Star Tech Journal

STAR*TECH Journal
September 7 992
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(2N4401) are very inexpensive
and again it is cheap insurance.
The switch matrix is a simple
circuit to work with. Ther•~ are
two IC's for output and two for
input. They usually don't fail but
may should some other voltage
within the machine come in con-
tact with a switch line.
The Cpu controlled lamps on
shuffle alleys have a habit of be-
coming intermittent. This is usu-
ally caused by the 27 ohm resis-
tors unsoldering themselves
from the Logic board due to ex-
treme heat. Watch those babies
when the machine is on, they will
take a layer or two of your skin off
if you should touch them!
The best fix I have found for them
is to replace them with 27 ohm 5
watt cement type resistors. They
are more suited for the job and
are not run near their operating
limits. Occasionally you will run
into a bad driver transistor in the
lamp circuits but this is not
nearly as common as the r,esis-
tors burning up.
Connectors on the driver board
are prone to the same barrel type
cracks as all the other boards are.
Along with this they will often
develop bad connections at the
interboard connection where the
driver plugs together with the
Cpu.
The best way to check this is to
hold the driver board up to a light
and look through the connectors,
if you see any pin that has a wide
space, replace the connector.
The Williams part number for
this connector is 5792-090661-00.
It is good to have plenty of these
on hand. They are often shot after
10 or 15 years of plugging and
unplugging. They cost a little
over a dollar a piece and it may be
worth changing all of them for
dependability.
The display driver looks rather
complicated at first but trouble-
shooting it is not as hard as it
looks. A good cleaning of all edge
connectors is always in order and
just the cleaning will solve many
of the intermittent problems.
Most older shuffles
used "old technol-
ogy" Roms that
run hot as a fire-
cracker.
If the problems go beyond this
they can usually be figured out
logically. Many outputs of the
display driver are shared by more
than one display glass. If you see
a digit or segment out in more
than one place you could usually
figure what area is causing the
problem by back tracking it on
the schematic. You will see what
displays have the same output
and usually be able to figure out
the bad IC or transistor from
that.
A common failure on the display
driver is one or more burnt l0K
ohm 1/2 watt resistors. This will
cause segments to be missing and
is generally caused by a bad dis-
play glass. You could unplug all
the glasses ( except for the one on
the driver itself, of course) and
often find a glass dragging down
the signal to other glasses. Plug
them in one by one (carefully!)
and if other displays begin to
show failure symptoms you could
bet that the glass you just
plugged in is no good. Replace it.
The Sound board is usually
trouble free but if trouble does
arise it could be traced down usu-
ally without too much difficulty.
If you get no sound, check the
fuses. The Sound board has its
own fuses separate from the main
power supply. They feed low volt~
age A/C to a bridge rectifier so
that the board will be supplied
with +12 and -12 volts. The +12
volts also feeds the input of a
standard three pin +5 volt regu-
lator to run the IC's.
A common failure on the older
sound board is the Rom. Most
older shuffles used "old technol-
ogy" Roms that run hot as a fire-
cracker.
The audio amp does go on occa-
sion but can be easily checked by
touching the wiper of the volume
control pot with your finger, if it
hums when you touch it, it is
probably fine.
The interface IC's are 4050
CMOS chips and they are not too
tolerant when it comes to surges~
and other spikes. A common
symptom of a bad interface IC
will show up usually as the sound
board making the wrong sounds.
Sometimes it will cause the board