Built a Sega Neptune in my model 2 VA4. Major video noise now. Please read.

[infidelity]

Hello everyone. Took me 3 days but I did it!
Please check my Twitter link for the video and all the pics from start to finish.

https://twitter.com/infidelity_nes/s...101965829?s=19

So here is the background of each system, want to get that info out of the way before addressing my issue.

The Genesis I have is a model 2 VA4. It has been recapped, has its r,g,b,csync,subcarrier pins lifted from the vdp, r,g,b,csync pins are going through a triple bypass board. This system looked and played crystal clear with all these modifications.

The 32x is a VA0. It has been recapped, and includes the kevtris video fix. When attached to my model 2 VA4 the picture quality was incredible.

The power supply I'm using is a Triad (I think that's how its spelt) and it has the correct voltage.

I'm using an ossc with the latest firmware as of Dec 2020, using custom optimal timings, using a packapunch scart cable.

This Genesis is setup for RGB SCART output only.

With all of this that I've done, the picture quality is phenomenal.

And now, onto the Neptune mod.

On the 32x I removed both AV in/out dins.

From the Genesis triple bypass board, I have the outgoing lines soldered directly to the 32x AV in solder pads on the mobo where the din used to sit.

From the 32x, I have the outgoing lines soldered from the 32x AV out solder pads, going to the 9 pin din now located upside down on my Genesis mobo.

From the Genesis, I have 20 awg pos/neg wires bringing power to the 32x.

The 64 data lines I have, are 24 awg wires that are roughly 3 1/2 inches, to 3 3/4 inches in length.

I have 3 pieces of aluminum foil wrapped in packaging tape, (the foil has 4 layers each) and I have them placed under 1 set of 32 wires, in between the 64 wires, and on top of the other 32 wires.

RESULTS

After 3 days of work, I fired it up last night and everything booted! Genesis games play and sound correctly. 32x games play and sound correctly.

Buuuut, ugh, I've got awful video noise. It's extremely noticeable on a black or dark color background. It gets really bad when the system is activating instructions, like when the system is processing a selection, transition from one thing to another. I even get video noise anytime I initiate my D-Pad to cycle through my Mega Everdrive X7.

I dont know exactly what to look for to troubleshoot this, in fears I'll ruin 3 days work. This was ALOT of labor, I love that I accomplished this, but knowing what my VA4 looked like before this mod, it crushes me. I hope there are people here that can possibly shed some light on this. I came fully prepared to accept video noise after doing this mod, since I'm extending 64 lines of data to roughly 3 1/2 inches. But the amount I'm seeing, and the fact my controller even contributes to additional noise, frustrates me.

Thank you for reading, and thank you for any assistance!

-infidelity

[Phantar]

Hey, first of all: kudos for the job! I have great respect for everyone attempting such a project.

I'm more of a theorist myself, but reading your description I have two questions:

A) what video connection do you use - plain RF, or RGB (or, if you're from Euroland, SCART?) Have you checked whether the issue arises regardless of the video connection used? Maybe it only occurs on one end?

B) Have you made sure the shielding is correctly in place, especially the ones on the video connectors? From what I've heard, this might be a major point of concern?

Oh, and did you follow any specific instructions? I'm not sure what is currently circulating around the interwebs, but I always felt this guide was pretty solid.

[infidelity]

Thank you for the kudos! :-)

This Genesis is setup for RGB output only. I'm using an rgb scart cable (packapunch). Before I did the mod, with only the subcarrier pin lifted from the vdp, the Genesis output an incredible clean crisp picture! Even with my recapped 32x attached, still got a glorious video signal!

As for the shielding, I'm using one of the original metal shielding housings from one of the 9 pin dins. I cut the top of the shielding so that I can place the din upside down. The 4 legs of the metal shielding are placed through the Genesis motherboard, and are soldered heavily in place.

On top of the dins pins i have a db electronics board that rests ontop of the upside down din, allowing me to solder to see pads, instead of directly onto the din pins. I believe I have that board grounded, cause the thick metal leg that comes put of the din, is going through the db electronics board, and I have that soldered, there is however a pad called OV on the board that i do not have soldered, but I figured since I have the metal leg of the din soldered to my board, 2 additional solder grounds are connected to the shielding, and the shielding is soldered to the Genesis motherboard, gave me the impression that I grounded that din correctly.

What would you suggest?

EDIT

Here is the exact board I'm using ontop of my din for the AV out signals.

https://oshpark.com/shared_projects/37rGIZ8P

And I was just informed that OV on that small board, IS ground. So tonight I'll get that fixed and will report back. Crossing fingers that's all it is.

[Phantar]

Like I said I'm more of a theorist than an actual tinkerer, but yes, seems like a lack of proper grounding might be the issue. I wish you all the best.

[infidelity]

Well i got the noise almost figured out. I used a different power supply and it cleared up a TON of the video noise i was having. I still get noise when I make selections with my controller on my Mega Everdrive. It's funny, certain games will have horrific noise in the background, others not. This is most noticeable when I play the 32x Star Wars Arcade, the intro before the logo is clear. Certain Genesis games with a black background you can clearly see video noise.

I also made the proper groundings.

So that's where I am now with my video noise. Any ideas to my new issue?

[infidelity]

I'm posting a link to my video I took, it's my Sega Neptune displayijg video noise only during a Genesis game. When playing a 32x game I have no video noise.

I've cleaned up most of the noise by using an OEM power supply. I also have a Triad power supply. Both give the same results on screen, so I'm sticking with my OEM.

Now, I'm using a triple bypass board for the model 2 Genesis. I had zero noise with this board installed, before I did my Neptune mod. The bypass board is receiving its 5v from the 7805 regulator.

https://youtu.be/8-Pkw9sQ1EE

[Phantar]

I'm afraid I'm out of suggestions. It could be that there is still some sort of power supply/bleed issue when it comes to the Genesis side of things, but don't see where exactly the issue may lie.

/edit: Maybe you're asking in the wrong subforum; Someone checking the Tech-Aid section here at Sega-16 might be more capable to help you.

[infidelity]

Thanks, i made a thread in the tech page leading to here.

So this is my current video noise that I get only when Genesis games are running.

https://youtu.be/8-Pkw9sQ1EE

Any ideas everyone?

[xelement5x]

So to confirm you did already run the 32X through the Genesis with the triple bypass installed right? I'd wonder if it could be the triple bypass causing issues.

[infidelity]

Update: I built a 2nd model. This time I installed the 3BP v2 to the 32x AV in, then the r,g,b lines from the vdp, I intercept before they reach their resistors bu the Sony encoder, I hijack those lines (csync as well) and direct them to the 3BP v2 that is attached to the 32x AV in. I have crystal clear picture now. 😃

[xelement5x]

Update: I built a 2nd model. This time I installed the 3BP v2 to the 32x AV in, then the r,g,b lines from the vdp, I intercept before they reach their resistors bu the Sony encoder, I hijack those lines (csync as well) and direct them to the 3BP v2 that is attached to the 32x AV in. I have crystal clear picture now. 😃

Great news! Sounds like some modifications (or addendums) to the Longhorn tutorial might be needed.