What is the vertical sync cable for in the iMac 27" late 2009?

Discussion in 'iMac' started by macpokerstars, Aug 29, 2013.

  1. macpokerstars, Aug 29, 2013
    Last edited: Aug 29, 2013

    macpokerstars macrumors member

    Joined:
    Sep 29, 2010
    #1
    Hi there,

    When I opened up my iMac I accidentally broke the vertical sync cable in it (the hard tip of the cable was ripped off when my screen fell forward).

    But the iMac seems to be working fine without it.

    What is this cable for anyway?
    Is there any risk of using the iMac without it being plugged?

    Thanks in advance.
     
  2. macpokerstars thread starter macrumors member

    Joined:
    Sep 29, 2010
    #2
    Is there anyone who knows about this cable?
    I've tried to search all over forums, but couldn't find anything helpful.

    Thanks in advance.
     
  3. soomster macrumors regular

    soomster

    Joined:
    Apr 15, 2010
    #3
    Does this problem make the screen flicker at lower brightness settings?
     
  4. jaxhunter macrumors regular

    jaxhunter

    Joined:
    Dec 14, 2012
    Location:
    Arizona
    #4
    That cable helps the larger displays stay in sync... i forget exactly what it is staying in sync with (vertical sync doesn't actually tell you much... If you look it up online you'll get a lot of info about graphics cards and v-sync but there is a difference between what the video card is doing and what the display panel itself is doing) but it has to do with signal and voltages on a higher-res, larger display panel.

    Without it you will hear a high-pitched whine from the display and you might get some flickering or more likely what appears to be a harmonic vibration in the image. If you can find a replacement for that cable I would recommend getting it and putting it in as a lot of people cannot handle the noise and visual effect for very long. There was a post on iFixit where someone had repaired his v-sync cable but that may or may not work for you.

    You might also be able to take it to an Apple store and have them replace the cable.
     
  5. soomster macrumors regular

    soomster

    Joined:
    Apr 15, 2010
    #5
    I have 27" iMac mid 2011, recently I broke the plugin on the led backlight board, now the wire is a bit loose in the plugin. Everything works fine I think but sometimes when the screen wakes from sleep or when its on low brightness level I see a little flickering, just like you describe as "harmonic vibration in the image". It's usually goes away after 20-40sec. No high pitch sound. Maybe I should replace the Led Board to be on the safe side?
     

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  6. jaxhunter macrumors regular

    jaxhunter

    Joined:
    Dec 14, 2012
    Location:
    Arizona
    #6
    The mid 2011 no longer used a V-sync cable as it switched to an internal DisplayPort connection which integrated the V-sync into the main display cable. This is the reason you don't hear the whine; it was caused by a disrupted video signal. That particular cable you refer to there is the backlight sync cable. You could replace the backlight board if the socket is the problem. Just make sure to properly shut down the machine before you unplug it. If you don't the backlight board will retain energy and need about 15 minutes after you unplug it to discharge. A proper shutdown commands the backlight board to discharge. But, because the cable is cheaper I would investigate as to whether the cable was the problem or the socket. Could be either one.
     
  7. soomster macrumors regular

    soomster

    Joined:
    Apr 15, 2010
    #7
    Thanks for the answer, the plugin for the "backlight sync cable" is half-broken, the plug fits in but its a bit loose. Do you know what happens if the connector does not connect to the board? Lets say what would happen if this "backlight sync cable" would be unplugged? Would that make the screen flicker?
     
  8. jaxhunter macrumors regular

    jaxhunter

    Joined:
    Dec 14, 2012
    Location:
    Arizona
    #8
    Yes it would.
     
  9. soomster macrumors regular

    soomster

    Joined:
    Apr 15, 2010
  10. rodion15 macrumors newbie

    rodion15

    Joined:
    Sep 14, 2015
    #10
    Hi, I'm a bit confused by your answer: the iMac mid2011 has a V-Sync cable (part number 922-9843 V-Sync/LCD Temp Sensor Cable).
    Do you know where I could get any more info about how this cable works?

    Thank you
     

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