Unfortunately, without a modification, the 3DO only outputs 480i and does not output RGB. It does output S-Video though and good mods are available for certain models.
Info / Mods:
3DO’s that use a specific chip (the VT chip) can be modded both for RGB and 240p! 3DO’s that use the “Bt9101” chip can be modded for RGB, but will still only output 480i. There is one motherboard / chip revision of the 3DO that can’t be modded for either. For more information on 480i and 240p, please see the 240p page.
Mod your 3DO for 240p output
Otakus-store RGB kit (for compatible models):
SPDIF / TOSLINK Mod (only certain models).
RGB Mod Technical Info & Service Manuals:
Taijigamer2 emailed me the service manuals for the FZ-1 and the FZ-10!!!
Original RGB Mod:
Here’s a diagram of the actual RGB mod, in case you’d like to try and make your own circuit (experts-only!):. As an FYI, I believe this was the first person to accomplish a 3DO RGB mod: http://www.digitpress.com/forum/showthread.php?81651-3do-rgb-mod-done-and-working!-pictures-included!&highlight=acem77
If you’d like digital audio output, you can try this mod: https://assemblergames.com/threads/3do-fz-10-toslink.58126/
I’d only recommend doing the RGB mod if the 3DO is one of your favorite systems, or if you prefer to run all your consoles through an RGB SCART switch. It’s my opinion that it may be a lot of trouble for a console that doesn’t have a large library and natively supports S-Video output.
That being said, if your 3DO has a compatible chip, I’d definitely recommend doing the 240p mod; It’s not very hard, makes a huge difference in picture quality and works on all outputs (RGB, S-Video, Composite…and even RF).