Genesis 3BP Followup - VA6 Audio and alternate methods

This isn't a full install video, but I had some thoughts (and received a comment) on some aspects of the install. So, I tried a few alternate approaches I wanted to go over, as well as showing what a full audio install looks like.

Parts List (Non-affiliate):

[emmettturner]

As you can see, the ground pad is part of the ground plane that is directly connected to the miniDIN. As long as the miniDIN is soldered to a ground plane on the Genesis board, you’re grounded. I’ve even trimmed the ground pad off on occasion since it gives me more clearance next to the full-sized DIN.

[emmettturner]

8:55 “Maybe someone can give me a comment as to why they think this is always recommended”
Sure! At 8:23 when you said “…the pin isn’t connected in the first place” but, well, it is. The trace for pin 54 runs under the VDP to the digital 5v supply rail. You can see where the digital 5v rail goes under the chip at the top left corner.

The digital 5v on pin 54 is different from the analog 5v on pin 30. Pin 30 has continuity to the output of the voltage regulator that’s closer to the middle on the left edge. Pin 54 has continuity to the output of the voltage regulator that’s closer to the rear of the left edge. SEGA chose to have different supplies for the analog and digital sides of the chip so that switching digital circuits would not cause corresponding voltage sag or noise in the analog output.

This is also what the additional bypass capacitors are for. Both analog and digital 5v supplies for the VDP already have bypass caps on the bottom side but it is presumably not enough since we still see jailbars and other issues. Some argue that the bypass caps don’t help, and they may be right, but it can’t hurt.

On that note, the VRAM is where a lot of the interference comes from and you can see VRAM traces running on BOTH sides of the RGB traces you retained. I did that too on one of my installs but I plan to go back and change it. After all, it seems I’ve retained the very part causing the issue I intended to bypass!

The CSync signal also runs beside VRAM traces, though it is considered digital so it’s less of an issue. Because CSync happens between lines of detail we don’t have to worry about capacitive coupling of CSync into the video when routing a clean CSync line with RGB, but a dirty one with VRAM noise might be a problem.

I keep thinking about how sync on Composite Video (CVBS) causes an audio buzz with unshielded cables, especially on white screens. This is the color information bleeding into audio. I think it would pretty pretty hard to notice noise that bled into CSync subsequently bleeding into the RGB video lines but, hey, if the whole point of the bypass is to isolate from it then I guess it makes sense to keep them isolated. I just might lift and bypass sync too.

[Seathasky]

Thanks for the video! Would of loved to hear how it sounded!

[emmettturner]

I’m not sure if it matters but the ground you chose was on the digital voltage regulator. The reason the Genesis has two regulators is to keep analog power isolated from digital so that noise from digital circuitry doesn’t find its way into video and audio signals from the power going into the analog amps and DACs. It’s all the same ground but perhaps a closer ground point or the other regulator would be better.

That said, you are already grounded through the miniDIN. You can see that the ground plane on the 3BP v2 board extends from that pad to the mounting tabs on the miniDIN. That is why the Model 1 guides leave it out.

[RadioMartyTB]

This makes me feel bad....for getting rid of my Genesis years ago.
Great work as always. Any PS1's or XBOX's in the future?

[GodKitty]

The pins break very easly but the good news is that you can get a new VDP chip. Also you can connect to the way in the video and then remove the resistor on the other side of the board. This allows you to keep the pullup resistors on the PCB but stop the BGB signal from continuing on to the next IC.

The added caps are for filtering the ripple from the 5 volt supply.

[ICExMikey]

Would love to see a vid for discarding the serial port. What other parts can be discarded etc

[ReneOne]

R55 R56 and R57 are pull ups and should do the same like the 3 resistors you soldered on the 3bp board.

[zoeyzhang]

Not sure if any small custom PCBs may help for repairing? If so, would like to sponsor some. (PCBWay zoey)