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

[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/stat ... 65829?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

Update
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.

Here is a video of the noise I experience with a Genesis game running. This does not happen during a 32x game.

https://youtu.be/8-Pkw9sQ1EE

Any suggestions?

[NewSchoolBoxer]

Cool project with real dedication. I haven't tried modding and I don't own a Genesis but I've dealt with electrical noise in MATLAB and Audacity and measured in circuits.

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.

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.

Aluminum conducts electricity almost as well as copper, I'd be using electrical tape here.

64 wires and I saw the wiring pictures, you're going to have serious crosstalk noise and putting the combined Genesis and 32X boards together in close proximity, if that's what you're doing, is going to create noise too. Needing a different power supply for what I assume is more power means the power dissipation is greater as well. Could be worth using a multimeter with temperature reading to see if the chips are within the allowed temperature range. Try a computer fan if you have one sitting around.

I wish I could find the post but there was someone who plugged just the sync line in, not the video, and that created noise on the screen due to noisy sync coupling on the RGB lines. Should try that. Maybe you can compare Composite/S-Video/Component/RGB (not sure of mod details) that use different parts of the circuit board and see if noise is better or worse.

If you have an oscilloscope, you could investigate more thoroughly and see if video line powerfactor needs correction or if CSYNC is lagged too much behind RGB. Look for transient spikes that voltage regulators can help with and possibility of overvolting.

[PeterWar]

Amazing project, congrats!

[Bratwurst]

Are the laminated foil sheets grounded?