S*TJ JANUARY 1982 8
Operators!
Mechanics!
Are you searching for a
painless way to upgrade
your ability to repair the
Electronic games you
operate ... the games you
depend on for your
livelihood?
Randy Fromm's Arcade
Schools offers 46 hours
of comprehensive, practi-
cal training in electronic
amusement repair for
mechanics and operators.
You don't need an
oscilloscope ... to be
successful at repairing
Solid-State games. The
course stresses the
efficient use of test
equipment like the Logic
Probe
and
Digital
Multimeter; relatively in-
expensive equipment that
operators and mechanics
can easily afford.
Is the course expensive?
Not really. The tuition fee
of $400.00 includes over
$75.00 worth of textbooks,
databooks, and other
materials.
Randy Fromm's Arcade
School will not teach you
how to repair a jukebox,
electromechanical pinball
or vending machine. You
will learn about diodes,
transistors, power supplies,
electronic pinball, video
games (including a special
session on video games
that use the X-Y monitor
system), cross referencing
semiconductor replace-
ment parts, using a logic
probe, and more.
San Diego Arcade School
6123 El Cajon Blvd.
San Diego, CA 92115
714/286-0172
Dallas Arcade School
11857 Judd Ct.
Dallas, TX 75243
214/231-3307
CROWBAR PROTECTION
FOR
* WILLIAMS * "DEFENDER" * RAMS
BY DANIEL ZAVARO, S.F . MUSIC & GAMES, SAN FRANCISCO, CA
In recent months, I have repaired four "Defender"
video games which had serious damage to RAM
memory chips. In each case, ALL TWENTY-FOUR
RAM chips were destroyed!!! These 4116 memory
parts cost $5 to $6 each. I built a crowbar protection
circuit to protect the RAM. It consists of a 13 volt Zener
diode (SK3788) which triggers an SCR (SK3685)
rated at 8 amps. When the supply voltage exceeds 13
volts, the Zener diode begins to conduct, which turns on
the SCR. This quickly blows the 4 amp slo/blo fuse
(labeled F 3 ), thus removing all power from the RAM
chips. I built this circuit on a small square of perforated
board and installed it near the power supply. (See Fig.
1.)
A second method for RAM protection is simpler but
probably not as effective. Locate the 12 volt (regulated)
supply wire. It is pin 5 of Power Input connector 1J3.
Simply install a 0.6 amp slo/blo fuse in series with this
supply wire. The RAM chips normally consume about
0.5 amps. My guess is that the power supply voltage
slowly increases above 12 volts. This may be due to
temperature effects on the regulator chip (IC2, 723)
and/ or on the series
+12V
(FIG. 1)
P.S. o - - - - - - < - - - - - - - - e - - - , , +12V
pass transistor
RAM
SK3685
(Ql, 2N4075). If
100
so, the 0.6 amp fuse
will provide some protection
½W
for all those expensive RAMs. -=- -=-
EXIDY
"TARG" JOYSTICK* SUGGESTION
BY TODD ERICKSON, SUMMIT AMUSEMENT, ST. PAUL, MN
"Targ" is basically a good game that is getting very little
play. A simple physical examination of the joystick will
explain why. Many of the older games never had a
decent joystick. I installed a 4-way Wico on my "Targ"
and the income went up substantially. A few extra
dollars spent to modify this game will greatly increase
the profit.