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Thread: RGB MVS noise / interference

  1. #1
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    RGB MVS noise / interference

    Hi friends, i have some noise / interference on my video output RGB of my MV1C.

    like this:



    i use din8 megadrive 1 SCART RGB standar-cheap cable without shielding ( that can be the problem ? )

    Have pot resistor 1k on lines RGB / 5k CSync and 220uf caps on RGB.



    How can i solve? thanks!
    Last edited by Jonap; 10-25-2020 at 05:17 PM.

  2. #2
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    ChuChu Flamingo's Avatar
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    A cheap cable can easily cause a interference pattern on the screen that looks like a ~ or a diagonal / wave effect. Especially if you're using composite video as sync and not composite sync (sometimes referred to as pure sync, CSYNC, and many others) / luma sync on a unshielded cable.


    but yeah you need to state what type of supergun you are using + monitor/setup.
    Last edited by ChuChu Flamingo; 10-25-2020 at 05:26 PM.
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    Quote Originally Posted by ChuChu Flamingo View Post
    A cheap cable can easily cause a interference pattern on the screen that looks like a ~ or a diagonal / wave effect. Especially if you're using composite video as sync and not composite sync (sometimes referred to as pure sync, CSYNC, and many others) / luma sync on a unshielded cable.


    but yeah you need to state what type of supergun you are using + monitor/setup.
    Thanks for reply, i use a personal homemade supergun with direct CSYNC signal from jamma with a 5k potentiometer, and 1K pot + 220uf on RGB lines.

    Last edited by Jonap; 10-25-2020 at 05:35 PM.

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    . davidmorom's Avatar
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    While I was developing and testing my custom supergun design, I experimented exactly the same interference as you. In my case, it resulted to be a severe ground loop interference, caused by a combination of a very low quality power supply, with insufficient EMI filtering, and cheap AV cable with a high impedance shielding (about 1 ohm, which is pretty high). This caused a voltage drop across the shielding, which ideally should be an equipotential conductor.

    Replacing the power supply or the AV cable fixed the problem. To be safe, I decided to change both. Now I'm using a Retrogamingcables packapunch cable, a Power Pax SW3110B 5V 2.5A supply for the MVS and a Power Pax SW4310B 5V 1A supply for the OSSC. With this combination the interference is completely gone.

    Keep in mind that if you use an OSSC or another type of digitiser, you also need a good quality power supply for it, otherwise it may still introduce interferences.

    Hope this helps.

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    Quote Originally Posted by davidmorom View Post
    While I was developing and testing my custom supergun design, I experimented exactly the same interference as you. In my case, it resulted to be a severe ground loop interference, caused by a combination of a very low quality power supply, with insufficient EMI filtering, and cheap AV cable with a high impedance shielding (about 1 ohm, which is pretty high). This caused a voltage drop across the shielding, which ideally should be an equipotential conductor.

    Replacing the power supply or the AV cable fixed the problem. To be safe, I decided to change both. Now I'm using a Retrogamingcables packapunch cable, a Power Pax SW3110B 5V 2.5A supply for the MVS and a Power Pax SW4310B 5V 1A supply for the OSSC. With this combination the interference is completely gone.

    Keep in mind that if you use an OSSC or another type of digitiser, you also need a good quality power supply for it, otherwise it may still introduce interferences.

    Hope this helps.

    Thanks for youre reply, interesting info first of all i go to buy a quality RGB shielded cable.
    You think is need 220uf in RGB lines? or really not.

  6. #6
    JammaNationX
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    That's power supply related, did you bridge logic ground and earth ground, that usually gets rid of the problem.

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    . davidmorom's Avatar
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    Quote Originally Posted by Jonap View Post
    Thanks for youre reply, interesting info first of all i go to buy a quality RGB shielded cable.
    You think is need 220uf in RGB lines? or really not.
    They are not needed, but they won't hurt if you place them. Just be sure to correctly attenuate RGB and sync lines to 0.7v peak.

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    Quote Originally Posted by Xian Xi View Post
    That's power supply related, did you bridge logic ground and earth ground, that usually gets rid of the problem.
    What do you refer with logic gnd and earth gnd?
    i ground like this pic:



    Quote Originally Posted by davidmorom View Post
    They are not needed, but they won't hurt if you place them. Just be sure to correctly attenuate RGB and sync lines to 0.7v peak.
    OK i know impedance PCB are needed for dont damage OSC and TV's with scart input, but is need to bypass too for AV encoders like jrok?


    Thanks both for help

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    . davidmorom's Avatar
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    Quote Originally Posted by Jonap View Post
    OK i know impedance PCB are needed for dont damage OSC and TV's with scart input, but is need to bypass too for AV encoders like jrok?
    I don't know about that AV encoder, but for OSSC/Framemeister, or any TV set (and any 75 ohms terminated device, I guess), you just need to place three resistors of about 120 ohms in series with R, G and B, and a 680 ohms resistor in series with sync, to drop the voltage to the correct level. Or you can use four potentiometers and find out the correct value with a scope.

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    Quote Originally Posted by Xian Xi View Post
    That's power supply related, did you bridge logic ground and earth ground, that usually gets rid of the problem.
    Finally found the problem, as you say problem is power supply adapter, i use a chinese one of this:



    I use a PC ATX power supply ( use molex 4 pin conection ) and works perfectly fine without noise.


    Now i need how found a good dc adapter with molex but with quality not chinese for mi supergun, but i dont know where, all seems to be chinese bad adapters in tipical stores ( aliexpress, ebay, amazon... ).

  11. #11
    Kula's Candy
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    Just get a compact PC PSU

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