Coin Slot

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
.com
m
:
u
se
u as
from little
m
d
any electronics store
for as e
$20. This is an
-
e
ad
o in ad game
l
c
essential tool
servicing.
When used as an
r
n
a
w. selectable functions) it measures
Ohmmeter
of
Dow (one
w its
w
/
/
:
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
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