Star Tech Journal

STAR*TECH JOURNAL/NOVEMBER 1982
6
BALLY/MIDWAY'S
VIDEO TROUBLESHOOTING GUIDE
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Find these hidden words in the
above puzzle:
LATCH
COUNTER
PROCESSOR
BUFFER
MULTIPLEXER
DRIVER
INVERTER
MEMORY
DECODER
REGISTER
MURPHY'S
LAW
#409
Inside every large problem
is a small problem struggling
to get out.
Introduction
The most common problems occur in harness
components such as the coin acceptor, player
controls, interconnecting wiring, etc. The TV
monitor and PCB computer cause their share of
problems too, but not as much as the harness and
its component parts. TV monitor troubleshooting
will not be covered here because it was covered in
S•TJ, Vol. 4, Nos. 4 and 5.
As you already know, the PCB computer is a
complex device with a number of different circuits.
Some circuits remain basically the same among
games, but overall there are a great many differences
between them. PCB troubleshooting procedures,
therefore, can be lengthy and will differ greatly
'llllonggames.
General Suggestions
The first step in any troubleshooting procedure is
correctly identifying the malfunction's symptoms.
This includes not only the circuits or features
malfunctioning, but also those still operational. A
carefully trained eye will pick up other clues as
well. For instance, a game in which the computer
functions fail completely just after money was
collected may have a quarter shorting the PCB
traces. Often, an experienced troubleshooter will
be able to spot the cause of the problem even
before opening the cabinet.
After all the clues are carefully considered, the
possible malfunctioning areas can be narrowed
down to one or two good suspects. Those areas can
be examined by a process of elimination until the
cause of the malfunction is discovered.
Harness Component Troubleshooting
Typical problems falling in this category are coin
and credit problems, power problems and failure of
individual features.
No Game Credit
For example, your prospective player inserts his
quarter and is not awarded a game. The first item
to check is if the quarter is returned. If the quarter
is returned, the malfunction most certainly lies in
the coin acceptor itself. First, use a set oftest coins
(both old and new) to ascertain that the player's
coin is not undersize or underweight. If your test
coins are also returned, coin acceptor servicing is
indicated. Generally, the cause of this particular
problem is a maladjusted magnet gate. Normally,
this will mean slightly closing the magnet gate a
little by turning the adjusting screw out a bit ( see
S•TJ, Vol. 4, No. 3 on coin door maintenance for
more details.)
If the quarter 1s not returned and there is no
game credit, the cause of the malfunction may be
in one of several areas. First try operating the coin
return button; if the coin is returned, the problem is
most likely in the magnet gate. Enlarge the gap
according to the coin acceptor service procedures.
If this does not cure the problem, remove the coin
acceptor, clean it and perform the major adjustment
procedure.
If the trapped coin is not returned when the
wiper lever is actuated, you may have an acceptor
jammed by a slug, gummed up with beer, a jammed
coin chute, or mechanical failure of the acceptor
mechanism. In this case, first check for the slug
that will generally be trapped against the magnet. If
so, simply remove the slug and test the acceptor. If
the chute is blocked, remove the acceptor and
remove the jammed coins. If there is actual failure
of the acceptor, remove the unit and repair as
indicated in the coin acceptor service procedures.
If the coin is making its way through the
acceptor (that is, falling into the coin box), yet
there is still no game credit, you either have a
mechanical failure of the coin switch or electrical
failure of the coin and credit circuits. The first
place to begin is by checking the coin switch. Most
of these switches are the make/break variety of
micro switch, which is checked by testing for
continuity between the NO, NC and C terminals.
When not actuated, the NC and C terminals
should be continuous and the ·No terminal open.
When operated, the NO and C terminals should
close and the NC should be open. If the coin switch
checks out, examine the connections to the terminals
to make sure there is good contact. If necessary,
use the continuity tester and check from the
terminal lug on the switch to the associated PCB
trace. This will tell you if there is a continuous line
all the way to the credit circuit. If the coin switch
wires check out, the problem is in the computer -
most likely in the coin and credit circuitry.
If you do get game credit when a coin is
deposited, but the game will not start when the
start switch is pressed, you may have a problem in
the start switch, the interconnecting wiring or in the
computer. First check the switch. If the switch is
OK, proceed to check the wiring. Again, make sure
you go from the terminal lug on the switch to the
PCB trace. This way, you will check the terminal
contact as well as PCB edge connector contact. If
the wiring is continuous, proceed to check the PCB
credit circuit. If not, check each section of the
wiring until the discontinuity is located. If the
wiring is OK, the problem must lie in the computer.
Transformer and Line Voltage Problems
Your machine must have the correct line voltage to
operate properly. If the line voltage drops too low,
a circuit in the computer will disable game credit.
The point at which the computer will fail to work
will vary some from game to game; but no game
will work on line voltage that drops below I 0Svac.
Low line voltage may have many causes. Line
voltage normally fluctuates a certain amount during
the day as the total usage varies. Peak usage times
occur mainly at dawn or dusk, so if your machine's
malfunction seems to be related to the time of day,
this may be a factor. A large load connected to the
same line as the game (such as a large air condi-
tioner or other device with an exceptionally large
motor) may drop the line voltage significantly •
when starting up. This drop can result in an
intermittent credit problem. In addition, poor
connections in the location wiring, plug, or line
cord may also cause a significant drop in power.
Cold solder joints in the game's harness, especially
in areas like the transformer connections, interlock
switch, or fuse block, may also produce the same
results, although probably on a more permanent
basis.
Continued on Next Page