Honest Bob, you are a great man - I've been hunting for a schematic for years, and then find one within 24 hours of joining this board! I'm gobsmacked, and very grateful! I owe you one! Call the favour in any time.
Power light on, but does sometimes remain off for 2-3 seconds after flipping on the switch - quite odd, some weird capacitor or inductor issue, hmmm.
Nothing on RF.
Audio is perfect, can hear the little Safari Hunter's car chugging along, and responding to keystrokes.
Yeah, I was expecting +5v from the regulator too, weird. Must be too much load. The 2 smaller chips on there can take a wide range of supply voltages, so not sure what they should actually be, might not be 5v. Anyone care to check how many volts on top-right pin of either IC101 or IC102? Can use heatsink on main board for ground. I might have to hook up an external supply after finding & disconnecting the bad bits, see if I can breathe some life into this thing.
Have looked at Enri's stuff cheers, nothing there for me. Also, I think the LM1889 can do NTSC, but I admit I've never seen a schematic, so unsure if that happens on the Sega at all, or if different circuit.
That schematic you supplied confirms what I thought - that T101 is used in some sort of DC-DC converter. I still don't understand why - it seems the sole purpose of that part of the circuit is to generate a supply voltage for the chips - why not just use a regular linear regulator? Perhaps efficiency? Isolation? I shall keep digging. My wife is really pleased at the pile of old electronics that is piling up - I need to fix something soon and reduce that pile!
My other option is RGB! I've also got a Sega Yeno variant, it has a totally different video daughterboard (no ICs apart from a buck-boost regulator, which replaces the T101 stuff I guess), different connector and pin-count, but provides RGB analogue output (with 'composite sync'), but no actual composite output, and no RF. The video chip and/or RAM is stuffed on that Yeno, wrong characters appear on screen etc, but I could use the daughterboard to generate RGB on my NZ model SC-3000H. FYI that stuffed Yeno seller is in denial, watch out for him. His responses to other unhappy buyers have been downright rude. http://myworld.ebay.es/stalvs?ssPageName=ADME:L:OC:US:1181
SC-3000H, SC-3000H, Amiga 500. Hobbyist electronics and programming.