15
STAR*TECH JOURNAL/JULY 1982
COLOR CIRCUITS
The color circuits are pretty straightforward. The signals go into
the interface section where some amplification and impedance
matching occurs. These circuits are pretty sparse and simple.
Each color just has two transistors and a diode with some
resistors and capacitors. From here, the AC color signal is sent
by wires to the neck board.
The color output circuits are on the neck board. The color
signals going to the transistors are controlled by two variable
resistors called drive controls. There are only two, one for the red
and one for the green. The blue doesn't have one. In the emitter
part of each transistor is another variable resistor that is the cut
off control. These controls vary the amount of amplified AC
signal that goes to the cathodes of the picture tube. The more
signal, the more color. The bases of each of these transistors are
connected together are all connected to the blanking and beam
limiting transistors which are in the interface section.
The beam limiter helps control the brightness level, and the
blanking transistor rapidly turns the picture tube on and off so
that retrace lines don't show up on the screen. By turning up the
brightness on a good monitor, these four to six retrace lines can
be seen slanting diagonally across the picture.
PROTECTION CIRCUIT
To protect the high voltage section against voltages that are too
high coming from the power supply which could cause X-rays to
be emitted from the "flyback", a circuit senses the higher power
supply voltage, and using a transistor, turns off the horizontal
oscillator. Since the horizontal oscillator doesn't work, the
horizontal output transistor has nothing to feed the "flyback"
which in tum has nothing to feed the picture tube. The monitor
will be silent, have no picture, and will appear to be off. BUT
DON'T BE FOOLED. There is still that excessive amount of
voltage coming from the power supply. To find out, check the
emitteron TR502 of the Wells-Gardner monitors; or the emitter
of X04 for the Electrohome monitor. Here are the voltages you
should receive:
Wells-Gardner= 127VDC
Electrohome = 120VDC
The best place to measure this voltage on an Electrohome
monitor is at a pin marked Bl on the chassis. This is because a
13-inch color Electrohome monitor, the G07-FB0 or G07-902,
has an integrated circuit and very little else in the power supply.
Still, there should be 120VDC at Bl.
THE PICTURE TUBE (OR CRT)
The picture tube or CRT is an output device. In other words, the
end result of the circuits' work is displayed by this part. Actually,
the output of other circuits is in the neck of the picture tube.
First, there is the heater. The heater boils off electrons from
the cathodes so that they ( the electrons) shoot up to the screen to
excite the phosphors so that the three phosphors emit three
colors of light.
The cathodes are next, and again they emit electrons to tum
on the tube phosphors, making it glow. The cathode can arc or
short to the heater resulting in no picture and a defective picture
tube.
Next come the grids. The first grid is grounded. The following
grid is the screen grid which receives about 300VDC depending
on the brightness setting. The next grid closest to the picture tube
screen is the focus grid which gets about one fifth the amount of
voltage that is applied to the picture tube anode.
After jetting from the cathode through all these grids, the
electrons speed through a mask, a sheet of material with tiny
holes, and then excite the tiny dots of phosphor in the inside
surface of the picture tube screen. The green electron gun ( or
cathode and circuitry) spits out electrons which head for the
green phosphors only. The same goes for the red and blue guns.
The way the phosphor light blends determines the color seen.
Should these electron beams become too intense, they may bum
the phosphor. With the monitor off, this can be seen as a dark
permanent image of the video information on the tube screen.
ATARI
"DIG-DUG" STATIC MOD
To eliminate any static related problems on "Dig-Dug",
perform the following modification:
Solder a 1 uf capacitor between pins 5 and 7 of the 74128
located in position A/B-3 on the main logic board.
WILLIAMS
"HYPERBALL" REV 4 PROGRAM/FUNCTION SETTINGS
New "Hyperball" Program Available
Williams has released a revision 4 program for their "Hyperball"
game intended to alleviate some of the minor problems encountered
with this innovative game.
Among the improvements incorporated into the new three
ROM program set are:
The alphanumeric display will no longer repeat the same
message continuously or speed up to the point that it can
hardly be read.
While in a relatively high score situation, the ball shooter
would slow down noticeably and handicap the player. This
problem has now been corrected.
"Hyperball" games experiencing these symptoms should be
refitted with this newly available revision 4 program. Contact
your distributor for further information and exchange procedures.
"Hyperball" Manual Function Settings Reversed
The 'LIBERAL/CONSERVATIVE' game function settings
for Williams "Hyperball" are reversed in the game manual. The
adjustments should read:
Function Description
*
*
32
35
Reflex Wave Difficulty 00 (Liberal) to 09 (Conservative)
Bolt Feed Rate 00 (Liberal) to 09 (Conservative)
ATARI
"DIG-DUG" CUSTOM CHIPS
00 Video RAM Addresser
Allows RAM to be addressed by CPU and sync chain. Requires
CPU address bus to be tri-state during 2H high.
02 Universal Shift Register
Can be set up for 4 4-bit parallel to serial converters or 2 8-bit
parallel to serial converters. All registers use 1 set of control
signals. Can shift either direction.
04 Motion Object Controller
Generates the strobes and RAM addresses for the motion
objects. (MOC 24 style)
06 Custom 50 Controller
Interfaces between CPU and Custom 50s (Custom 4 bit micro-
processors). Commands and data are transferred via the data
bus. CID selects command or data. Part of the custom 50 data
bus is address and part is data (apparently).
07 SYNC Generator
Takes 6 MHZ and generates all horizontal and vertical timing
signals. More than 1 can be used in a system using HRESET and
VRESET.
51 Coin 1/0 Controller
This custom microprocessor handles 1/0 (R/W).
53 Steering Controller
This custom microprocessor handles inputs (for "Dig-Dug"). It
also can apparently scan keyboards and handles steering
controls. 8 different modes.