Experiencing "snow" effect on video signal

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Moo
rebel
Posts: 17

Experiencing "snow" effect on video signal

Post#1 » Thu Jun 16, 2022 3:46 pm

I'm running my VA1 via VGA and in the last week it's picked up a serious problem with static-like noise all over the picture. At first I thought it was my television but no other system I tried had this issue, I'm certain it's the console itself after running it through my GBS8200 upscaler and still experiencing this problem.

I've included a video of the issue to YT here:
https://www.youtube.com/watch?v=9Md9W1ED0LU

My immediate instinct is to check for issues around the video DAC area and the components, but I think its worth asking first.

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MondoGecko
minority
Posts: 69

Re: Experiencing "snow" effect on video signal

Post#2 » Thu Jun 16, 2022 9:36 pm

I've had the same effect but it's not the entire screen, only a small portion. It's definitely the same artifacting though. However, I've only seen it happen in Sonic Adventure, and only in certain parts of the game. Sand Hill is bad for it, at first I thought it was meant to be a sand particle effect until I saw it happening on the black screen when the level ends. I then noticed it happening in other specific areas of the game. This happens through VGA and composite. I'll test Dino Crisis tonight. Are you using a GDemu? Is it a clone?

I hope you figure this out because this kind of artifacting has been driving me crazy.

EDIT: Dino Crisis was fine. So far I've only seen this happen in SA.

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Moo
rebel
Posts: 17

Re: Experiencing "snow" effect on video signal

Post#3 » Sat Jul 09, 2022 10:41 am

Here have an update: I had a cursory glance at the signal path the VGA pins take from the AV port back into the system, the only components between the RGB encoder and the output are a set of 75 ohm resistors and a ferrite bead for attenuation and smoothing. I was worried that the RGB encoder chip (SEGA 315-6258) was dying, but after replacing it with a chip from a dead motherboard I'm no worse off than when I started.

I'm beginning to worry that this issue may be coming from somewhere further in the system, if it's in the Holly chip then I doubt there's very much I can do about it.

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Moo
rebel
Posts: 17

Re: Experiencing "snow" effect on video signal

Post#4 » Sun Jul 10, 2022 11:17 am

megavolt suggested that the power supply's interference could be causing it. I was using an aftermarket 12v power supply internally which fed into a Pico-PSU. I swapped it out for an external one I'd used in the past and the video noise is completely gone.

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-drez01-
Tank Jr.
Posts: 344

Re: Experiencing "snow" effect on video signal

Post#5 » Sun Jul 10, 2022 11:46 am

megavolt FTW!

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MondoGecko
minority
Posts: 69

Re: Experiencing "snow" effect on video signal

Post#6 » Mon Jul 11, 2022 5:37 am

Power supply interference makes a lot of sense. I've removed the 12v rail and resistor in mine and I assume that's what could be causing my issue, although it's very strange to me that it's only been happening in one game. I'll have to do some testing with mine. Glad you got your issue sorted!

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