Which VGA is being used when connected to an external display?

Discussion in 'MacBook Pro' started by tandokos, Aug 24, 2014.

  1. tandokos macrumors newbie

    Aug 23, 2014
    Hi guys, I have this red horizontal lines problem instead of black. I try to connect my macbook to an external display using HDMI to check whether my VGA is okay or not. It turns out that the display is okay on external display, no red at all. Does it mean that both of my VGA is okay? Or maybe one of them is not okay?

    Oh and two vga of my macbook pro 15" are intel hd and amd radeon hd

  2. snaky69 macrumors 603

    Mar 14, 2008
    VGA is either a type of cable or a very old(1987) type of graphics card called a "video graphics array". Since you have neither on a macbook, I'm going to assume you are talking about your GPU (graphics processing unit).

    Your MBP, if I read you correctly, has two GPUs. The first one is integrated to the processor and is used to for low-power operations when things being displayed aren't too complex.

    The second one is an ATI card used for more complex images, such as games, and is the only one connected to the display out port on your mac. If you have an external display connected, only this card works, not the integrated one.

    My guess is that if you're experiencing red lines on your display but nothing shows up on an external, the ribbon cable connecting the display to the logicboard might need reseating or replacing.

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