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Hp Mx70

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    #1

    Hp Mx70

    Yesterday I repaired a 17" CRT HP MX70.

    The problem appeared suddenly after some years of good work: moving the monitor or just knocking on it caused black screen, the image disappeared.
    Sometimes after turn on the screen remained black even if the video signal was present.
    The PS had no problem, the green Led was always on.
    After resoldering almost everything the problem was solved.

    I made this post because when I was cleaning up the PCB, I noticed a big yellow cap: CapXon 3.3uF 50V.
    I had no time to investigate where it was connected, so I would like to ask if someone here knows why it is so large and tall.
    Usually caps in the range of 1uF~47uF 50V have a diameter of 5mm~6.3mm, so I don't understand why this one is so large.

    TIA
    Gianni
    Attached Files
    "In the confrontation between the stream and the rock, the stream always wins...Not through strength, but through persistence."
    H. J. Brown
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    #2
    Re: Hp Mx70

    BiPolar capacitors have no polarity marking (noticed that?) and is MUCH much bulkier.

    It is used in the pincushion circuit in series with a pincushion coil (excited by PWM (there's is a FET on big heatsink near by. The small heatsink with another FET is for the horizontal scan S-cap (row of red poly caps and few more un-heatsinked FETs as well. This bi-polar cap is to "electrically" break this circuit into isolated circuits, bec one is working at low voltage while other side is about several higher voltages from horizontal circuit (within the capacitor's voltage ratings).

    Reason is the construction of capacitor is made of 2 capacitors in series with polaries facing each other as a unit.

    Better monitors doesn't use this cap, instead it uses a transformer.

    Cheers, Wizard
    Last edited by Wizard; 12-06-2008, 05:41 PM.

    Comment

      #3
      Re: Hp Mx70

      Wizard beat me to it. That cap is a bipolar.

      The Toshiba (citizen chassis) with the vertical cap problem you helped me on had a bipolar like that too so thats how I know .

      Ahh no SMT components my dream board .

      On a related note does anyone know why CRT monitor neck boards need all of that shielding when TV CRTs don't?
      Elements of the past and the future combining to make something not quite as good as either.

      Comment

        #4
        Re: Hp Mx70

        @ Wizard: thank you very much for your explanation. I didn't notice the missing negative sign on the cap.

        @ Krankshaft: I suppose because CRT Monitor work at higher frequencies respect to normal TV.

        Ciao
        Gianni
        "In the confrontation between the stream and the rock, the stream always wins...Not through strength, but through persistence."
        H. J. Brown

        Comment

          #5
          Re: Hp Mx70

          And far more sensitive and need to shield magnetic leakage.

          Cheers, Wizard

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