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    MEMBER NAME: TVCABLE                                  *
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                         S C R I B B L E V I S I O N

                                 11-MAY-90

  If you open the back of a TV, there's the neck of the picture tube sticking
  out the back. It has a 'yoke' around it that is made of two large
  saddle-shaped coils, usually of lacquered copper wire. Sometimes the coils are
  wrapped in tape or plastic or an insulation of some kind, but they're usually
  just copper.

    _____
   |     \   Yoke (wraps around tube neck)
   |      \  =====
   |       \-----------\-|
   | Picture Tube      |-| (plug on END of tube neck remains connected)
   |       /-----------/-|
   |      /  =====\
   |_____/   Yoke  \ Wires from YOKE to CHASSIS
                    \ (cut these and connect YOKE to STEREO)
                     \
                      \ (leave the CHASSIS end of the wires UNCONNECTED)
   -------------------------
  | TV Chassis              |
   -------------------------


  OK. Sometimes there is a bundle of wires or a multi-wire cable that goes from
  the yoke coil to the chassis. (the yoke coil defects the light spot back and
  forth so that it scans out the TV picture. Check an encyclopedia or TV repair
  book at a library for illustrations or block diagrams etc. if this isn't
  clear) anyway, the yoke coil will be connected to the main chassis/circuitry
  of the TV set by several wires, sometimes there's a cable connector or
  multi-pin plug/socket arrangement on the end. What you have to do is
  disconnect ALL wires that lead from the chassis to the yoke coils (do this
  with the TV _OFF_ : HIGH VOLTAGE!!!). If the yoke wires have a connector,
  just unplug it from the chassis. If the yoke wires are soldered on to the
  chassis you will have to cut them. There will also be wires running from a
  plug/socket on the very end of the neck of the picture tube. Leave these
  connected - they are needed to warm up the picture tube so you get an image
  on the screen.

  Now,  turn the tv on and carefully touch a pair of speaker wires connected to
  a playing stereo, (or just run a 9 volt battery over to the yoke wires) try
  out various pairs of wires until you see the spot of light that will be in
  the center of the TV picture (you have disabled scanning and should only see
  one dot on the face of the picture tube) uh, try connecting voltage or
  speaker audio into pairs of yoke wires until you have determined which two
  pair of wires move the dot vertically and which pair move it horizontally.
  You can use a mirror to watch the TV while fiddling about in back with the
  yoke wires. Once you have determined the vertical and horizontal pairs, just
  run a set of speaker wires from your stereo over to the yoke pairs and turn
  up the volume, and adjust the left-right balance until the music or radio you
  are listening to makes the screen scribble around and pulsate to the music.

  If you have an oscilloscope, it's even easier - just put the oscilloscope in
  X/Y mode and feed one channel of a walkman into the horizontal probe and the
  other channel (left/right channels here) into the vertical sweep probe. The
  oscilloscope will display a scribble of the music coming from the walkman.

  Old black and white TVs work better than color TVs for making scribble
  visions. The only requirement is that light appears on the screen when you
  turn on the TV set (that is, you can see the scanning pattern). You may have
  to adjust contrast and brightness to get the best scribble trace on the
  screen.

  If you are using a 'good' TV you might want to install DPDT switches to switch
  back and forth between scribble and normal TV modes. Make sure the DPDT
  switches isolate the chassis scanning signals from your stereo completely or
  you can blow things out.


       This is a diagram of the contacts on the bottom of a DPDT switch.
       Make two of these, one for the Left/Horizontal Yoke-to-Stereo
       connections and one for the Right/Vertical Yoke-to-Stereo connections.
       You only need to do this if you want to switch back and forth
       between TV and Scribblevision modes. Make SURE the Chassis wires
       will get connected to their original corresponding Yoke wires when
       the switch is flipped.

                                 |wire to Yoke Coil
                                 |
                       ------o   o   o-----
     wires from chassis                   wires from stereo
                       ------o   o   o-----
                                 |
                                 |wire to Yoke Coil


  You can also reverse the leads from the chassis to the yoke to make the TV
  display a mirror image or upside-down picture. Mirror reversal is convenient
  if you don't want to be forced to read adversizement graphics when they
  appear on the screen.

  Oh, if you watch a mono audio source in scribble-vision mode, you will just
  see a diagonal line instead of a full scribble pattern. You might have to
  adjust the tone controls on the stereo in a wierd way because bass sounds
  make larger patterns than treble sounds, but treble sounds produce more
  complex textures. Experiment around.
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