Red LED inside Mac Pro sleep mode?

Discussion in 'Mac Pro' started by Techcomm, Aug 13, 2011.

  1. Techcomm macrumors newbie

    Nov 3, 2008
    I just upgraded to a quad core Mac Pro as my main computer. I have been using a macbook Pro connected to a Dell ultrasharp 24 for a few years and it's so nice to finally have a desktop. What a GREAT machine!
    I noticed that whenever the computer is in sleep mode a red LED is visible through the front of the case. The white LED in the front pulses of course but I just want to make sure the red LED is normal or is it indicating some sort of fault. I tried searching the forum but couldn't find the answer.
    Thanks so much for your input.
  2. Techcomm thread starter macrumors newbie

    Nov 3, 2008
    Just removed the side panel. It's a bright red LED on the riser panel next to the processor. It's only on when in sleep mode. I'm pretty puzzled.
  3. ejosepha macrumors 6502

    Jan 12, 2009
    I had a red light on, but it was when the machine was on and it signaled that one of my RAM barrettes was not functioning. Check to see that all of the RAM installed is functioning. If not, I can't suggest more. Good luck.
  4. Techcomm thread starter macrumors newbie

    Nov 3, 2008
    Interesting Update: From what I found on the net it looks like based on it's location on the board it might be the "processor diagnostic LED".
    I checked and everything inside the case is secure including RAM and all connections. The red LED was on only with the computer off or in sleep mode. The LED was off when the computer was on. I disconnected power to the Pro and the LED was still on. Very Interesting. Where was it getting power?
    Low and behold when I disconnected the mini display port cable (going to my Dell Ultrasharp monitor) the LED went out. When I reconnected the mini display port cabe the LED went on again. I hooked up the monitor using an DVI cable and I no longer have a problem. The LED hasn't lit up since.
    I wonder if the problem was in the minidisplay port cable, the monitor's display port circuitry or ???.
    Anyway, All is well using an HDMI cable.
    I still wonder what was happening and why the LED was lighting up.
    And Thank you Joseph for your reply!
  5. ljonesj macrumors 6502a


    Oct 20, 2009
    Kingsport TN
    it might be a feed back i had a electrical receptacle for my for my ups go out once and it caused any time you touched my mini you could feel a bit a electricity i changed out were the everything pluged in and it was gone so i changed the the receptacle and everything was fine you might want to check that as it could be feeding back through the power into the display port
  6. ifraaank macrumors regular


    Jun 25, 2012
    Odense C, Denmark
    I know this is an old thread, but I have exactly the same problem. Red LED on sleep and when off, and even without the power cord connected :p Computer functions normally otherwise. What causes this? I'm even using UltraSharp monitors as well
  7. Softsand macrumors newbie

    Dec 1, 2016
    I've got this too. Is it potentially harmful to the computer ?
  8. 666sheep macrumors 68040


    Dec 7, 2009
    Some displayport cables sometimes provide current trough DP/mDP port. It goes from display to GPU. That's why LED lights even when power cord is unplugged. There shouldn't be any current, and it could be harmful for GPU port. I'd suggest changing the mDP/DP cable.

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