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VGA cable open?

Discussion in 'Electronic Repair' started by Ray, Dec 15, 2005.

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  1. Ray

    Ray Guest

    VGA cable fault - solved

    We have more than 100 classrooms with ceiling mounted data/video
    projectors. One room recently had a problem with the projector not "seeing"
    the computer. In autosearch, it would flash an image for a fraction of a
    second, then continue searching. Hmmm. Bad sync. Bypassing the VGA cable
    made it work, so we were down to either repairing the existing cable or
    pulling another through the conduit... not fun and very time consuming.
    We usually try for a repair to get a room operational ASAP, but how do
    you find a break in a cable? Most of it is in the wall and not likely to
    be damaged or faulty from the factory which should have shown up right
    away. All I had with me for troubleshooting was my toolkit and o'scope.
    Cables usually break at the connectors, so I had two choices... the
    user end or the projector end. Wiggling it at either end didn't make it
    work with signal on it. Hmmmm. What to do? A TDR would be nice. Perhaps
    cable capacitance could provide a clue. I scrounged a 47K resistor out
    of my toolbox and hung one end on the scope calibrator (half a volt 1kHz
    square wave) and attached the probe to the other end: a quickie low-value
    cap checker. The scope ground was attached to the cable shell and pins
    probed with the scope/resistor combination via a jumper lead at each end
    of the cable. Each used pin showed some capacitance indicated by a
    rounding off the edges of the square wave... all but the one that broke
    inside the connector. Pin 13, a sync line, was open at the projector end!
    Back to the shop for a replacement connector and the room is again
    operational. R&Ring VGA connectors is no piece of cake, but pulling a new
    cable is a lot worse. The original was likely damaged by too hard a pull.

    Ray Carlsen
    University of Washington, Seattle
  2. Dave D

    Dave D Guest

    You can say that again. Ever tried it on a heavy duty cable like on a Sony
    20SF monitor? Fantastic fun, much easier to transplant a cable form a duff
    monitor in that situation, or buy a 5 BNC to 15 pin DSUB, cut the BNCs off
    and fit the cable inside the monitor. I sympathise with you having to fit a
    new plug.

  3. Lynn Coffelt

    Lynn Coffelt Guest

    Good job! I guess I hadn't seen replacement VGA connectors. I would have had
    to splice a short piece of cable with a connector already attached. Messy,
    and perhaps not exactly up to standards, but hey!
  4. James Sweet

    James Sweet Guest

    Radio Shack at least used to sell them, HD-15 connectors. I replaced one
    once on a monitor, it was a royal pain but it worked.
  5. carneyke

    carneyke Guest

    Ray, Cables in conference rooms take a beating. We get our share of bad
    cables and bulbs. We have breakout boxes on the conference tables with
    short VGA cables plugged into them. Replacing a 4 foot on the table
    versus pulling new cables tgrough conduit. The cables on the table take
    a beating. Some rooms go through 2-3 cables a year. We don't seem to
    get the rated hours out of some projector bulbs. Some seem to make the
    2000 hours but some less. We can't pin it down to any make / model. How
    do you find the life of these expensive bulbs ?
  6. Ray

    Ray Guest

    Ray, Cables in conference rooms take a beating. We get our share of bad
    Yep, same thing here. We attach "shortie" cables to the fixed ones with
    gender adaptors so the instructors can't booger up the hard-to-replace ones
    in the wall. I've seen three failed Calrad brand molded VGA cables recently...
    either a bad run or just cheap construction. NO more of those.
    It varies quite a bit and we can't tell the worst offenders ahead of
    time either. Some projectors sit in rooms that are open to outside air and
    suck a lot of dust into their tiny filters. Those (Proxima DP9295 is one)
    need to be cleaned every two weeks or so. The occasional lamp explosion
    doesn't seem to repeat with a new lamp, so I must assume it's just a
    random failure. They push those lamps pretty hard and some are just not
    up to it while others of the same type still work fine at end-of-life. We
    can't predict how long they will last. I have to say that the majority of
    ours do make it to their rated hours.

  7. carneyke

    carneyke Guest

    Ray,Thanks for the reply. We are finding similar problems ! Ever seen a
    brilliant person try plugging in the VGA connector (D shaped) backwards
    ? They get it done too, amazing what it does to the pins ! Sometimes we
    starighten out the pins and it works. We do the gender adapter too ! We
    have some projectors that require a filter cleaning every 150 hours.
    It's a pain keeping up with them as they need a filter reset as the
    lamps do. We have some people that keep resetting the lamp timers until
    it won't fire anymore or the lamp "blows". The filter message requiring
    the cleaning / reset is a good idea but those units never seem to have
    dirty filters ! We have some units that the filters get clogged and
    overheat / shutdown. We can't figure that one out either as some areas
    / models seem to clog sooner than others. We seem to get the life out
    of most bulbs but some just don't make it. We gave up trying to get
    warranty replacement on defective bulbs, suppliers just don't believe
    they fail before the service life or figure we are pulling a fast one.
    We have seen at least 5 bulbs premature fail in the 2-3 years we have
    been servicing these dataprojectors.
  8. simon hanlon

    simon hanlon Guest

    I do a similar short cable when installing projectors, We run the cable in
    PVC Trunking and then use a 12" pigtail to the outlet box, I have seen a few
    bad connectors but I find no problem in soldering new ends on...compared to
    the 50pin d-ways we use to solder on Cheque sorting machines its easy.
    Crimping is probably the easiest way to go
    As for the over heating lamps, how are the projectors mounted? I have seen
    some with mounting plates blocking air vents. Some projectors also have
    different fan settings so you can have it running quiet (hot). I always set
    them to run noisy!
  9. carneyke

    carneyke Guest

    They overheated due to dirty filters. We have more projectors than we
    can service. They don't get the filters cleaned because we can't get to
    them. So, the run until they stop ! Take Care
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