Star Tech Journal

S• TJ FEBRUARY 198214
A.M.OA.
School for
Coin Machine
Technicians
The only school that comes
to you! Don Miller travels
with his school and
conducts his courses on
video & pinball machines
wherever sponsored by the
A.M.O.A. or state
associations. For further
information contact the
Amusement & Music
Operators Association at
312-726-2810 or Don
Miller at 303-686-7801.
Strong,
Reliable
Joysticks
• Will fit in Upright
and Cocktail Tables
• We ship from stock
Newport
Model 125
Made in the U.S.A. for the
needs of the American Market.
Will replace joysticks in im-
ported and domestic machines.
Interchangeable gateplate for
two, four or eight positions.
Engineered and built to last!
All parts easily replaceable.
FAST SERVICE.
Ideal For
PAC•MAN Games
Joysticks ordered at A.M.O.A.
should be reordered direct from
us.
CALL TODAY
SATISFACTION
GUARANTEED
Newport Machine Design
P.O. Box 418
Bishop, CA 93514, U.S.A.
(714) 873-4431
MIDWAY'S
X-Y *MONITOR* TROUBLESHOOTING* GUIDE* (PART 1)
This
Part
Part
Part
begins a 3-part article.
1 - Introduction, Symptom Diagnosis
2 - Theory of Operation
3 - Troubleshooting
Introduction
Welcome to the world of the X-Y monitor, an
electronic device that strikes terror into the heart of
many a technician. The main reason it is so
intimidating is that the Vector Beam, Quadrascan,
or X-Y monitor is TOTALLY UNLIKE the
Rasterscan monitor, or T .V. set as you probably
call it. Since many technicians are generally un-
familiar with the circuit operation, they may not be
able to figure out when a symptom correlates with
(points to) a particular circuit. If you are a technician,
this information will certainly be a life-saver (a
modest opinion). If you don't know anything about
electronics, just relax, because these monitors are
a lot simpler than a regular monitor or T.V. set.
Vectorbeam or X-Y monitors are used because a
regular Rasterscan monitor constructs the picture
in a different way. For example, your T.V. set has
5 25 horizontal lines on the screen from top to
bottom. Each line is a slice of the picture. If you
stare really close at the edge of a picture of a curved
object (a large ball) or an angular object (the peak
of a root) on the screen of your T.V., you will be
able to see the individual slices that the object's
edge is made up of. The edge of the curved or
angular objects will not appear to be completely
smooth, but will look like they are stepped. How-
ever, at normal viewing distance, these same
curved or angular lines will appear to be smooth or
straight and not stepped. To make sure that the
pieces or slices of the picture stay together just like
they were transmitted, T .V. sets have syncronization
circuits. Vectorbeam monitors don't use ANY of
this. Here, the elctron beam smoothly goes any-
where it is told to paint the picture. It DOES NOT
go across the screen 525 times to paint the picture
in slices. Because of this shortcut, the circuitry is
less complex and the detail in the figures will
appear smoother. One drawback is that the bright-
ness level is intentionally designed to be at a level
high enough to burn or etch right into the picture
tube face . This will be covered in more detail later.
If your X-Y monitor develops a problem, you can
go directly to the " SYMPTOM DIAGNOSIS"
section where you can match up your problem to
the problem described and the circuit that may be
causing it. From there you go to the schematic
diagrams for your particular brand of monitor and
troubleshoot the circuits mentioned in the
"SYMPTOM DIAGNOSIS" section.
If you are a technician who is unfamiliar with X-Y
monitors, you will want to read the "THEORY
OF OPERATION" section. This section JS NOT
a rigorous description of circuit operation, but a
simplified general description of major circuit
blocks. Some literature has been written on this
subject. Electrohome's instruction and service
manual on the G05-801 is an analysis on one X-Y
monitor (which Midway Mfg. Co. does not use)
described from an engineering standpoint. All
that is necessary to understand it is a battery of
U.N . interpreters! Electrohome's instruction and
service manual on the G05-802 and G05-805
monitors (which Midway Mfg. Co. does use) is
simpler and more condensed. The best manual we
have found on the subject so far is Wells Gardner's
publication on their Graphic Display Unit, model
19V2000 (which Midway Mfg. Co. also uses).
Most technicians will understand it and it is very
complete. The above manuals are available on
request from your distributor or monitor
manufacturer.
For those who know nothing of electronics, we
suggest that you read the "THEORY OF OPERA-
TION" section, and we definitely recommend that
you read the "TROUBLESHOOTING" section.
Symptom Diagnosis
1. Insufficient width or height:
A. Horizontal line ( due to "Y" amplifier
defect).
• Bad yoke.
• Bad "Y" amplifier output transistors.
• Blow "Y" amplifier fuse.
• Open fusible resistor in the "Y" ampli-
fier.
• Yoke pins not making good contact
(very common).
B. Vertical line ( due to "X" amplifier defect).
• Bad yoke.
• Bad "X" amplifier output transistors.
• Blown "X" amplifier fuse.
• Open fusible resistor in the "X" ampli-
fier.
• Yoke pins not making good contact
(very common).
2. Picture spread out too far and/ or crushed in
certain areas:
A. Controls for linearity (located on the
deflection board and ~et at the factory) are
rnisadjusted.
B. Bad yoke.
3. Poor focus:
A. Low focus voltage from the high voltage
board.