Star Tech Journal
Issue: 1983-March - Vol 5 Issue 1 - Page 10
STAR*TECH JOURNAL/MARCH 1983
10
School For
Electronic
Games
TWO-WEEK COURSE
COVERS VIDEO AND
PINS. BY SCHEMATICS!
OUR 11th YEAR!
Calk
Coin
College
P.O. BOX 810
NICOMA PARK, OK
73066
405/789·534
TIRED OF WAITING
FOR YOUR BOARDS?
HOW MANY TIMES ARE YOU WILLING TO
HEAR, "YOUR BOARDS ARE NOT READY
YET'? MAKE THE CHANGE - COME SEE
US AND GET RESULTS - NOT EXCUSES!
"FLAT RATE"
prices for all repair and exchanges
on printed circuit boards:
In an effort to streamline the processing and speed up our
printed circuit board repair/exchange program, we have
established a "flat rate" price for all repair and exchanges
(Monitor PC Boards not included).
These rates will NOT apply: (1) If board has been
brutalized or damaged by the customer. Missing components
will be charged separately. (2) Two sets of boards in metal
cases.
"Flat rate" charges will apply in ALL other cases.
LOGIC, CPU, MPU ... $60
POWER SUPPLY ..... 41
SOLENOID ORIVER ... 41
SOUND/AUDIO ...... 41
ATARI AUXILIARY ... 70
SCORE DISPLAY ... $41
LAMP DRIVER ...... 32
TRANSFORMER ..... 34
ATARI VECTOR
GENERATOR ...... 70
Fastest Service ... Quantity Discounts ... Call Now!
FRISCO ELECTRONICS
& VENDING INC.
3299-19th Street San Francisco, CA 94103
(Authorized Atari Service Center)
OPEN 24 HOURS!
DAY: (415) 648-5466 NIGHT: (415)359-5641
SEGA ELECTRONICS'
ROM LINE (PART 6)
Starting with this installment of the ROM Line,
we'll look closely at the workings of integrated
circuits. We'll concentrate on those ICs
commonly used in almost any video game
computer. In troubleshooting a game logic
board, it is very important to have a working
knowledge of the elements of that board- the
ICs that compose the assorted circuits. If a
technician becomes familiar with all the inputs
and outputs of the I Cs he is troubleshooting, he
takes a big step in reducing repair time and
imporving his ability. So, let's start with the
basic IC circuits from which more complex I Cs
are made. Keep in mind that in digital elec-
tronics, we are concerned with 2 voltage levels;
one represents a high, or about +5 volts, the
other a low, or about O volts. These levels are
usually labeled" l" or" H" for high, and "0" or
"L" for low.
High and low levels can be formatted in two
ways - serial and parallel. The serial repre-
sentation is simply a single line, say an input to
an IC, that varies high and low. The parallel
format consists of many lines that contain
highs and lows. This format is commonly used
in computers as either the address or data bus
from the microprocessor. At any one time,
there is a pattern of highs and lows on all lines
of the address or data bus. Now, the basic IC
elements consist of gates, or logic circuits, that
produce one and only one output for a particular
set of inputs. The rules for determining what
output level will occur are set by the truth table
for each gate. The basic gates, then, are called
NOT, AND, NAND, OR, and NOR There
are only five; but we can combine them to form
more complex logic circuits. For now, here's
how the simplest gates work:
NOT- The schematic symbol is
This and the remaining gates have two inputs;
so, four possible combinations exist, as shown
in the truth table:
A
B
Q
0
0
1
1
0
1
0
1
0
0
0
1
The AND gate always produces the outputs
shown. If they are different from these, you'll
know that either the gate or its connecting
circuits are bad, or that you are looking at
another kind of gate. The common identifier for
the AND gate is 7408.
OR - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
0
1
1
1
Again, we have the same sets of inputs as the
AND gate, but as you see we have a unique set
of outputs for the OR gate. The common ID #
for this gate is 7432.
NAND - Schematic symbol:
A~Q
The input is labeled A, the output is Q. So, with
only one input, we have only two possible input
combinations to deal with, 1 or 0. If I is present
at A, the NOT circuit inverts the output, so a 0
appears at Q. 0 at the input produces a I at the
output. We can construct a truth table for the
NOT gate as follows:
(INPUT}
A
0
1
(OUTPUT}
a
1
0
The truth table tells us that the NOT gate
should always work this way; if you were
troubleshooting one that had a low input and a
low output, you would know immediately that
something is wrong. The gate itself, or some-
thing connected to it, could be bad. The truth
table for any IC, then, tells you what should
occur. When the IC acts differently from the
rules in its table, you know something is wrong
immediately. How's that for a handy piece of
test equipment? By the way, the common
numerical identifier for the NOT gate is 7404.
AND - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
1
1
1
0
See anything familiar? The NAND gate is
simply an AND gate with its outputs inverted.
The common ID# for this gate is 7400.
NOR - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
1
0
0
0
Continued on next page.
10
School For
Electronic
Games
TWO-WEEK COURSE
COVERS VIDEO AND
PINS. BY SCHEMATICS!
OUR 11th YEAR!
Calk
Coin
College
P.O. BOX 810
NICOMA PARK, OK
73066
405/789·534
TIRED OF WAITING
FOR YOUR BOARDS?
HOW MANY TIMES ARE YOU WILLING TO
HEAR, "YOUR BOARDS ARE NOT READY
YET'? MAKE THE CHANGE - COME SEE
US AND GET RESULTS - NOT EXCUSES!
"FLAT RATE"
prices for all repair and exchanges
on printed circuit boards:
In an effort to streamline the processing and speed up our
printed circuit board repair/exchange program, we have
established a "flat rate" price for all repair and exchanges
(Monitor PC Boards not included).
These rates will NOT apply: (1) If board has been
brutalized or damaged by the customer. Missing components
will be charged separately. (2) Two sets of boards in metal
cases.
"Flat rate" charges will apply in ALL other cases.
LOGIC, CPU, MPU ... $60
POWER SUPPLY ..... 41
SOLENOID ORIVER ... 41
SOUND/AUDIO ...... 41
ATARI AUXILIARY ... 70
SCORE DISPLAY ... $41
LAMP DRIVER ...... 32
TRANSFORMER ..... 34
ATARI VECTOR
GENERATOR ...... 70
Fastest Service ... Quantity Discounts ... Call Now!
FRISCO ELECTRONICS
& VENDING INC.
3299-19th Street San Francisco, CA 94103
(Authorized Atari Service Center)
OPEN 24 HOURS!
DAY: (415) 648-5466 NIGHT: (415)359-5641
SEGA ELECTRONICS'
ROM LINE (PART 6)
Starting with this installment of the ROM Line,
we'll look closely at the workings of integrated
circuits. We'll concentrate on those ICs
commonly used in almost any video game
computer. In troubleshooting a game logic
board, it is very important to have a working
knowledge of the elements of that board- the
ICs that compose the assorted circuits. If a
technician becomes familiar with all the inputs
and outputs of the I Cs he is troubleshooting, he
takes a big step in reducing repair time and
imporving his ability. So, let's start with the
basic IC circuits from which more complex I Cs
are made. Keep in mind that in digital elec-
tronics, we are concerned with 2 voltage levels;
one represents a high, or about +5 volts, the
other a low, or about O volts. These levels are
usually labeled" l" or" H" for high, and "0" or
"L" for low.
High and low levels can be formatted in two
ways - serial and parallel. The serial repre-
sentation is simply a single line, say an input to
an IC, that varies high and low. The parallel
format consists of many lines that contain
highs and lows. This format is commonly used
in computers as either the address or data bus
from the microprocessor. At any one time,
there is a pattern of highs and lows on all lines
of the address or data bus. Now, the basic IC
elements consist of gates, or logic circuits, that
produce one and only one output for a particular
set of inputs. The rules for determining what
output level will occur are set by the truth table
for each gate. The basic gates, then, are called
NOT, AND, NAND, OR, and NOR There
are only five; but we can combine them to form
more complex logic circuits. For now, here's
how the simplest gates work:
NOT- The schematic symbol is
This and the remaining gates have two inputs;
so, four possible combinations exist, as shown
in the truth table:
A
B
Q
0
0
1
1
0
1
0
1
0
0
0
1
The AND gate always produces the outputs
shown. If they are different from these, you'll
know that either the gate or its connecting
circuits are bad, or that you are looking at
another kind of gate. The common identifier for
the AND gate is 7408.
OR - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
0
1
1
1
Again, we have the same sets of inputs as the
AND gate, but as you see we have a unique set
of outputs for the OR gate. The common ID #
for this gate is 7432.
NAND - Schematic symbol:
A~Q
The input is labeled A, the output is Q. So, with
only one input, we have only two possible input
combinations to deal with, 1 or 0. If I is present
at A, the NOT circuit inverts the output, so a 0
appears at Q. 0 at the input produces a I at the
output. We can construct a truth table for the
NOT gate as follows:
(INPUT}
A
0
1
(OUTPUT}
a
1
0
The truth table tells us that the NOT gate
should always work this way; if you were
troubleshooting one that had a low input and a
low output, you would know immediately that
something is wrong. The gate itself, or some-
thing connected to it, could be bad. The truth
table for any IC, then, tells you what should
occur. When the IC acts differently from the
rules in its table, you know something is wrong
immediately. How's that for a handy piece of
test equipment? By the way, the common
numerical identifier for the NOT gate is 7404.
AND - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
1
1
1
0
See anything familiar? The NAND gate is
simply an AND gate with its outputs inverted.
The common ID# for this gate is 7400.
NOR - Schematic symbol:
Truth table:
A
B
a
0
0
1
1
0
1
0
1
1
0
0
0
Continued on next page.
Future scanning projects are planned by the International Arcade Museum Library (IAML).