Play Meter

By Joe Sill up
Remember the playfield
Solid State Pinball
Now that pinball machines are
almost totally solid state , the mecha-
nic in the game room has little to do
in the way of maintaining the
machines . Most problems with these
games can be solved by repair or
replacement of the various printed
circuit boards located inside the
game .
However, the most important
thing to fix first in a solid state
pin game is the playfield . Unlike
video games , which contain very
little other than a computer , TV
monitor , and several controls , pin-
games have coils and lamps and
switches under the playfield which
operate as a system to make the
game . A problem in any of these
areas will affect the operation of the
computer circuitry in the game , and
possibly result in circuitry damage .
We will discuss some of the problems
commonly encountered on playfields
that can lead one to think he has
"bad boards" when in reality the
playfield itself is at fault .
First , and most important , never
work on the playfield of a solid state
game with the power on . A
momentary short between a coil
terminal and a switch will send 40V
of solenoid voltage down a SV logic
line to the CPU board , very likely
causing circuitry damage to the CPU .
The same holds true for lamp sockets
and switches . So if you have to
change a coil or a light bulb , or adjust
a switch blade, always turn the game
off first .
Improper scoring is not always due
to a bad CPU board . For example ,
many games have target banks
located close to pop bumpers . The
switches under the target bank close
when the targets drop , and are
supposed to stay closed until the
bank resets. But if the switch contacts
are dirty or the switch blade tension is
improper, the force of the pop
bumpers operating will vibrate the
switches , opening and closing the
contacts momentarily. This causes
the CPU to score the value of the
drop target instead of the pop
bumper value . Also , if there are star
rollovers located close to pop
bumpers , the same thing may
happen. The forcE! of the pop
bumper operating may cause the
switch under the star rollover to
vibrate closed , thereby scoring an
improper value . The solution to both
of those problems is proper switch
blade tension adjustment .
Bally and Stern machines use
.OSMFD capacitors across stand-up
target , star rollover , and pop bumper
switches . The purpose of these
capacitors is to allow the CPU board
to "see" a closed switch faster than
would be possible without the
presence of the capacitor . Due to the
extreme vibrations involved in these
areas of the playfield , the leads of the
capacitors occasionally break . This
results in a "no score" situation if the
switch with the broken capacitor is
struck fast and hard by the ball . The
center target on Bally playfields is
famous for this problem . Replace-
ment of the broken capacitor with a
disc-type capacitor with thicker leads
will usually solve the breakage
problem . Capacitors of this type are
readily available at electronics shops
such as Radio Shack.
Playfield cleaner is an inadvertant
enemy of solid state pin games . If the
cleaner is applied too liberally , it will
run down between the blades of the
stand-up switches on the playfield ,
and soak into the bakelite spaces
between the switch blades . This can
cause the CPU to "see" either a
shorted switch or a switch that is
opening and closing r~pidly . The
result is either no score or too much
score from that switch . If this
happens you will have to disassemble
the swtichstack and clean the
spacers , which is a tedious job. So be
careful when you clean the playfield .
Broken wires can also be a cause
of improper scoring . If a lamp wire
comes into contact with a switch
terminal , it will cause the CPU to
"freak out" and score everything that
it can possibly score . The same holds
true for a coil wire that may be
shorting to the coil frame . When that
particular coil is activated, the
solenoid voltage may pass through
the frame into the switch blade, again
causing the CPU to "freak out" and
score improperly or shut down .
To solve these types of problems,