S*TJ MARCH 1982 18
SERVICE TIPS
ROWE BILL CHANGERS
MIDWAY'S
X-Y MONITOR TROUBLESHOOTING GUIDE (PART 2)
WILLIAMS FU PPERS
ATARI COIN DOORS
by TODD ERICKSON
SUMMIT AMUSEMENT
ST. PAUL. MN
Rowe BIii Changers
The bill/coin return button is an assembly that
can cause a few strange problems. The button
activates a microswitch. If the arm on the
microswitch bends, it may cause an intermittent
switch closure. This should be an easy thing to
diagnose. If the switch is activated, the trans-
port will run in reverse. After a short time, the
motor will overheat and then it turns itself off
with a thermocouple. A service call may come
in that that changer won't take any money.
When the service man arrives, it may start
working again. The thermocouple has cooled
and the unit starts working again. There have
been many cases that the operator has decided
to take the board and/or transport in for repair
because of this problem.
Wllllams Flippers
As with any flipper assembly, there are just a
few parts that wear out or break. One of the
most important parts is the end-of-stroke. Any
resistance in these points results in a direct loss
of power. In other critical parts, it pays the
operator to use high quality replacements. The
labor of replacing a part is much greater than
the part itself. An end-of-stroke point may be
partially pitted, resulting in a small loss of
power. This will, in turn, result in a loss of
income. The operator can't afford to replace
points all the time to keep maximum power.
Wico has the only tungsten point for a Williams
pinball. I have used these points for over 7
months with no noticeable loss of power. The
cost is a bit higher, but they will outlast many
sets of silver points. This is the quality we need
on all pinball flippers.
Atari Coln Doors
Atari has just introduced to the industry the
first sensibly sized coin door. The door is
manufactured by Coin Controls of England.
There is also a coin box under the coin door.
This gives the operator more security for the
money inside. There has never been a need for
the big standard sized coin door. The larger the
door, the easier it is to get damaged from hitting
or picking. The looks of this door should not be
confused with the CoinCo door. They are
definitely different. None of the parts are
interchangeable. I have used these doors for
about 6 months without any service calls
except Canadian coin jams. This problem has
been ta.ken care of now, so the rejector will wipe
the Canadian coin or slug. The ramp on the
door is steep so there are no coins hanging up
on the entry. The coin return button does not
stay in. All the bezels are metal so they don't
break when hit. All the doors have stringing
protection.
It seems there are more service calls with
coins in a video, more than other game sources.
I do feel this door is the finest in the industry.
The only criticism I have of it is that there
should be a provision to place a padlock on the
coin box from inside the door. Several other
manufacturers have started using this door
now.
We continue this 3-part article with Part 2 -
Theory of Operation. Part 1 - Introduction,
Symptom Diagnosis, appeared in S*TJ's
February 1982 issue. Part 3 - Troubleshooting,
will appear in our April issue.
*
THEORY OF OPERATION
To understand what goes on inside the monitor,
large general groups of circuits will be examined
instead of laboriously analyzing the branches
and small circuits that make up these groups.
This will help avoid confusion and aid in a basic,
concrete knowledge of what makes up a monitor.
The Power Supply
The best way to begin explaining the innards of
the X-Y monitor is at its beginning, or the inputs
to the monitor. Ignoring the ground or common
tie points for many of the components, which
represents zero voltage, there are 30 volts AC
going in pins seven and ten of PIOO - the input
jack. These voltages meet at DBIOO which is a
device that has four diodes in it. The 30 volts AC
means the voltage and current alternate, or jump
up and down, going positive and negative with
zero voltage in between. DBIOO and the capa-
citors immediately after it make up the power
supply. Most of the circuits in the monitor can't
use power that jumps up and down, since your
picture would do the same thing. DBIOO chops
up the wave form and capacitors C 100andC101
build up the power that DBI()() chops up. The
capacitors then leak it out so the power is smooth
and not varying. If any component fails in the
circuit, the usual result is blown fuses, burning in
this area, or just less power. The power supply
starts the whole ball rolling, but remember that
other circuits build up voltages that can be
tapped for those circuits that need more than this
thirty plus thirty volts AC from the game
transformer.
The "X" and "Y" Amplifiers
Let's go back to the input jack, PIOO, again.
Along with the grounds and the two 30 volt AC
inputs is the "X" and "Y" channel video infor-
mation. The " X" input is about l0voltsAC and
the " Y" input is about 7.5 volts AC . The " X"
channel information represents parts of objects
from LEFT to RIGHT on the screen. The "Y"
channel information represents parts of objects
from TOP to BOTTOM on the screen. To get
complete objects, then, you MUST HA VE
both the "X" and "Y" inputs. If this is so, then
why aren't the input voltages equal? Well, notice
how a T.V. tube is shorter than itis wide? The up
and down voltages ("Y" input= ±7 .5 volts AC)
don't need as much as the side to side voltages
("X" input= ±10 volts AC).
If we divide the picture into four quadrants,
the responsibilities of the " X" and " Y" amplifiers
may be seen more clearly:
The upper left quadrant is represented by
" -X" and "+Y" information.
The upper right quadrant is represented by
"+X" and "+Y" information.
The lower left quadrant is represented by
"-X" and "-Y" information.
The lower right quadrant is represented by
"+X" and "-Y" information.
So let's say your monitor only has the right side
of the picture and the left side is missing. The top
and bottom right of the screen has"+ X", "+ Y",
and "-Y" information. The left side has "-X",
"+Y", and "-Y" information. But since the
right side is O .K., obviously the only information
missing is "-X". Therefore, there's got to be a
problem somewhere in the "X" amplifier.
From PIOO, the "X" or "Y" signals each go
through a resistor and the linearity control of
their respective channels. The Wells Gardner
monitor only has one linearity control per
channel while the Electrohome monitor has two
linearity controls per channel. These controls are
supposed to be set at the factory. But sometimes
they need additional adjusting. The best way to
do this is to get a test pattern on the monitor
screen, remove the glue holding the control
adjustments in place, vary the controls until the
size is right and the lines are nice and straight,
and then re-glue the control adjustments so they
cannot move.
After the linearity controls, the rest of the
circuitry just corrects the signal for the picture
tube and amplifies it. The output power transis-
tors (two for each channel) are heat-sinked on the
bottom or the side of the monitor chassis. These
feed the "X" and "Y" signals in the form of
current to the yoke. The yoke then puts out two
invisible electromagnetic fields or forces . These
fields pull the stream of electrons that is spit out
of the neck of the picture tube to the various
quadrants of the monitor screen where they will
write or paint a picture. Just as you may u~.: a
magnet to pull nails across a table, so does the
yoke's magnetic field pull the electron beam all
over the picture tube screen to write the picture.
The "X" and " Y" information we talked about
earlier is what tells the electron beam WHERE
to write or paint the picture. When the electron
beam hits the phosphor coating on the back side
of the front of the picture tube or screen, the
phosphor glows in proportion to the electron
beam intensity. In other words, the more electrons
in the beam, the brighter the light that comes
from the screen of the picture tube where it is
being hit by the electron beam. This varying
beam intensity is the function of the" Z" amplifier.
The "Z" Amplifier
At pin one of PIOO, the "Z" amplifier signal
voltage is sent to the base of Q504 in the "Z"
amplifier circuit. This circuit amplifies the AC
" Z" signal and is then sent to the cathode of the
picture tube. This varying " Z" signal voltage in
turn varies the intensity of the electron beam
producing at least eight different amounts of
brightness or "eight gray scale steps" as the
engineers would say.
In case the " X" and " Y" signals are missing,
there is a 90 volt DC power failure - from the
high voltage circuitry that feeds the "Z" amplifier,
or if any other missing signal condition should
occur, the "spot killer" circuitry comes on to
effectively turn off the electron beam, thus
keeping the phosphor from being burned. At the
same time, the light emitting diode turns on
informing you of this. If the "spot killer" didn't
come on when any of the above conditions exist,
the electron beam wouldn't be moved around and
the phosphor in the center of the screen would be
burned from the intense electron beam that is