Star Tech Journal

17
STAR*TECH JOURNAL/NOVEMBER 1982
TROUBLESHOOTING
GO'l'l't ,TEB
DISPLAYS
The physical appearance of a game can really
make or break a game. The player appeal will
be greatly enhanced by an attractive lightbox,
playfield and displays. Defective displays can
throw off the balance of the image that a
prospective player gets from a game. Playing a
game with defective displays can really frustrate
and confuse a player. Naturally, that player
will probably not return to challenge the game.
The 7-digit display filament offset voltage
is +8vdc generated by the+ 12vdc input to the
A2 power supply board by zener diode CR?
and RIO. The 4-digit display filament offset
voltage is + 5vdc, which is the same as the logic
supply voltage. The +8vdc is applied to the
center tap of the 5vac winding on the small
transformer. The +5vdc is applied to the
center tap of the 3vac winding on the small
transformer. The two pairs of AC offset voltages
then go up to the displays in the lightbox via
connector Al2J4.
The filament, which acts as a direct heated
cathode, works on AC power. The constant
variation of the AC voltage provides uniform
brightness across the face of the display and
also assures that the filament wire will not get
overheated and break or wear at any point. To
cut off the flow of electrons to the grid and
anode, a negative voltage (in reference to the
filament) must be applied to the grid or anode.
Since the filament AC voltage swings negative
every half-cycle, just grounding the grid would
still allow electrons to flow every half-cycle.
For this reason, a low +DC voltage is applied
to the filament in addition to the AC voltage.
On the negative half-cycle the filament will still
have a positive potential above the grounded
grid or anode. This is the purpose of the offset
voltages for the displays.
Following is a brief theory of operation of
the displays, along with troubleshooting infor-
mation. Presenting the knowledge and theory
first will allow you to more fully understand the
troubleshooting and problem solving aspect of
displays. The better understanding you have of
troubleshooting procedures, the less that game
will be down and the better the earning potential.
The theory of operation (see Figure I) of a
fluorescent digit display tube is similar to the
vacuum tube theory. The filament acts as the
cathode. When the filament is charged with
electricity and heated, electrons are emitted. If
a more positive voltage is applied to the anode
and grid at this time, electrons emitted from the
filament are drawn into the anode through the
grid. These electrons striking the anode will
excite the fluorescent substance on the anode
and emit light. If the anode and grid voltages
are dropped to zero or negative, no electrons
will be drawn to the anode and no light will be
emitted.
The configuration of Gottlieb's display
signal wiring is as follows:
.. ,
.,
A
Segments:
There are six separate voltages that should
be checked when you are troubleshooting dis-
plays. The voltages are generated with a
combination of the bottom board and A2
power supply board. The anode voltages are
regulated + DC supplied from the power supply
board. The high voltage section of the A2
board has a 60vac input that is rectified and
regulated by the QI and Q2 circuitry to
produce +60vdc. The zener diode CR6 provides
the +42vdc output from the +60vdc. The
+60vdc output is the high voltage supply for
the 4-digit status display.
B
C
Digits:
""" 111,11,
1 st and 2nd player
3rd and 4th player
Status ( and Bonus
if present)
D1 through D6 and D16 1 st and 3rd player
(and Bonus if
present)
D7 through D12 and D13 2nd and 4th player
D13 through D16
Status
Continued on Next Page
SEVEN DIGIT
DISPLAY
POWER
SUPPLY
A2
FOUR DIGIT
DIS PLAY
J1
J1
_+&DVDC
+ 42VOC
JJ
J1
----------1
IOEI
IDLTAIH
BOTTOM BOARD
'
'
m
1
VAC
:
L ______________________________ J
FILAMENT
OFFSET
Vdp
DIIIT
FDUII
DIIIT
5vac
3vac
Bvdc
60vdc
5vdc
42vdc
FILAMENT
,,._~----i-~
OFFSET
FILAMENT
VOLTAGE
VOLTAGE
0
c
0
0
0
d
e I
SEGMENT OATA
0
0
g
h
FIGURE 1