Service manual

Wells-Garnder Color Vector Monitor Guide
Page 58 of 73
DC (about 35V). Capacitors C100 and C101 form the first stage of filtering. Resistors R102 and
R103 and capacitors C102 and C103 form two low-pass filters which help filter out AC ripple.
Transistors Q100 through Q103 form and active filter that provides the stable, filtered DC
voltages.
The degaussing coil operates when power is first applied to the display, when the PTP(positive
temperature coefficient) thermistor is cool. Diodes D106 and D107 form a protective barrier
from any residual current that might enter the degaussing coil during normal game play. The
output voltages from the low voltage power supply should be as follows:
J101-2 ground
J101-3 +25 volts
J101-4 -25 volts
The picture tube filament voltage is taken from the front end of the low-voltage power supply
through D108 and R107.
X AND Y AMPLIFIERS
Both the X and Y amps are nearly identical. Only the Y amp is described.
The Y deflection signal from the game board is applied to the base circuit of transistor Q600.
Transistors Q600 and Q601 form a differential amplifier. Transistor Q602 is a constant current
source providing current to the differential amplifier. Transistor Q603 is the driver transistor that
provides current to the emitter-follower transistors Q605 and Q606. Transistor Q604 is a
constant current source that provides current to the driver transistor Q603. Fuse F600 can open in
case of circuit failure, protecting the deflection coil in the yoke from damage.
Z AMPLIFIERS
Since the red, green and blue amplifiers are identical, only the blue amplifier will be described.
Transistor Q502 is a common emitter amplifier used to provide gain for the blue intensity signal.
Resistor R509 is the blue drive pot, which determines the amount of gain in the blue amplifier.
Resistor R513 is the blue bias pot, which determines the cut-off characteristics of the blue
amplifier. The output of the Z amplifiers bias the cathodes of the three electron guns within the
picture tube.
Transistor Q503 is biased by a voltage from the spot killer. When transistor Q503 is cut off, the
collector of Q503 rises to the zener voltage of ZD500 (+4.3V). This allows the emitter of
transistor Q502 to rise in voltage, which disables the color signals to the picture tube.