STAR*TECH Journal
August 7992
power is interrupted in any way,
if it is not then there are probably
no bad connections.
Next, get out you digital multim-
eter again and set it to the NC
scale on a low voltage setting
(usually the 2 volt scale will do).
Now go back and measure the N
C voltage from the DIC outputs of
the power supply. Yes, I did say
the NC voltages!
Take those readings from the out-
puts to the ground terminal. If
you get any readings of over two
hundredths (.02 volt) on the +5
volts or two tenths (.2 volt) on
either the +12 or -5 then you are
probably looking at a bad power
supply.
REPLACING THE SUPPLY
Replacing the power supply is a
pretty straightforward thing to
do but I wish I had a nickel for
every time someone did it wrong,
I would enjoy alot of free lunches!
When replacing the power supply
you should do it one terminal at a
time. Do not pull off all the wires
together and then expect to re-
member where they all went.
Some games let you get away
with doing this because they use
normal color schemes for the
wires but many do not -so don't
get started with a bad habit.
It is usually easier to start with
the DIC outputs first because
many times the NC wires going
into the PIS are shorter and this
will make it a little "tighter"
when trying to juggle all this
around in the bottom of the cabi-
net.
Take your first terminal and
loosen it up and remove all the
wires from it. Note what terminal
you are working on because many
power supply connectors differ
from one another. One may have
the +5 at the top while others may
have + 12 or some other voltage
there.
Also note that there are two dif-
ferent grounds on the power sup-
ply, one is the NC ground and is
usually marked FG or chassis
ground, the other is the DIC
ground and is usually marked 0
(zero) volts, DIC Ground or sim-
ply Ground or GND. Make sure
you transfer to the proper ground
when switching wires.
Some power sup-
plies will generate
noise and this will
find its way into
the video.
Take all the wires from the termi-
nal and make sure they are
crimped properly or soldered to
their connector, if they are not, do
what you must to fix them or
replace them. Never wrap bare
wire around a screw terminal,
always use a connector. Continue
this procedure until all the wires
have been moved to the new
power supply.
When you are finished mount the
PIS to the cabinet and take a look
for the +5 voltage adjustment. If
it shows you which direction will
raise and lower the voltage, turn
it to a lower setting before power-
ing the game up. This will pre-
vent the board from being dam-
aged from possible overvoltage.
Sometimes PIS's come with the
voltage set a Ii tile on the high side
so make sure you lower it first!
Now tum the power to the ma-
chine on and take a measurement
from +5 volts to ground at the
Pcb. It will probably be a Ii ttle low
if you turned it down previously.
Now you must do a juggling act,
keep your meter leads on the logic
board and adjust the +5 volt ad-
justment on the supply until you
get about 5 to 5.1 volts. This
should be a safe figure for just
about any board.
WIERD NOISE
ON THE SCREEN
Some power supplies will gener-
ate noise and this will find its way
into the video. If you see slightly
dark stripes swirling around the
monitor it may be caused by the
PIS.
A simple and safe cure for this is
to make a filter which consists of
a 10 ohm 114 watt resistor, two
spade terminals and a piece of
heat shrink tubing.
Begin by crimping one spade ter-
minal to one end of the resistor.
Now slide the heat shrink tubing
over the entire resistor leaving
enough of the other end sticking
out so you could now crimp the
other spade terminal on to it.
Take this filter and attach one
end to the NC ground ( usually
marked as FG on the PIS) and the
other to the DIC ground. Your
noise should have disappeared
now.
Insteadofmakingupafilterwith
a resistor you could simply jump
the FG terminal to the DIC
ground terminal but the resistor
acts like a safety fuse should
wires get crossed in the future.