perfectly intact and none of the circuitry in the power supply shows any visible signs of damage. I guess without hooking it up to a DMM I won't know for sure if there's any power but it's past midnight so that'll have to wait until another day.
