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TV Oscilloscope Almost Done

Discussion in 'Electronic Design' started by T.C. Mann, May 23, 2008.

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  1. T.C. Mann

    T.C. Mann Guest

    I just converted a 5" B&W TV into a very basic oscilloscope. I now
    have a nice steady 60 Hz horizontal time base and can deflect the
    vertical trace full screen with just 200mA @12V. The last item I
    would like to improve is the keep the electron beam at a constant
    voltage. Right now, the beam intensity varies based on the received
    picture information. The little PCB on the back of the CRT neck has
    only 4 wires going to it and 2 of the wires would have to be for the
    heater. Could one of the other wires simply be tied to a constant
    voltage source through a pot so I can vary the brightness or is there
    a better way of doing this? Thank You - T.C.
  2. Tim Williams

    Tim Williams Guest

    Might be. Trace the circuit, there can't be much there. With only four
    wires it's probably amplified video going right to the grid or cathode.

  3. T.C. Mann

    T.C. Mann Guest

    I should have mentioned this is a solid state chassis but I should be
    able to apply the same technique. If I understand correctly, I could
    simply cut the circuit supplying the video signal to the base of the
    video amp transistor (assuming a common-emitter configuration) and
    then hook it to a constant voltage source via a pot. Since I don't
    have a schematic for the set and it's kinda cramped working in that
    area of the PCB, it's probably easier just to vary the voltage
    directly at the cathode simply because it's easier to get to. Thanks
    for the suggestions, though - T.C.
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