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DVI, DFP cabling, Pendant relocation....

Discussion in 'Electronic Design' started by Existential Angst, Apr 27, 2013.

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  1. Awl --

    This is Round 2 of trying to get the screen of that re-located Haas
    controller to work right (previous thread CNC display problem...).
    The extension cable is sort of ok, but iyr, the 35 ft replacement DFP cable
    really degraded the screen image. Usable, but irksome.

    So I ordered DFP to DVI adapters for each board, and figgered I run a DVI
    cable in between, since they are readily available.

    No go. The screen displays NO DATA whatsoever, just full-screen blinking
    solid colors.

    On a lark, I started ohming stuff out.
    The original haas 13 ft dfp cable ohms out at 0.8 ohms (0.4 on the shield).
    The 35 ft replacement dfp ohms out at 2.1 (0.3 on the ground).

    So the ohm diffs on the dfp cables would explain some of the screen
    problems, I imagine.

    Here's where it gets inneresting.

    The DVI cables (the 25' I bought, one I have laying around), well, ohms is
    more-or-less moot: Half the pins aren't even connected!!!!
    And the pattern is different between the two DVI's I have!!!
    Of the ones that did ohm out, the 6 ft cable measured a reasonable 0.3 ohms,
    while the 25 footer measured a whopping 4.5 ohms!!! DOUBLE the 35 ft dfp
    cable.
    I'm surprised the screen even showed colors!!

    So my basic Q is:
    Can I get a DVI cable with ALL 24 pins connected?? Which is a minor problem
    in itself, as the DFP is 26 pin, so I have to hope that I luck out,
    connection-wise. I'm pretty sure not all 26 dfp pins are actually utilized,
    but the unanswerable Q for me is, Which ones?

    Ultimately, I may just get a second dfp cable -- or two -- from Haas, and
    splice them together. Is this actually a better solution than muckymucking
    around with dvi-dfp adapters, and dicey dvi cables?

    I would like to use a fem-fem dfp coupler so I wouldn't have to splice the
    dfp, but I can't find any online and I don't know much about the type of fem
    connectors used on the board so I could make a coupler, but I don't know
    what to search on, or if I'll be able to find those. What would I search
    on?

    Never a dull moment.
     
  2. If I splice two haas cables together, the ohms will be 1.6. That's getting
    up near the 2.1 ohms of the 35 footer, so if ohms/impedance is the issue
    here, I'll have a worse image than the original haas single cable, but
    better than with the 35 footer. A reasonable conclusion?

    Does it make sense to put a booster gadget in the splice? I guess the Q
    would be, How many wires is it boosting??
    Also, I don't want to fry any boards....

    Dat splice will proly wind up being the size of a tennis ball.... LOL
     
  3. What I would do is to get a DFP cable from Haas, cut it to two pieces
    and look at the wires in the cable. Any coax cables inside? There are
    special cables with twisted pair, normal wires and coax cables in the
    same cable. Can you get a wiring diagram? Then wire-by-wire add an
    extension between the cut ends - making any coaxes or twisted pairs
    extended with same type cable. This would be the way to go, IMHO.

    If you get the wiring diagram, use pieces of coax or such with
    correct impedance for video signals. The ohms is not really important
    between ends of wires, but the impedance of the cable. For example,
    video coax is usually 75ohms. You can't measure that with any simple
    measurement.

    Kristian Ukkonen.
     
  4. As I think about it, I am definitely getting another cable (or two) from
    Haas.
    Since I'll have to ring everything out anyway, all the wire types and
    impedances MUST match, and that should be the best solution -- tennis
    ball-sized splice notwithstanding. Altho with the right shrink tube, mebbe
    not so bad.

    Had I known about this wide variability in pinouts, cable construction,
    etc., I'da bit the bullet gone the haas splice route from the gitgo.
    The fly there is that Haas is not easy to deal with. Not spitefully
    terrible, mind you, just a lot of corporate inertia, left hand/right hand,
    etc.

    Been an expensive and time consuming learning experience.
     
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