Star Tech Journal

(
STAR*TECH Journal
)
June 1988
6
Bally Midway 7533 DAC Failures
Arnie Aarstad
Bally Midway Service Dept.
Franklin Park, Illinois
SUBJECT
Premature failure of the 7533 DAC's on the
sound boards. During extensive research on
the sound board's Digital to Analog con-
verter circuit, we have discovered a transient
condition which may result in premature
failure of this part.
CAUSE
This condition is due to overstressed metali-
zation related to pin 1 on this chip. The
situation occurs on power-down when the
Vee begins to fall and reaches about 1.5
volts. At this time, the voltage on pin 1
exceeds Vee for a fraction of a second. The
DAC is not designed to withstand this con-
dition.
CURE
Remove the 4 7uF capacitor connected to pin
1 of this chip. This will eliminate the tran-
sient condition on the circuit, and testing
indicates that this removal has no negative
effect on the overall operation of the circuit.
To remove the correct capacitor use the following guide .
• · ·•.· •.• •. Board Series
Item
• i\084-91863
A084-91671
• A084-91671
A084-91779
A084-91855
A084-91864
1.
2.
3.
4.
5.
6.
Board Name
Remove Capacitor
Sounds Good (Video)
Cheap Squeak Deluxe (Video)
• Artificial Artist (Video)
Turbo Cheap Squeak (Video)
T.C.S. Pinball (Pinball)
Sounds Deluxe (Pinball)
Cl22
Cl22
Cl22
Cl2
C30
Cl2
The following games use one or more of the sound boards identified by their item numbers:
Pinballs
Black Belt (5.)
City Slicker (5.)
Dungeons & Dragons (6.)
Escape from the Lost World (6.)
Hardbody (5.)
Heavy Metal (6.)
Motordome (5.)
Party Animal (6.)
Special Force (6.)
Strange Science (5.)
Videos
Demo Derby (4.)
Max R.P.M. (4.)
Power Drive ( 1.)
Rampage (1.)
Sarge (4.)
Spy Hunter (2.)
Spy Hunter II (l.& 4.)
Star Guards (1.)
Xenophobe (1.)
Zwackery (3.)