Atari Vector Monitor Repair/Upgrade


[Document Version: 6.3] [Last Updated: 8/1/96]

Chapter 1) Introduction

  1.1) About the Author


Author: Gregg Woodcock
E-Mail: woodcock@nortel.com
version 6.3 (8-1-96)

  1.2) Official CYA legal warning and waiver

Although I have made every effort to be precise, this article may contain errors. Even if it does not, some people may still damage their machines or themselves while using the information found in this document. The author is neither responsible nor liable for any damage or injury resulting from any use of this document. The author makes no guarantees of any kind; USE THIS INFORMATION AT YOUR OWN RISK.

  1.3) Copyright Information

This article is Copyright worldwide 1991, 1996; all rights reserved.

I have gleaned a lot of the information included herein from copyrighted materials released by various entities (a few are even included virtually word for word). The hardware we are discussing is "obsolete" in the sense that it is no longer being made, sold, supplied or repaired by Atari or Wells-Gardner. I have talked to technicians in both companies who, off the record, applauded my efforts and feel that their respective employers couldn't care less about items this old and "useless". In that light, I see my inclusion of this information as "fair use" (not in violation of the "spirit" of copyright law) in the sense that this document may be the only way for many people to repair their equipment.

I apologise in advance to Atari, Wells-Gardner, Star*Tech Journal, and Play Meter for any perceived violation of the "letter" of copyright law.

In sections where I have transcribed documents word for word (indicated by a line of equals sign characters "=..=START=..=" on the top and "=..=STOP=..=" on bottom), text inside square brackets ([]) is my commentary and was not in the original article.

STAR WARS is Copyright (c) 1983 Lucasfilm, Ltd. and Atari, Inc. All rights reserved. Trademark of Lucasfilm, Ltd. used by Atari, Inc. under license.

  1.4) Distribution Rules

Reprint permission is conditionally granted to everyone. For publications, the conditions are that (1) I am to be notified before the article is printed, (2) I must be credited and (3) I must be sent a copy of the publication in which this article appears (customary free-lance compensation would be greatly appreciated, too, but is not required). Obviously, publishers/editors will need (and are granted) the right to edit the text; I ask only that it be clearly indicated that the text was abridged or altered (no specifics required). Personal (private) use and distribution is unconditional as long as the ENTIRE text is included (additions are acceptable provided they are clearly marked as such). Fair use applies for all; it is OK, to pull small sections of appropriate text out to be given to people who need it without wasting your time by crediting the source.

  1.5) Ackowledgments

I'd like start off by thanking Rick Schieve (rls@intgp1.att.com) for helping me get started in collecting and for donating a file which was the seed for this document.

If this article does not suit your needs, there is probably more technical information (which I have not seen) about vector monitors (of all types) available from Star*Tech including a CD-ROM with 16 years of articles on it!

Coin-Op Games Resource
Decades of Service: Est. 1979
Downloads, Manuals and CD-ROMs
Free InfoPak and Online Tech Forum

  1.6) Have and Want

Before you ask, I do have a small cache of spare vector monitor parts ranging from entire monitors, to individual PCBs, to discrete elements (like the HV transformer) for both color and black-and-white units (no Amplifone parts, though; sorry). I am willing to sell or trade so just send me some email or call me at (214) 684-7380. Also, please call me before you junk any vector stuff; I hate talking with operators and hearing, "I threw all that junk in the trash a few weeks/years ago!" If I can't get there to personally take it off your hands, I can make some calls to friends around the world who will be able to. There are quite a few of us nuts who just love these old vector games.

Chapter 2) How does a Vector monitor work?

Vector monitors, also referred to by Atari and others as "XY" (ick) or "Quadrascan" (double ick) monitors, are available in black and white or color. A black and 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 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 section 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 amp (or amps) and applies the correct vector information to the X and Y amplifiers driving the deflection coils 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) don't 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 starfield pattern and the Death Star explosion to form "connect-the-dot" messages that say, "MAY THE FORCE BE WITH YOU" on odd waves from 1 to 31 and, "HALLY MARGOLIN RIVERA AVELLAR VICKERS DURFEY" (the last the 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.

Chapter 3) How does that help me with repair?

What I have 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, 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 supplies. One of the main root causes of color vector monitor problems is game lockups causing the monitor to go extended periods with no input signal which fries it in short order. The 2 main problems I have seen for game board lockups are bad solder joints on the inter-board connectors (mainly Tempest) and also noisy power supplies. I suggest that you replace the power supply filter caps with 105 degree Celsius capacitors instead of 85 degree ones; the higher temperature caps last much longer and are more stable.

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 transistors used in the final stages of amplification. The Atari vectors use a push/pull rearrangement with NPN and PNP transistors for both the horizontal and vertical amps. 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 the Atari stuff that is very important called the spot killer. What the spot killer does is shut down the Z amp(s) if the X or Y circuits go bad enough to cause the beam to fail to move around the screen enough to keep from burning the phosphors around the zero axes. 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 also lights 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 so it does not always indicate a monitor failure.

Along these same lines the P324 version of the Wells-Gardner and all Amplifone HV units have 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 meant to keep your tubes and other components (such as the high voltage transformer) from being destroyed in the event of a failure causing very large high-voltages.

Chapter 4) How do Wells-Gardner and Amplifone differ?

Atari used 2 different (but pinout compatible) versions of the color vector monitor. The first and most unreliable was the Wells-Gardner. The second (used only in Star Wars and dedicated Major Havoc machines as far as I know) was the Amplifone. There were several versions of the Amplifone, early ones used in Quantum, and later ones used in Star Wars have differing tube/yoke numbers. I'm assuming they are all compatible but don't know for certain? Another quick aside; all the boards and professionally produced documents spell the company name correctly as "Amplifone" but lots of supplemental documentation (such as the document below) misspell it as "Ampliphone". I use whichever spelling was used in the particular document presented.

Each monitor design has a slightly different electrical characteristic and tube shape that will cause games designed for use with the Amplifone to bulge out around the edges (a defect known as "barreling") when using a Wells-Gardner and similarly will cause games designed for use with the Wells-Gardner monitor to cleave inward around the outer edges (a defect known as "pincushioning") when using an Amplifone. It is quite minor and is really only noticeable when in the self-test screen as this draws a (perfectly straight) bounding box around the edge of the display which makes it easy to notice.

The Amplifone uses a neck socket the same as most other (non-vector) monitors from most other manufacturers use but the Wells-Gardner uses a different socket. The pinout, however, is the same so you just need to convert them if you want to switch tubes between the 2 types. If you are careful, you should be able to pull off the plastic neck sockets from the each tube as they are just glued on over the glass. Then just swap them. For example, an Amplifone tube will work in a Wells-Gardner chassis just fine (some versions of the Amplifone manual would lead you to believe they won't but that mistake was corrected in later versions of the manual) except that the display will bulge in the outer-middles slightly. This bulging is due to differences in the yokes and MIGHT be counteracted by swapping the yokes (putting the Wells-Gardner yoke on the transplanted Amplifone tube) but I haven't tried that yet. If you happen to run across a tube cross-reference chart, please let me know what it says about RCA picture tube 19VLUP22 (the Wells-Gardner tube) and Rauland tube M48AAWOOX (the Amplifone tube).

It is pretty easy to check to see if your tube is bad (it doesn't happen a lot but it does happen). Pins are counted counter-clockwise starting at the gap (when looking at the backside of the tube). Pins 9 and 10 are at either end of the heater element. If you want to be absolutely certain about which pin is which, check the socket on your neck board (it should number all the pins). The heater is basically a very low wattage light bulb that emits the electrons which are shot at the phosphor to make light. You should read a short (OK, not a short but a VERY low resistance) across pins 9 and 10 if your heater is OK. If you read an open, your tube is toast and there is nothing you can do (your light bulb is burned out). If your heater is OK, check to make sure that the heater pins are not shorted to any of the emitter cathodes (pins 6, 8, and 11). If you see a short then your tube has a serious problem but in many cases the short can be burned away. Call your local TV repair shop to see if they can "rejuvenate" it.

  4.1) CRT (neck) pinout

Here is the complete pinout of the neck/tube.

  1. G3 (focus grid)
  2. not used
  3. not used
  4. not used
  5. G1 (control grid)
  6. G (green cathode)
  7. G2 (screen grid; brightness)
  8. R (red cathode)
  9. H (heater)
  10. H (heater)
  11. B (blue cathode)

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