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Dim display Panasonic stereo

Discussion in 'Electronic Repair' started by Ken G., May 20, 2007.

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  1. Ken G.

    Ken G. Guest

    This is a typical 5 disk 2 tape deck bookshelf Panasonic stereo with a
    multi color florescent type display .
    It is about 1/4 of normal brightness . Any way to fix this ?
    Is it the display tube or capacitors .
  2. Meat Plow

    Meat Plow Guest

    Another monster created by reading in s.e.r that changing caps fixes
  3. N Cook

    N Cook Guest

    These displays are amazingly reliable compared to zebra strip failings etc
    of LCD displays. I've never seen a failed or corrupted one , even
    in a unit thrown out of a window onto concrete, the display, the only bit
    still worked.
    I would check for any -30V or so rail failings then disconnect the 3V or so
    AC feed to the cross wires and try from another source in case leakage in
    the original transformer was producing a problem
  4. Ken G.

    Ken G. Guest

    Thanks . i have replaced capacitors in VCRs before for dim display . I
    have seen only a few of these stereos this way and if you ever worked on
    one you know how difficult it is to get apart & under the boards .
    I will note the your ideas and collect more before i dig in .
    Thanks !
  5. JR North

    JR North Guest

    Just like every electrical problem in a car has got to be a 'fuse'.
  6. Guest

    These VFDs typically want +30v for the anode, and filament v depends
    on the display, but is very low. They can dim after 20 or more years
    of use, if its that old I'd suggest a slight filament boost. One way
    is to put a turn or 2 onto the mains transformer secondary and connect
    this in series with the filament feed.

    VFDs have a huge margin on filament power.

    Another poss is to clean up the optical filter, or replace it with a
    lighter one, or even leave it out. With these tricks you should get
    another century out of it, VFDs just dont die.

  7. Ken G.

    Ken G. Guest

    Well thanks again . I dont think this is more than 10 years old . I just
    never bothered trying to fix a dim one like this .
  8. Gary Tait

    Gary Tait Guest

    wrote in
    IME, the filments are grounded, with the segments pulled to ground ot -30
    as needed.
    If the trasnformer is open framed.
  9. Guest

    VFDs are matrixed thermionic valves, and you cant run what is a valve
    mechanism like that. Which bit is grounded doesnt matter, but always
    the anode is positive wrt filament to light it. At only 30v anode the
    grids should be positive to get light output.

    In practical apps the segments are matrix driven, lit one after
    another, so you need to scope it to see whats going on.

    If its not one can typically tweak the filament supply cct to get a
    bit more V.

    But I see this is only 10 yrs old. It may be the display is being
    overdriven, which causes them to dim prematurely. If so, removing the
    usual dark filter and replacing with something lighter, or possibly no
    filter, would enable reduced anode current.

  10. Ken G.

    Ken G. Guest

    I guess its the display tube . Fortunately the power transformer has a
    small board stickng up in plain sight with the 30v circuits and fil.
    circuits on it with the pins labled . All the voltages are fine .

    Strange though .. When i push my finger on the back of the display board
    across solders the conducting of my finger causes the display to go nuts
    and random segments get real bright .
  11. N Cook

    N Cook Guest

    Have you tried cutting the traces to the cross-wires, usually the end ones
    or end pairs and driving from another low V ac source, assuming there is a
    3V or so secondary on the transformer.
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