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  1. #1
    2 Star Lounger Diogones's Avatar
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    A question about connecting VGA laptop to TV

    Hello,


    I've been using the Apple DVI to Video Adapter to connect my Mac to my old analog TV, and I must say it works well. However, I've been helping a friend hook up his new HP Pavilion dv5-2135dx laptop with a VGA to the same TV. I ordered a VGA to Composite/RCA Adapter Cable, but after we hooked it up, the only image we got was black and white and quite distorted. We fiddled around with the settings, but could not get it to work. I'm fairly certain (although not 100%) that his laptop supports video out, and the adapter description did say that if the computer supported video out, it would work.


    I've heard that instead of a simple cable, an actual converter box is required, to transmit the signals, like this one. I understand why that would be necessary, but what I'm confused about is, why is it that the DVI to composite adapter from Apple works, but the generic VGA adapter doesn't? They both transmit analog signals (since the video is DVI-I on the Mac I'm using, it has the analog pins) and both are just a direct cable, so wouldn't it work? Unless the Apple adapter has an extra component involved that the VGA cable does not.


    If anyone could explain this to me, I'd appreciate it. It would help to give me a better understanding of how video cables operate.
    Last edited by Diogones; 2011-10-16 at 02:30.
    "Violence is the last refuge of the incompetent." - Issac Asimov, from his novel "Foundation"

  2. #2
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    DVI is Digital Video, but can have analogue output. In your case the mac has both. VGA is neither composite nor svideo, it's 5 lines, RGB and 2 x sync. If you want anything else your computer will have to send the output via some other connector. The HP spec says it has an HDMI connector, I'd use that.

    cheers, Paul

  3. #3
    2 Star Lounger Diogones's Avatar
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    Thanks for the informative reply, Paul! You are correct: the laptop does indeed have an HDMI connector on it, but the TV does not. Would I have to get some sort of HDMI to S-Video or Composite adapter, or would I still need the converter box?

    So the DVI can have analogue output, but VGA doesn't? I thought VGA was an analogue signal?
    "Violence is the last refuge of the incompetent." - Issac Asimov, from his novel "Foundation"

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    VGA is analog but the video card must support a special "TV out" format to broadcast a proper signal to a composite or S-video connector. The MAC adapter probably contains that conversion firmware to do that while the adapter you bought does not. Old video cards would sometimes have the composite video connector built right into it but it was never popular and never gives anything near what would be considered a good quality signal.
    I can only suggest you play with the output settings of your video to the VGA port, but even if you do get it working, VGA to VGA or HDMI to HDMI blows it away by a log or two and is worth the upgrade unless one is really strapped for cash because LCD panels are quite cheap and good quality these days.

  5. #5
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    Video cards with DVI connectors may have analogue output, but it is likely to be VGA which most TVs won't accept.
    I can't find a manual for the HP to tell what signal is output - apart from HDMI.

    cheers, Paul

  6. The Following User Says Thank You to Paul T For This Useful Post:

    Diogones (2011-10-18)

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