STAR* TECH Journal
September 1992
Also, some early power supplies
have a -300 volts circuit installed
on them that was used in the first
two electronic pinballs from Wil-
liams, Lucky 7 and Hot Tips. You
often find shuffie alleys equipped
with this power supply even
though that section is not used.
Warning: That circuit although it
is not used is still active on the
power supply and can pack quite
a jolt if you lay your fingers across
the back of the board, especially if
the machine was just turned off.
Be very careful when handling
these powers supplies! The parts
that hold the voltage are C9 and
Cl0. Discharge them to be on the
safe side.
COMMON FAILURES
~he most common failure in
these Power Supplies is the dis-
play voltage. You will usually
lose one of the 100 volts supply
rails. This is commonly caused by
a bad or arcing display glass. In
general practice, I would check a
few parts out and judging from
their condition determine what
course to take.
You want to check the rectifier
diodes (D3 & D4). These rarely
goes but should be checked. Next
check the filter capacitors out.
They are the lOOufd at 150 or 160
volts. If they are reading bad or if
the ends of them seem swollen,
change them.
If you still don't have the problem
solved, troubleshoot the voltage
regulation section. You will usu-
l""""J.ly find the problem there. The -
l. 00 V is com prised of a mirror
circuit of the + 100 V rail. This
circuit is relatively easy to
troubleshoot.
One note, if one or two of the
semiconductors are blown you
should change 4 parts. For ex-
ample, if you find Q3 and Z4 bad
you should change them as well
as Q4 and Z3. In high voltage
circuits, many times a problem
won't show when reading parts
with a meter but when you put
the High Voltage to them they
will breakdown and this could
cause your new parts to go up in
smoke. Changing the four parts
together is "cheap insurance".
There are about a
50/50 mix of Cpu's
out there with
good and bad
those solid black ones. If you re-
move a Rom from the socket and
the socket is one solid piece not
allowing you to see the board be-
neath it then you have the bad
ones. These are usually so bad
that you could remove the Rom
with your fingers very easily. Re-
place them, they are garbage.
The other common failure on the
Cpu is the barrel cracked connec-
tors, follow the procedure above
for fixing that. Be careful around
Jack 1J3 (upper left), it is easy to
bridge the blanking line connec-
tion to ground at that point. This
will cause the game to have no
displays.
Always check your battery holder
and if need be replace it along
with a new set of alkaline batter-
ies. This will keep it running for
years to come.
sockets.
If you should get a failure in the
+5 volt circuit it is very simple to
fix. It is either a bad diode, bad
filter cap or a bad regulator.
Troubleshooting this section is
easy!
Any other voltage that originates
from this power supply for the
most part goes straight through.
The System 3 through 6 Cpu
board is dependable. The most
common failure is not electronic
but mechanical. The Rom sockets
(and possibly others) are usually
at fault.
There are about a 50/50 mix of
Cpu's out there with good and bad
sockets. The bad sockets are
The driver board is a source of
many of the problems you will
run into. These problems can in-
volve solenoids, lamps (Cpu con-
trolled) or switches.
In the solenoid sections you will
often run into transistor failures.
Troubleshooting this area is done
using standard techniques but
can get a little deeper when a bad
transistor takes out the pre-
driver and IC before it.
When replacing any IC's, it is
recommended that you first in-
stall a good quality socket. This
makes any future repairs alot
simpler. If an output transistor is
bad, it is also good practice to
change its associated pre-driver
just in case it took some damag-
ing current. The pre-drivers