Extending LCD cable of an iMac 27" A1312 Mid 2011 (art project)

Discussion in 'iMac' started by peter-nwytg, May 2, 2019.

  1. peter-nwytg macrumors newbie

    peter-nwytg

    Joined:
    Feb 24, 2019
    #1
    For an art project I attempted to extend the LCD cable of an iMac 27" A1312 Mid 2011 from its original size to a length of 1, 2 or preferably 3 meters. Eventually the screen is going to be at a distance from the body.

    I couldn’t find a cable longer then 60cm so I came with my own solution but somehow it’s not working.


    My approach:

    The original LCD cable has a 30pin connector on the iMac and LCD side. I’ve cut that cable in the middle and soldered each of the 30 cables of the LCD side and iMac side to a PCB (see image below).

    I soldered IDF connectors to both PCB's and connected both ends of the cable again with a flat cable of the desired length.

    [​IMG]

    I then checked the connection for continuity to make sure all is soldered and connecting well. Also the connections and corresponding resistance match with an original cable. However when the extended cable is installed in the iMac the screen doesn’t turn on whereas the original cable works fine.

    I can't figure out why it would not work.

    In the end results count. Do you know why my approach is not working and how I could fix it or maybe a better (working) or out of the box solution?


    View images of my extended cable and installation in the attachments below:
    cable extension.jpg imac with extended cable installed.jpg
     
  2. jwhazel macrumors regular

    Joined:
    Sep 22, 2005
    #2
    This is an lvds cable. You can’t just splice copper wire the middle and expect it to work because each line has continuity.

    I understand this is an art project, but no clue what the context or requirements are. My advise is to use an external monitor connected via DisplayPort cable from the back. At that point do what ever you need to do art-wise to make it look like it’s the internal one being “detached” if that is somehow a requirement.
     
  3. peter-nwytg thread starter macrumors newbie

    peter-nwytg

    Joined:
    Feb 24, 2019
    #3
    I checked for continuity and everything matches the specs of the original cable, but still it's not working for some unknown reason.

    The requirements are very specific. For the project it's necessary to work with the original parts, some cables may be swapped with custom ones but other than that I have to work with the original parts of the iMac.

    In the end I need an lvds cable of at least 1 meter, preferably 3.

    At the moment I'm in contact with some Chinese cable manufacturers but they take a month at best to produce and deliver and the costs are quite high?


    Therefore I attempted a quick hack and but for unknown reasons it's not working. Continuity and pinout matches the original and resistance is within 1ohm of the original. Maybe it's a matter of shielding / interference of overlapping data lines, length of the cable or something else that I didn't consider that can explain why it's not working?
     
  4. jwhazel macrumors regular

    Joined:
    Sep 22, 2005
    #4
    There’s a lot of things causing it to not work. Crosstalk, inductance, impedance, capacitance, jitter, etc etc.

    https://en.m.wikipedia.org/wiki/Signal_integrity

    Again, you can’t just splice a high speed serial bus line and expect it to work. This is not a hobbyist electronics project with medium voltage where all you need is continuity and things just work. Like any manufacturer, Apple paid a nice chunk of change to a team of engineers to design that cable. It’s not magic, but it’s also not just some bundle of wires at an arbitrary length made from an arbitrary gauge. Without knowing some basic parameters and electrical characteristics of the signal, I wouldn’t expect the Chinese cables to work very well either.
     
  5. Flynnstone macrumors 65816

    Flynnstone

    Joined:
    Feb 25, 2003
    Location:
    Cold beer land
    #5
    Cable handles high frequency signals. Impedance is not equal to resistance. I’m not familiar with the signals/protocol, but if there is an Ack of sorts, then the physical distance is a problem.
    From your pictures, the gray ribbon cable will not work.
    Do you have an electrical engineering department that you can access?
     
  6. Nick [D]vB, May 3, 2019
    Last edited: May 3, 2019

    Nick [D]vB macrumors member

    Nick [D]vB

    Joined:
    Jun 1, 2018
    #6
    With differential signalling the tolerances become tighter as you increase bandwidth, try dropping the resolution / color depth as low as you can and see if your cable works then. If not I'd ditch the break-out boards, track length / spacing on the signal pairs should be sub-mm accurate to minimize timing skew, all those bends aren't helping!

    Maybe try some plastic ribbon / flex with the same pitch and solder directly into the connectors, start short and see how far you can push it. If that fails I'd really just fake it, I think the A1316 / A1407 Cinema Displays use the exact same panel so just pull guts out of one and use a DisplayPort cable to the iMac. Good luck with it!
     
  7. mikehalloran macrumors 65816

    Joined:
    Oct 14, 2018
    Location:
    The Sillie Con Valley
    #7
    The A1316 is the MDP version introduced in 2010. The A1407 was the Thunderbolt version introduced in 2011. Same case. Same display screen as the 2009–2011 27" iMac. The other differences between the two do not matter.

    I see these on Craigslist all the time between $200–$350. No idea what they really sell for except I bet it's less.

    [​IMG]
     
  8. peter-nwytg thread starter macrumors newbie

    peter-nwytg

    Joined:
    Feb 24, 2019
    #8
    Thanks for all the replies. We contacted a Chinese cable factory and they were able to manufacture the cables at the required length. The longest cable shown below is 3m long and works flawlessly at native resolution. I'll upload some photo's of the final setup later on.

    Next up: The extension of the v-sinc cable, the LED-power cords and temperature sensor-cables. 3m iMac LVDS cable.png
     

Share This Page

7 May 2, 2019