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Author Topic: Combining two VGA outputs together  (Read 9973 times)

wingman123

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Combining two VGA outputs together
« on: April 24, 2009, 12:24:59 PM »

I have quite a unique situation concerning my video card. I've posted this question on several other places but didn't get a satisfactory answer.
I have a GeForce 7900GS card. It has dual DVI outputs which I convert to VGA for my analog monitor.

The problem is this:
Some time back, suddenly the colors of the VGA card went all wrong. In one DVI output, red is displayed as black and in the other, blue is displayed as black and the picture is all yellowish. I've used different monitors and have plugged the card in different machines but the output is the same, so I'm sure that the problem is with the card. The warranty period is over so I can't get the card replaced.

What I want to know is, since one output is missing Red and the other is missing Blue, would it be possible to somehow connect the two outputs together to get proper colors for one monitor? Does anybody think this can be done? If so, how?

I'd really appreciate some help because I can't afford to buy a new VGA card right now and I need to play some games.

Thanks in advance.
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urgannagru

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Re: Combining two VGA outputs together
« Reply #1 on: April 24, 2009, 12:35:07 PM »

Well I know its easy to clone the signal coming from an Nvidia video card to both monitor ports. I believe the VGA signal has the color channels separated on different pins, so in theory I think you could wire up a custom cable to do what you want.

What I am not sure about is the electrical side of things, how to do it, or if the computer would recognize said cable as valid.
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pinkpanther

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Re: Combining two VGA outputs together
« Reply #2 on: April 24, 2009, 03:39:16 PM »

To backup what urgannagru said:
http://www.theavguide.co.uk/view_page.php?page=18

So, as far as I can tell, yes it is possible.  And, assuming of the course the next question is "where do I buy the ends?", digikey, McMasterCarr, Jameco, etc.

You'll have to wire both sets of refresh rates into the same header, otherwise you can split the colors as needed.   Make sure to carry a common ground just in case.  Good luck.
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wingman123

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Re: Combining two VGA outputs together
« Reply #3 on: April 25, 2009, 02:14:19 AM »

I guess the first step would be to get both ports enabled, because a port isn't enabled unless a monitor is connected to it. Any idea how to get this done?

The article at http://pinouts.ru/Video/VGA15_pinout.shtml mentions 3 ways of monitor detection. Would any one of them work with my VGA card? For example, according to the first method, grounding the pins 4 & 11 while 12 is disconnected would tell the card that a color monitor is connected. Would that get that port enabled? Or, will I have to use DDC1/DDC2? If it's DDC2, how do I deal with the bidirectional line?

I don't know a lot of electrical stuff, so it would be most helpful if somebody could tell me how to do it at the level of "connect pin 1 of VGA port 1 to the pin 1 of the monitor, etc.".

BTW I wouldn't mind taking a risk, especially when it comes to the VGA card, so experimental stuff are welcome (as long as I can understand what you are asking me to do :) ) .
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