cau ses ;1 low at pin 13, the start flip
flop IC7 l is cleared (reset) which
allows us to start the game by
pushing the start swit ch which puts
a logic 1 on pin 12 of the 7474 at C7 .
9. The signal 512 V (vertical)
occurs about every 17 milliseconds
( .017 seconds) . When it goes high
(no bubble), the high on pin 12 is
clocked through to pin 9. Note that
the signal, start, has no line over it
therefore it goes high to be true.
Therefore we have caused a start
COihl
Remember a line over a signal (Q)
means it is normally high and goes
low when true.
7 When the COi'"n is inserted, coin
(coin not) goes low. The low at A8
p1n 1 is inverted and A8 pin 2 (Q)
goes high . The low is now removed
from the set inputs of 87 and C7
which enables the flip flops to be
toggled with the D and C inputs.
3. If a static charge is introduced,
a small voltage is induced in the
antenna which goes directly to the
8. At the same time, the low
signal Qat 87 pin 4 forces pin 6 low.
The low is inverted and becomes a
high at C6 pin 12. The configuration
of C6 says output is low (bubble)
when either input is high (no
bubble) .
9. The resulting low at C6 pin 13
resets C7, the start flip flop, so the
game cannot be started.
If problems occur in starting a
game there are a couple of things to
check before doing any extensive
~nAY
swnn
condition.
10. When start goes high, start
(pin 8) goes low and resets the
attract flip flop. Remember, a low
on pin 1 causes a low on pin 5.
Therefore pin 6 of the 7474 goes
high which means attract (ATRC) is
in the reset or untrue state and the
player controls are active.
Now look at Figure 2 and we'll go
briefly through the circuit.
1. Note first tnat a signal called Q
goes to pin 4 of the 7474's at 87 and
C7. Pin 4 is the direct set input.
This means simply that a low
(bubble) forces the outputs of the
7474 to their active (true) states.
base of 01 .
4. A high on the base will cause
the transistor to conduct (closed
switch) and it becomes effectively a
short between collector and emitter.
Since the emitter is at ground, the
collector drops very close to
ground, or to a logic low.
5. This low turns off 02 (open
switch) which means that its col -
lector goes to a logic 1 .
6. A8 inverts the logic 1 and Q
goes low.
7. A low at C7 pin 4 forces pin 6
(ATRC) low so that signal is in the
active or true state . Therefore the
game is forced to the attract mode.
troubleshooting.
1. Make sure that the actuator
wire has not been inadvertently
bent. If bent down, the length of
time the switch is made will change
and although the coin counter might
trip, the game will not recognize a
valid quarter since the time may be
too short.
2. With a meter make sure that Q
is low and goes high as soon as the
coin switch is toggled.
An excellent description of the
above circuits may be found in the
Video Game Operator's Handbook.
This should be available through
your local A tari distributor.
Letter:
Gentlemen:
Update,Vol.2, No. 11, Oct. '76, pg.
Ar.\~N
fl
FIG., 2.
..,_-tt.
., .,
Cc5iiJ.
FQil efl PINI
3, col. 2, "1) A bubble indicates
logic low WVDC to 5VDC) "should
read "indicates a logic low (QVDC
to O.BVDC)."
Also, a distinction should be
made between static symbols ("0)
and dynamic symbols (HSYNCl.
Raymond J. Markiewicz ;:i
107 Mark Street ~
Latrobe, Pennsylvania •
~
1"!'1
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