Service manual

Wells-Garnder Color Vector Monitor Guide
Page 3 of 73
HOW DOES A VECTOR MONITOR WORK?
Vector monitors, also referred to by Atari and others as "XY" or "Quadrascan" monitors, are
available in black & white or color. A black & white picture tube has one electron gun that lights
just one type of phosphor (usually, but not always, white). Color tubes have 3 electron guns that,
when the yoke and neck magnets are aligned properly, each hit their own phosphors only, either
red, green, or blue (RGB). Something called a shadow mask is used so each gun hits only one set
of phosphors. There is no inherent difference between the tubes used in vector monitors and the
tubes used in raster monitors; only the control circuitry differs. That is not to say that you can use
any tube in any monitor; there are several different neck pinouts that have been used for picture
tubes so you have to find a tube with a matching pinout first. If you have a lot of screen burn,
you can replace a Wells-Gardner 6100 color vector picture tube with any compatible "off-the-
shelf" 100-degree in-line picture tube that is also used in raster-scan displays.
So far, this has been just basic TV stuff and it holds true for raster monitors too. Now we will
diverge. The electron guns in the neck of the tube emit a stream of electrons that bombard the
face of the tube that would hit dead center if not for the deflection magnets on the neck of the
tube. There are two deflection coils. One for horizontal deflection (X) and one for vertical
deflection (Y) of the electron beam. Consider the center of the screen to be (0,0) volts to the
deflection magnets. If you want to move the beam to the right you put a positive voltage on the
horizontal deflection "X" coil (+,0). A negative voltage moves it to the left. Up and down are
accomplished with positive or negative voltages to the vertical deflection (Y) coil.
The deflection coils are driven with the same kind of circuitry some audio amplifiers use.
Imagine that the game puts out pre-amp analog levels and that the monitor amplifies and displays
the output. There are some vector monitors (the ones used in the Cinematronics games) that are
digital in nature and have a significantly different design. Do not assume that anything discussed
in this document applies to these monitors since much of it does not.
The third portion of a vector monitor is what (at least by Atari) is called the "Z" amplifier, which
controls the brightness. There is a "Z" amplifier for each electron gun, which means that black
and white monitors have only one "Z" amp and color monitors have three.
To draw an asteroid or other object, the game shuts off the Z amplifier (or amplifiers) and applies
the correct vector information to the X and Y amplifiers driving the deflection coils in order to
move the beam to the desired location. Then the appropriate Z amp(s) are turned on to illuminate
the screen and the vectors are modified to draw an outlined asteroid. On most monitors you can
turn the brightness up to the point where the Z amp(s) do not completely shut down and you can
see the full path of the electron beam as it flies around. The designers of Star Wars exploited
these traces when laying out the dots for the star field pattern and the Death Star explosion to
form "connect-the-dot" messages that says, "MAY THE FORCE BE WITH YOU" on odd waves
from 1 to 31 and, "HALLY MARGOLIN RIVERA AVELLAR VICKERS DURFEY" (names of
the programmers and other people involved with making the game) on even waves from 2 to 30
and on all waves from 32 to 99.