How would you design a new drop-in replacement Sega Genesis Model 1 motherboard

[seastalker]

So I recently heard Bob at RetroRGB mention how much he would love a new drop in replacement motherboard for an original Sega Genesis...

 

I have a Commodore 64 MK2 board, and admire the Ultimate 64 one and the Atari 800 XL in a 1050 disk drive, Eclair, etc. I really like Bob's idea though. So, though I don't have the experience level to design such a board, I thought about what features would make a redesign worthwhile, and maybe some here would like to hypothesize or render designs of a definitive Sega Genesis/MegaDrive. "If you build it, it will come" type of idea.

 

- With the Analogue SG already out there, I wouldn't go the FPGA route of an Ultimate 64 equivalent as top priority and would favor a MK2 Reloaded type of design, with all specialty chips required easily dropped into ZIF sockets.

- Original stereo headphone/audio jack should remain, but stereo audio should also be available on the rear output. Maybe a triple-bypass built into the design. 

- I always thought the system had built in S-Video and that I had a cable to do so. In this reality now my upgrade back in the day was perhaps a composite AV cable instead of RF. I guess the magazine EGM didn't showcase a S-Video upgrade after all and instead when I was presented with the sharper video detail comparison of the 'Don't Walk' sign in Batman, it was for the upgrade to a composite AV cable only... so strange! Yet, I'd hope for a S-video out port common replacement of the RF which would fit the plastic shell's hole. 

- HDMI, even if micro with adapter would probably fit the channel-select plastic hole. 

- Probably a good switch is to make a custom AV port which would match the Model 2 Genesis AV out but with extra plastic to fill in the space of the shell's hole. The middle-man of cable adapters could be avoided in this way and cables could be compatible with other Genesis models and even the TurboGrafx-16

- Was the "EXT" port ever even used??? Maybe that is better for a full size HDMI out port? SD card for rom loading? That would require adding supporting features to the board, I know.

- Clean power supplies already exist like the TRIO and DUO, so the power port likely would remain unchanged.

 

With the above, I can see at least a jailbar-free clean audio/video and power new Genesis.  Now, I'd love the experts to chime in:

 

1. What original specialty IC chips are still in production if at all?

2. I'd assume the Yamaha sound chip is a must have, but could/should any ICs be integrated onto the board (like the PLA on the Commodore 64 Reloaded board after a claimed 100% reverse engineering by Individual Computers)?

3. Where would subjective outcry start to dominate the feeling it is no longer true to the vision of a board? Think of an army of RAM chips on an original C64 get consolidated onto a C64C and really optimized and consolidated on the Reloaded line?

4. What capacitors, resistors and other components could be reduced in trace requirements with modern technology to make both a cleaner board and energy efficient to use a standard cell phone charger for power?

5. This will be divisive I'm sure - purists will want the expansion port for a real Sega CD and physical copy of games. Those with burned only copies and or a Mega SD wouldn't need it. Should it be removed to save costs or used to support USB controllers for example?

 

Finally, I suppose all in the ideal world would unrealistically want a Mega SD FPGA built-in to the board regardless of Terraonion's closed source proprietary work extremely unlikely. 32x support as well to be that prototype Neptune or Pluto all in one Sega system.  I would LOVE to see that someday but more immediately, I do think the Sega Genesis deserves a drop-in replacement motherboard as per Bob's off the cuff aside.

 

I hope others here will comment, create pictures, or more here, even if the fruit of the labor is merely hypothetical. I love this kind of stuff!

[derFunkenstein]

I think the only way to do it today is with a GOAC (which can probably do better than the crap from Hyperkin/GamerzTek/Retro-Bit which normally use them) and then set up an RGB and audio chain similar to that of db Electronics' Triple Bypass boards (which itself is based on existing tech and Ace's Mega Amp). The only other solution is cannibalizing boards, and that leads to very expensive boutique stuff like the original Analogue Nt or their consolized MVS. 

 

The EXT port is required for some outboard development hardware, like GEMS. I don't see a reason for it on a new console. 

Edited September 29, 2019 by derFunkenstein

[seastalker]

I haven't kept track of which original retro ICs are still in production or not, and I suppose getting spare chips off older Sega boards would require much more skill than popping out socketed Atari ones. Tectoy in Brazil, if not for import/export issues, would be an interesting company to consult with about ICs or GOAC. I don't know the current status of production GOACs, but it seems unlikely and unnecessary to create a GOAC from an open-source FPGA core. Probably the best we will see is more like the Ultimate 64, with or without sockets for real Yamaha chips. Not that that's a bad thing. That or a project fitting a Mister or Analogue SG (or future FPGA product) in a G1 case with a DAC.