Classic Mode

Coin Slot

Issue: 1982 August 090

Page 45 Text:

Coin Slot Magazine - #090 - 1982 - August [International Arcade Museum]
"r(2)," "r(3)," and "r(4)." A perfect switch, when closed,
would have zero resistance, although a properly
operating switch can have a very small resistance
because nothing is perfect!
Figure 4 also indicates (by "r(1)") that the fuse can
have resistance. Actually, the fuse itself has a very
small resistance that can
be
ignored,
but what I
intended to point out is that the fuse holder can exhibit
a resistance if the fuse does not fit firmly into the
metallic holding clips that provide its electrical con
tacts. This is often a problem in malfunctioning games
(NOTE: Zero Ohms is a short circuit, meaning there is
no resistance to the flow of current. Higher values
indicate increased resistance to current flow, an open
circuit having an infinite resistance, or no current flow.)
To use the Ohmmeter for measuring resistance you
must first select the Ohms function and the lowest
resistance scale (usually called "R x 1") meaning that
the resistance in Ohms can be read directly from the
meter's'Resistance Scale'). The needle on the meter
should immediately go to the high end of the scale
(infinite resistance) since you have an open circuit
and should be checked. The fuse clips should be
between the meter leads. Next, short the two leads
cleaned and bent together so they make good, firm
contact with the ends of the fuse.
together, and the meter should return to near Zero,
While we're on the subject of
_______^^=
since you now have a short circuit between the meter
____^_____
leads. Most meters provide an
resistance, a common and irk
some cause of this phenomena
adjusting know, (usually labelled
'Ohms Adjust'), which can be used
to place the meter exactly on
should be mentioned, that of poor
Zero. If Zero cannot be reached,
contact in 'quick disconnect' con
the meter's internal batteries
should be replaced. You are now
ready to perform the test on one
poor contact causing unwanted
nectors. The typical circuit in a
game usually involves compo
nents physically located in var
of the game's circuits.
(WARNING! the game should
ious areas of the machine (such
as playfield, backboxand bottom
be unplugged when any Ohm
meter testing is being performed
of the cabinet). In order that the
backbox and playfield can be
removed, the manufacturers have
or damage to the meter may
result.)
Figure 4 will be used as an
provided 'quick disconnect' con
-i_(a) example of a typical circuit on
which the Zero Ohms Test is to
be performed. You would first
attach one of your meter leads
nectors in the wiring for all cir
cuits that go from one area to
another (playfield
to backbox,
playfield to cabinet, etc.).
The wiring connecting a typical
(using a clip lead) to the terminal
circuit, such as the one in Figure
on the fuse socket whose wire
provides current from the trans
former (wire color codes and the
schematic must be used to deter
4, may involve several of these
connectors in order to connect
all of the components together
mine this). This point in Figure4 is
labelled "(a)." Next, you would at
in a circuit. Although this wiring
is somewhat difficult to trace(wire
color codes must be used, and
connectors are not indicated on
most schematics) it must be done
in many instances during trouble
shooting a game. If a bad connec
tion is found, the mating contacts
must be cleaned and the socket
adjusted for a tight fit with the
FIGURE 4
TYPICAL GAME CIRCUIT
mating plug pins.
THE ZERO OHMS TEST
Now that we know that various conditions in a game
can cause unwanted resistance in a circuit, how do we
detect it, and if it exists, isolate its cause(s)? One way
(another method will be discussed later) is by what I
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any electronics store
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$20. This is an
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ad
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essential tool
servicing.
When used as an
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w. selectable functions) it measures
Ohmmeter
of
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resistance
http (the kind that affects both A.C. and D.C.
call the Zero Ohms Test. To perform this test you must
have a Volt/Ohm Meter, which can be purchased at
circuits, but not reactance, see note above) in units of
Ohms.
August 1982
© The
International Arcade Museum
tach the other lead of the meterto
the relay coil terminal (point label
led "f" in Figure 4). This is the ter
minal on the coil that is not con
nected to the coil common power
line. Your meter should read in
finite resistance (top of scale)
since the rollover switch is open.
(NOTE: In this example the fuse is shown in the side
of the coil power line that feeds the switches. In many
games the coil common line is fused instead. In these
cases a separate Zero Ohms Test should be performed
between that side of the transformer and the coil
common side of the coil to test for unwanted resistance
in the fuse socket and any intervening connectors.)
The rollover switch would next be closed manually,
at which time the meter should go to Zero Ohms. As
stated earlier, in a properly operating game a small
resistance is normal,
but anything over 1/4 Ohm
should be suspect. If the meter indicates unwanted
resistance, the meter lead attached to the coil (point
Continued on page 46
THE COIN SLOT-45
http://www.arcade-museum.com/

Page 46 Text:

Coin Slot Magazine - #090 - 1982 - August [International Arcade Museum]
Pinball Troubleshooting
Continued from page 45
"f') should oe moved to point "d." If Zero Ohms is then
obtained your problem would be in the circuitry just
eliminated (in this case either the rollover switch or any
intervening 'quick disconnect' connectors).
If, however, you still did not get Zero, keep
with the game's power on and voltages, rather than
resistances, are measured with the Volt/Ohmmeter.
The circuit of Figure 4 will again be used as an
example. To perform a Voltage Drop Test on that
circuit you would first start the game (so that the
"Game Over" relay would be in its normal, unoperated,
condition). Your Volt/Ohmmeter would be set up for
the 'A.C. Volts' function and the lowest voltage scale
moving your meter lead back one point in
selected that has as its maximum voltage reading a
the circuit (to point "c," then "b," etc.) until
voltage over30 Volts('50 Volt Scale,' for example). One
you locate the faulty part of the circuit. You
of the meter leads would be connected to the side of
the coil connected to the coil common power line
should then correct the problem (clean and adjust the
faulty switch or connector), and then retest everything
as two faults could have existed, one masking the
(point 'g" in Figure 4). The other meter lead should be
other.
would then be ready to perform the test.
connected to the other side of that coil (point "f'). You
A word of warning! Your test might seem to indicate a
Next, the rollover switch must be closed by hand, at
faulty switch yet the problem could be in a connector
which time the meter should register a voltage. If the
that is between the point you are testing and that
switch. So if the point you are testing and the previous
point tested are in different physical areas of the game,
look for the intervening connector and check it too.
voltage registered is the same as the transformer's coil
voltage(30 volts in this example), or very close to it, you
have no (or very little) voltage drop and your circuit is
probably operating properly. If, however, you get a
(HINT: You can perform a Zero Ohms Test on a single
lower voltage across the coil unwanted resistance is
component (switch, connector, etc.) by connecting
present somewhere in the circuit.
your two meter leads directly to the terminals of that
component. This is a good way to check if you have
properly fixed a fault in a component.)
VOLTAGE DROP
The presence of unwanted resistance will produce
an effect on a circuit known as voltage drop. Ohm's
Law can also be stated by the formula "E equals I x R."
This means that the voltage (E) across any circuit
element have a resistance (R) is equal to the current (I)
multiplied by the resistance. If, in our example in Figure
4, all of the circuit elements (fuse and switches) had
Zero resistance then the voltage drop across all of
them would be Zero since the current (I) would be
multiplied by Zero, thus producing a Zero voltage drop.
This means that in a properly operating circuit, all (or
almost all, remember some resistance is normal) of the
supply voltage will appear across the load enabling the
load to operate as it was designed to do.
If, on the other hand, any or all of these components
have unwanted resistance (denoted by the small "r" in
the boxes in Figure 4) they will produce a corre
sponding voltage drop, "e(4)," across it, equal to the
current, "I," multiplied by "r(4)." The same idea would
hold true for any of the other circuit elements by
multiplying their "r" by "I" to get their respective
To isolate the circuit component causing the resis
tance you would then proceed by moving your one
meter lead (the one on point "f") back in the circuit, one
point at a time ("d," then "c," etc.), until a point is
reached where full voltage is obtained. When this point
is found you have isolated the problem to the circuit
element you have just eliminated, just as in the case of
the Zero Ohms Test previously described. Don't forget,
however, that an intervening 'quick disconnect' con
nector could also be the culprit. The next step would be
to correct the problem and retest the entire circuit in
case more than one problem existed.
(IMPORTANT NOTE: While performing this test all
normally open switches (only the rollover switch in this
example) must be held closed. If not, an open circuit
would exist, and the full voltage would appear at all
points in back of the open circuit, because no current
will be flowing in the circuit and therefore would have
no (or little) voltage drop, even though a component
had a fairly high unwanted resistance. This same
condition can occur if a normally closed switch has a
very high resistance or is completely open.)
COMMON POWER CIRCUITS
Mention has been made several times in this and
previous articles of common power circuits, which feed
voltage drops ("e").
more than one circuit in a game. An example of such a
The result of all of this would be that the voltage
appearing across the load("E(L)" in Figure 4) would be
the source voltage, "E(S)," MINUS the sum of all the
individual voltage drops of the circuit components
("e(1)" plus "e(2)" plus "e(3)" plus "e(4)"). Thus, the
larger the voltage drops (produced by larger, unwanted
resistances) the less voltage will be supplied to the
circuit could be that part of the circuit of Figure 4
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between the upper side of the transformer winding and
point "d" (including the fuse and the normally closed
contacts of the "Tilt" and "Game Over" relays). You will
notice that I have indicated a line, labeled "A," which
represents the common point where other circuits fed
by this common circuit would be connected. We shall
now consider, using Ohm's Law, the effects on the
game of malfunctions in this type of common circuit.
If (in addition to the rollover switch and 10 Point
Relay circuit shown) other circuits were attached to
point "A" (in order to obtain power) each of these
for another test to determine the presence of unwanted
resistance in a circuit, the Voltage Drop Test. This test
circuits would use a certain amount of current to
is similar to the Zero Ohms Test, except it is performed
Continued on page 49
COIN
SLOT
© 46
The —THE
International
Arcade
Museum
August 1982
http://www.arcade-museum.com/

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