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NEC 3D image collapsed vertically

Discussion in 'Electronic Repair' started by anonymous, Feb 19, 2007.

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  1. anonymous

    anonymous Guest


    I'm the owner of an old NEC 3D monitor (I bought it around 1988 or so),
    and it was working fine till I stopped using it for a few months and
    switched it back on yesterday... Suddenly, the image collapsed vertically:
    the bottom half is still readible and apparently not too distorted, but
    the top half lines have collapsed to a mere 3cm high band, in which the
    text even appears inverted (upside down) for the top lines.

    I opened the monitor and checked for the trimmers (dirt may sometime be
    responsible for false contacts) and for any defect that would be visible
    (exploded or leaking capacitors, burnt resistors, diodes or transistors),
    but I found nothing wrong. Before I spend more time investigating, did
    anyone else already encounter such a problem and/or could give advice as
    to where to direct my investigations ?

    This monitor is the only one I got that is capable of displaying old
    computers images (15Khz Hsync), and I do need it...

    Many thanks in advance !

    Thierry Godefroy.
  2. Guest

    I'd start by getting a circuit diagram, then you can check varous
    voltage points in the horiz scan section.

    none of your newer ones will do 15kHz horiz? I'm surprised, most bog
    standard 17" ones will do that.

  3. Franc Zabkar

    Franc Zabkar Guest

    Look for dry electrolytic capacitors in the vertical section.
    Otherwise, if your chassis uses discrete transistors for the vertical
    amp, then check those. The worst case scenario is a bad yoke.

    - Franc Zabkar
  4. Or if you want a working NEC 3D I'm about to toss.....

    --- sam | Sci.Electronics.Repair FAQ:
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    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
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  5. James Sweet

    James Sweet Guest

    Not any I've seen that were made in the last decade or more. The last
    VGA monitor I had that was capable of 15 KHz was a Sony CPD-1302 made
    circa 1988.
  6. b

    b Guest

    anonymous ha escrito:

    classic symptoms of bad caps in the vertical section. just replace

  7. Guest

    I stand corrected, had forgotten to take interlacing into account. Can
    the OP not use a TV?

  8. anonymous

    anonymous Guest

    Thank you (and everyone else) for your advice. I indeed think it has
    something to do with a bad capacitor or transistor... Alas, without a
    schematic, it's like searching with blindfolded eyes. I therefore wrote to
    NEC, and I hope they will provide me with a schematic...


    Thierry Godefroy.
  9. Franc Zabkar

    Franc Zabkar Guest

    I don't know if it's the same beast, but a service manual with
    circuits for an NEC Multisync 3D (model JC-1404) is available for free
    download (in four parts) from here:

    If your monitor has an LA7835 vertical output chip, then change the
    capacitors nearby.

    - Franc Zabkar
  10. anonymous

    anonymous Guest

    WOW ! Cool ! Many thanks: that's excatly what I was searching for ! :)

    Best regards,

    Thierry Godefroy.
  11. jonpi

    jonpi Guest

    was this the one that the electrolytic capacitors leak and hurt traces
    on the multi layer main board...

    if you see physical, electrolyte leakage on the board, it is, and you
    must be careful because the traces are very small ... usually require
    jumping some with wire...i tried to get one going once like this and i
    gave up ... the degree of damage can vary alot and mine was a pretty bad one
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