Service manual

Wells-Garnder Color Vector Monitor Guide
Page 4 of 73
Multiple intensities are achieved by selectively reducing the output power of the Z amplifier(s).
The lower power output, the brighter the screen illumination.
The first black & white vector hardware (Lunar Lander, Asteroids, etc.) allowed the game
companies like Atari to produce high-resolution 768 by 1024 images. This was in the late 1970s
when the gaming industry was just moving over to color monitors. Dave Theurer programmed
the first color vector game, Tempest, specifically for a color vector monitor, but the color mask
on color monitors did not permit the same high resolution. Additionally, since you cannot
completely fill the screen with color on a vector monitor, vector games died with the advance of
raster color games. Poor reliability was only a minor concern for the game companies.
How Does That Help Me With Repair?
What has been described so far applies to all vector monitors. Knowing how these things work
helps greatly in trouble-shooting. For instance, deflection of the beam to the edges of the screen
puts the greatest strain on the X/Y deflection circuits, so if you monitor has problems at the
edges of the screen, something is weak in that area. The monitors make their own positive and
negative DC from AC inputs so a reasonable thing to check would be the power supply. One of
the main root causes of color vector monitor problems is a game lockup causing the monitor to
go into extended periods with no input signal which fries it in short order. The two main
problems for game board lockups are bad solder joints on the inter-board connectors (Tempest)
and also noisy power supplies. You should replace the Audio Reg II power supply filter
capacitors with 105 degree Celsius capacitors instead of 85 degree ones; the higher temperature
capacitors last much longer and are more stable. The “Big Blue” capacitor in the transformer
assembly should also be replaced as it causes numerous problems as it fails.
Vector monitors are also fussy about the quality of certain transistors. The X and Y deflection
circuits are very much like audio amplifiers and tend to be hard on the big “bottle cap”
transistors used in the final stages of amplification. The Atari vectors use a push/pull
arrangement with NPN and PNP transistors for both the horizontal and vertical amplifiers. If you
lose one of these transistors, you lose deflection in 1 of 4 directions depending on which
transistor goes out.
There is another circuit in vector monitors that is very important and is called the spot killer. The
spot killer circuit turns off the Z amp(s) (i.e., intensity of the deflection beam) if the X or Y
circuits fail to cause enough deflection of the beam. The phosphors will become permanently
damaged if the beam stays in one place for too long. When the spot killer is active a red LED on
the deflection board lights. The spot killer is activated if the logic board does not supply the low
level X and Y signals for the monitor to amplify, or if the voltage supply for amplification is not
present. Therefore, the spot killer does not always indicate a monitor failure.
Along these same lines of protection, the P324 version of the Wells-Gardner has a circuit known
as the over-voltage protection circuit. This circuit monitors the voltage at pin 4 of the focus
assembly. If this voltage increases beyond a tunable threshold, a transistor fires turning off the
oscillator. This shuts off the high-voltage power supply and completely kills the picture. It is