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Konami Hornet 24khz Video Noise

JohnRambo'sKnife

JohnRambo'sKnife

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I have an original Gradius IV board that I use the jamma adapter for controls and the VGA connector for utilizing 24khz output. I run this to an OSSC in line double mode to an NEC Accusync 120 CRT.

In 24khz mode, I get a large amount of inteference and minor ghosting. I am using an Extron VGA cable, so quality of cable is not suspect and it has been swapped around. The noise is most visible on the test grid and presents itself as a sort of wavy pattern across the entire screen. I have not had the opportunity to try it in a cab using the jamma adapter to pass the 24khz signal.

I've also tried running it through an Extron 160 interface to see if I could stabilize the inteference. No dice.

I also tried a custom VGA to Scart cable I wired up from a spare Extron VGA cable and even with all the LPF tomfoolery shit turned on and phase adjustment, I could never get it to not show the wave.

Also tried passing it through the XPC-4 but same result. Could this be a bad diode or is my board possessed by Max B?

Any help is appreciated.
 
My first thought was the VGA cable but you addressed that

Maybe theres some kinda grounding interference feed back in your setup somewhere with the power supplies just throwing out ideas?
A quick test might be to run an extension cable from another outlet to your system board and seeing if the interference goes away?? I read and seen some crazy things over my years in IT and just working with stuff worth a shot?
 
nem said:
Have you tried a different PSU to power the game?
Click to expand...
Not yet. I am using a MW 606. I have another I could try but all other boards are fine.
GeekMan1222 said:
My first thought was the VGA cable but you addressed that

Maybe theres some kinda grounding interference feed back in your setup somewhere with the power supplies just throwing out ideas?
A quick test might be to run an extension cable from another outlet to your system board and seeing if the interference goes away?? I read and seen some crazy things over my years in IT and just working with stuff worth a shot?
Click to expand...
I will give that a try.
 
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I also have bad interference when I try to use Line2X but Line3X works perfectly (set H. backporch 34 to fix left side cutoff).
Of course it depends whether your display can receive the Line3X resolution (1600x1173 on my LCD).
Some PCBs for some reason don't work well with Line2X (also had problem with PGM) but higher line scaling modes work OK.
Give it a try if your CRT can sync to high resolution. Or see if passthru works, although I assume you already tried direct VGA and it didn't work.
 
For ghosting, check that video ground is connected to something or tied to GND on your JAMMA harness.
If they're left floating on a long JAMMA harness while you are using only the VGA for display output, you might get ghosting.
 
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