Coin Slot Magazine - #090 - 1982 - August [International Arcade Museum]
MORE CIRCUIT THEORY
age and "R(L)" indicates resistance of the load.)
n the first part of this series the basic elec
trical circuit was defined. It was said to be a
"series" circuit, in that electric current would
flow from a power source, through a switch
(either simple or complex, as we discussed last month)
if it were closed, and finally through a load that would
perform some function. All these components have
been described in great detail in the past several
months. It is now time to tie them all together in an
actual circuit and discuss the basic electrical laws that
govern the operation of any such circuit
Figure 4 represents a simple game circuit, in which a
rollover switch (normally open) is used to energize a
relay (10 Point Relay) in order to
score 10 points. A portion of the
common switches (the normally
closed "Game Over" and "Tilt"
relay switches), which control the
application of power to some of
the game's circuits, are also shown
as well as the fuse in the coil
power line. All of these circuit
elements are shown, because in
order for electric current to get
to the load (relay coil) it must
pass through each of them.
Disregarding for the moment
the notations in Figure4 enclosed
in boxes, you will notice that the
coil power secondary of the
game's transformer is shown. It
is indicated that this produces a
voltage of 30 volts, which I have
labelled"E(S)"(more on notation
shortly). A circular arrow is also
shown, labelled"!," indicating the
flow of electric current through
the entire "series" circuit (from
transformer through the fuse,
switches and load, and back to
the transformer). Finally, you will
notice the notation "R(L)" nextto
the relay coil, which indicates
the resistance of the coil to the
flow of current. It should be noted
____»_
increase in resistance in one circuit can cause a
decrease in voltage in another circuit fed by it.
In a properly operating circuit, the current flowing
will be determined only by the source voltage and the
load's resistance (or impedance in the case of AC.
circuits, see note below). In the example in Figure 4
this would be the case if there
PINBALL
TROUBLE
SHOOTING
PART 6
BASIC CIRCUITS
CONTINUED
BY
RUSS
JENSEN
any of the circuit elements (fuse,
switches, etc) in the current path
between the transformer and the
load.
(NOTE: I have been using the
term resistance generically to
mean the resistance to the flow
of current. Actually the resistance,
as defined in Physics and Engi
neering, refers to the property of
circuit
elements that resists
equally both D.C. (direct current)
and A.C. (alternating current).
Certain circuit elements (in the
case of games, coils and motors)
have an additional resistance to
the flow of A.C. only, which is due
to their electromagnetic proper
ties and is known as reactance.
The
Russ Jensen concludes his explana
tion of the electrical circuits and how
they work that was begun in the July
issue of The Coin Slot. These principles,
when understood, will be of great value
to a collector trying to diagnose mal
functions in a pinball game.
closed.
There is a fundamental law of electrical circuit theory,
known as Ohm's Law, that can be represented by the
formula I equals E/R. This says that the amount of
current ("I") flowing in any circuit is equal to the voltage
("E") of the source divided by the resistance ("R") to
current flow in the circuit. This law will be the basis for
all the discussion to follow.
(NOTE: The notations "I," "E," and "R" (used for
current, voltage and resistance respectively) may seem
strange but are traditional in Physics and Engineering.
I have added (in parenthesis) additional modifiers to
provide information about the quantities during this
discussion. For example: "E(S)" indicates source volt-
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44 —THE COIN SLOT
in the resistance of that circuit to current flow. Of these
two factors the latter is the most common in malfunc
tioning games. However, as will be pointed out later, an
was no resistance presented by
that no current will flow until the
normally open rollover switch is
© The International Arcade Museum
The Ohm's Law formula is presented here to illustrate
the fact that two conditions can cause a decrease in
the amount of current flowing in a circuit; a decrease in
voltage supplying current to the circuit, or an increase
sum
of
these
two
resis-
tances(resistance and reactance)
is called impedance. This imped
ance would be used in theOhm's
Lawformula for coils and motors
in A.C. circuits only, in place of
"R(L)," and would be labelled"Z(L)"
to differentiate it from other true
resistances in the circuit.
If any of the circuit elements
(other than the load, of course)
have resistance, this will add to
the resistance of the circuit and
thus decrease the current flowing,since in the Ohm's
Law formula you are dividing the source voltage by a
bigger"R" resulting in a smaller"!." If all these circuit
elements (fuse, swtiches, etc.) are operating correctly
they will have Zero (or close to it) resistance. If,
however, any of them are causing problems they can
have some resistance, which I have denoted in Figure
4 by the small letters "r" (for example "r(l)").
The most common cause of unwanted resistance in
game circuits is dirty or misadjusted switch contacts
described in a previous article. A faulty switch can
exhibit almost any resistance up to, of course, an open
circuit(infinite resistance). The possible resistances of
the three switches shown in Figure 4 are indicated as
August 1982
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