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Rejuvenate a VFD display?

Discussion in 'Electronic Repair' started by Ancient_Hacker, Feb 26, 2007.

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  1. I have a really expensive DVM with a VFD display that is getting very
    very very dim.

    A new one from Noritake is $800, so that's a no-starter.

    Any ideas how to pep up a fading VFD display?

    it's the 19-segment alphanumeric type, one line, 20 characters.

    ( It looks identical to the ones on Gilbarco gas pumps. )
  2. Arfa Daily

    Arfa Daily Guest

    You first need to identify whether it is the display itself which is at
    fault, or the circuitry which drives it. Dim displays fall, I would say,
    roughly 50 / 50 into low drive volts, and worn out. Often, the drive volts
    are derived from a voltage multiplier, and it is very common for the input
    capacitor to dry out and go low value, which leads to a low supply. This is
    typically about -30v DC when correct. The filament supply, which you can
    normally measure at about 1.5 to 3v AC, is usually floated on top of
    the -30v, so that is a good place to measure it. Most VFDs have a pair of
    pins at either end of the main row. Measure across these to check the AC
    filament supply, and from either one or the other to ground, to measure the
    negative supply. If these are all in order, then the display is worn out.
    Often, when it is worn out, there will be patches that are brighter than the
    rest. You may be able to squeeze a bit more life out of it by boosting the
    filament supply a tad, but if you go too far, the filament wires start to
    glow a little, and may become visible. Things may be a little different with
    a large 'commercial' display like this, but the basic principles should be
    the same. Do you have schematics for it so that you can see how the drive
    voltages are derived ?

  3. James Sweet

    James Sweet Guest

    Have you checked to see if it uses a standard interface? You may well be
    able to get a cheap aftermarket display that will drop right in.
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