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PostPosted: Thu Feb 01, 2018 5:59 pm 
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So I bought a cheap RGB cable for the SNES. It looked awful and was missing detail in bright scenes as in clipping because it's too bright.

I modified it following this http://members.optusnet.com.au/eviltim/ ... nespal.png

I followed that exactly but I used 100ohms instead of 75ohm and 220ohm instead of 180ohm because that's all I have. I also used pin 7 luma for sync instead of pin 9.

But now I get some buzzing in the audio on bright scenes and it doesn't seem to auto switch to AV Automatically like it should. It's exactly like the picture except pin7 and the different resistors. All ground chained together going to pin6.

What might be wrong, any ideas?

Figured out my cable didn't have 12v and I was just connecting a second GND cable to where 12v was supposed to be. I chained the other ground cable to 5 and 6 instead and used the second ground cable as 12v to get the 4:3 aspect ratio. I still have the buzzing audio but at least that's one thing out of the way for now. Is anything wrong with the diagram I have linked or could the different resistors be affecting it?


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PostPosted: Thu Feb 01, 2018 9:59 pm 
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Location: Estonia, Rapla city (50 and 60Hz compatible :P)
Connecting the "12V pin" is for autoswitching. Connecting it to GND or leaving it unconnected results in no autoswitching. Using 5V will restore the function but the TV will go to widescreen mode from it, you need 12V for 4:3 mode. I personally prefer not to connect the signal, usually the TV is on input anyway so there's no extra button press to change aspect ratio.

Now as far as sound buzzing goes, it is caused by lack of shielding around audio and/or video lines. Really cheap cables have no shield at all, so all signals are subject to interference, less cheap cables use shield around ALL the wires which cures any interference problems but causes crosstalk between audio and video which results in the buzzing you hear that changes with how bright are things are on the screen. A good cable shields all the signals AND all the video signals, similar to how good VGA cables work. I use VGA cables to make RGB cables for my machines, they always have shielded RGB signals and usually one more shielded signal that I can use for Composhit/Luma/Sync and remaining for audio and misc signals. No more buzzing or other problems.

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PostPosted: Fri Feb 02, 2018 6:59 am 
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TmEE wrote:
Connecting the "12V pin" is for autoswitching. Connecting it to GND or leaving it unconnected results in no autoswitching. Using 5V will restore the function but the TV will go to widescreen mode from it, you need 12V for 4:3 mode. I personally prefer not to connect the signal, usually the TV is on input anyway so there's no extra button press to change aspect ratio.

Now as far as sound buzzing goes, it is caused by lack of shielding around audio and/or video lines. Really cheap cables have no shield at all, so all signals are subject to interference, less cheap cables use shield around ALL the wires which cures any interference problems but causes crosstalk between audio and video which results in the buzzing you hear that changes with how bright are things are on the screen. A good cable shields all the signals AND all the video signals, similar to how good VGA cables work. I use VGA cables to make RGB cables for my machines, they always have shielded RGB signals and usually one more shielded signal that I can use for Composhit/Luma/Sync and remaining for audio and misc signals. No more buzzing or other problems.


That's not a bad idea tbh. I'll have to start from square one but I do have a few spare vga cables. The cables are very thin alright so I know what you mean. Probably better for me to just make the cable myself anyway. I disconnected the 12v and just sent 5v to 12v for now which causes the 16:9 switching but I wouldn't mind too much as the crt will only be used for old consoles on the one input anyway. I used the second GND cable and it's not as loud but the buzzing still exists so I think as you said it's just the shielding. Similar to cheap electric guitars which have a lot of buzzing due to lack of shielding on the pots and other parts.


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PostPosted: Fri Feb 02, 2018 4:12 pm 
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Joined: Sun Sep 19, 2004 9:28 pm
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Location: Mountain View, CA
steocullen91 wrote:
...But now I get some buzzing in the audio on bright scenes and it doesn't seem to auto switch to AV Automatically like it should. ...

The reason is answered in this video, including examples of what you describe. Watch the ENTIRE THING. DO NOT SKIP AROUND.

https://www.youtube.com/watch?v=HV2cSKhO6v0

You're welcome.


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