From: email@example.com (richard.l.schieve)
Subject: Raster Monitor Lesson
Date: Mon, 21 Mar 1994 00:54:46 GMT
Keywords: Dusting off another old posting...
There seems to be a lot of monitor related questions and problems
so I thought I'd repost this:
Coin-op video games use one of two types of monitors, vector or
raster scan. Both vector and raster scan 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. This is
just basic TV stuff.
Raster scan techniques are what your basic TV set or computer
monitor uses. Internal circuitry uses the magnets on the neck of
the tube to sweep the electron beam from left to right constantly.
Another circuit moves the beam from top to bottom one scan line at a
time (kind of like the way you read the page of a book). This
scanning goes on all the time, but the electron beam or beams are
only turned on when the desired phosphor needs to be lit. This all
happens so fast that a complete picture appears.
Inputs for most raster scan games include red, green, and blue (RGB)
analog inputs or a single input for black and white. RGB is usually
positive logic, but some Nintendo games use negative RGB logic. For
positive, when the input is turned on, the electron gun is turned on
lighting the phosphor where the gun is pointed at that time. While
these are analog inputs they are often driven with digital logic
gates in various configurations. One RGB input may be connected to
several digital outputs where the intensity of the color is
controlled by how many outputs are on.
The other raster input or inputs are the sync inputs which are
almost always TTL (5 volt) logic levels. Most newer games use
composite sync (just one input) while many old ones use separate
horizontal and vertical sync inputs. Depending on the game,
positive or negative sync may be used. Negative composite sync is
probably the most popular sync scheme used. When converting a video
game to play another games, it is the sync input or inputs that
needs the most attention as the RGB inputs usually just work fine.
For instance, you wish to use an old monitor with no composite sync
input (just separate horizontal and vertical inputs) to work with
composite sync. Usually you can just connect the two sync inputs
together and re-adjust some monitor settings or sometimes just
connect to the negative horizontal sync input. Some monitors have
only a negative logic sync input to use and the logic board only
produces positive sync. In this case you can just add a TTL logic
Sometimes the picture comes out upside down or a mirror image. I've
only seen this with games that use a vertically mounted monitor. I
think the manufactures couldn't get together on which way to rotate
the monitor. In this case the wires to the deflection coils on the
neck of the tube have to be reversed.
There is a whole bag of tricks to use the get things going. Most
newer stuff is getting more standardized (JAMMA, etc.) using RGB and
a negative composite sync from what I've seen, but I work on mostly
This information is all from my personal experiences in working on
arcade video game. If I have stated something incorrectly,
constructive comments would be appreciated (please no flames).
From: firstname.lastname@example.org (-Schieve,R.L.)
Subject: Help With Raster Monitor Repairs
Date: Sat, 1 Oct 1994 18:56:43 GMT
When I first got into collecting arcade videos I found monitors to
be truly daunting. I spent many hours struggling with repairs even
though I had some minimal background in TV repair. I've discovered
several things in the last few years to greatly aid in the repair of
raster arcade monitors even if you have only minimal electronics
skills and I thought I would share the information with those that
The 4 most common raster monitors used in early 80s arcade games are
the Electrohome G07, Wells-Gardner K4600 series, Wells-Gardner K4900
series, and Wells-Gardner K7000 series (this one is much less common
than the other 3). Randy Fromm has spent years of his life helping
educate inexperienced game technicians and the September 93 RePlay
magazine contained one of Randy Fromm's Technical Tips covering
these monitors. There is some text but the article is mostly
troubleshooting flow charts for each of these monitors.
It is an outstanding article! Even without any real understanding
of how a monitor works and only really basic electronics skills you
can fix a host of problems if armed with this article.
The other big thing is the Zanen Electronics (806-793-6337) "Monitor
Get Well Kits" that get mentioned from time to time in this group.
I've installed more of these than I care to count and they work
miracles on distorted and tired monitors. Most of the kits are
under $10 and are made up mostly of electrolytic capacitors
replacing the tired ones that are no longer doing their job in your
I'm not about to try and type in some kind of ascii version of the
Randy Fromm article but I am willing to send copies to you by snail
mail along a listing of the Zanen Electronics Get Well Kits. IF YOU
ARE INTERESTED SEND ME YOUR STREET ADDRESS and I'll drop a copy of
this info in the mail to you.