TV Scribble Vision
Do you know how to make full scribble pattern on your television? Starting a scribble-vision mode on your TV is really easy and can be achieved by reading this article.
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.
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.
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.