Jailbars when Irem M72 connected to Sega New Net City Cab

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Hello,

I have bought recently Irem M72 Legend of Hero Tonma PCB.

I tried it on 2 setups :

- HAS supergun with meanwell psu gscartsw and a PVM 20L4 : no noise at all
- Sega New Net City + Toshiba PD1843 Trisync Chassis + Riverservice JVS>JAMMA adapter pcb model + Stepdown converter : I get some strange video noise with jailbars. I also have tried the Riverservice harness, tried alternative psus... no difference at all.

I have dozen of other PCBS and I have no video problems with both setups, except this game.

These rainbowish jailbars tend to be attenuated when I adjust horizontal size + horizontal position, they get wider when image is wider, and tend to spread on the image, but still present.

I suspect some filtering unsuccessful, but I have no knowledge on where to look.

I tried to hook the pcb to the HAS supergun + meanwell psu like on the PVM setup, then hooked it to a Scart>Jamma converter, noise is still present, but more attenuated. I am pretty sure something can be done to the video signal to attenuate these jailbars but I still don't get it as it requires knowledge on analog video.

It looks like some video noise on the Sega Megadrive, like some rainbow colored bars I get on some games with the pvm that tend to disappear when image is stretched a bit. But this is on the entire screen especially noticeable on solid colored backgrounds.

I wonder if some device can be hooked between the Riverservice JVS>JAMMA adapter and the monitor to filter video and get rid of that annoying noise. Monitor has a standard VGA input.
Agai'n my guess is some filtering is needed but it's just an intuition not based on real science.

I would be grateful if someone can give me some hint to get rid of these jailbars.

Thanks

 

[nem]

I'm seeing a moiré effect on the screen? Is that it? If it is, it could be a combination of a specific resolution and sync and the actual tube. You could try playing around with the focus pots on the back of the flyback. It could get rid of it, however, the resulting image might be slightly softer. Swings and roundabouts.

Jailbars are symmetrical vertical lines on the whole screen. They don't bend at any point. That's something that is coming from the PCB. You could try searching jailbar fixes for console hardware and see if any could be adapted to a M72.

 

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actually I don't know if we can call this jailbar, it's not perfectly parallel lines like we can see on the Megadrive or the PCE, it looks larger and gradient, like a darker tint overlay, when I stretch the screen they tend to get larger and larger, and they kinda get diagonal to the point they disappear when it's completely stretched, but the image resulting is too big, don't know how to name this problem for sure

 

[nem]

It's moiré.

I had a pretty badly configured Nanao MS9 with a Hitachi tube. I put up a crosshatch screen and adjusted both the yoke rings and the focus pot on the flyback. I got it absolutely pin sharp, with perfect convergence in the center. Booted up the game (Virtua Fighter 3), and it looks amazing -- except on uniform, bright backgrounds when the screen has a very visible moiré effect. It looks exactly the same as the pic in your post.

Oh well.

 

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Sounds like a neverending but attenuable problem, because I've tried 3 chassis as they have different focus/screen settings, it was always there.

I will try to find some time and fiddle a bit on this while the game is playing.

Have you reached pleasant results with this workaround ? I mean is the tradeoff between less sharpness and less moiré worth it to your eyes ?

 

[nem]

Yeah, I left it as is. In my eyes the trade off was worth it.

 

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I've read today some articles about moiré, you nailed it sir ! what is odd is the same resolution coming from groovymame doesn't bother the monitor