Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 12 of 53
just R9 and R11 to ground, thus lowering the voltage at the anode of D4 even more because of the
lower resistance, than with normal intensity. Q2 is used as a switch to enable Q1 and Q3. Q2’s
purpose is to shut off the beam when the power is turned off. Q7 is a beam “on” delay to prevent
phosphor burns if someone was to unplug and plug in the machine rapidly. With Q1 and Q3 both
off, or Q2 off, current has no path to ground and the wiper voltage will be +90 volts regardless of
the brightness pot setting.
For a NORMAL INTENSITY vector, pin 3 of IC7 pulses low. Pin 4 then pulses high to +2.75
volts, turning on Q3. Current flows through R11, R9, R10 and through Q3 to ground via Q2. This
drops the voltage at the cathode to about +40 volts with the brightness pot full clockwise.
For a HI INTENSITY vector, pin 1 of IC7 pulses low. Output pin 2 pulses high to 2.75 volts,
turning on Q1. Current flows through R11, R9, through Q1 and to ground via Q2. This drops the
cathode level to about +20 volts with the brightness pot full clockwise.
The yellow wire to the cathode should show a +90 volt DC base with negative going pulses that
vary as the brightness pot it turned. For a no display condition, suspect IC7. The 7406 chip is an
open collector inverter and must have a pull-up resistor on its output. Verify that 4 to 5 volts is
always present at the junction of R1 and R2. This voltage is supplied by Q8, which is in an R/C
delay circuit to allow all voltages to settle on power up before a picture is displayed.
Q2 is designed to open the intensity circuit immediately after power is removed from the game.
This prevents the +90 volt blanking voltage from bleeding off before the high voltage bleeds off,
thus preventing a spot becoming burned on the CRT screen when the game is unplugged. Q2 is
kept on continually by a full wave rectified, unfiltered signal from the power supply through fuse
F1 (0.5 amp). For a no display condition, eliminate Q2 as a source of trouble by jumpering it
collector to emitter, being careful to remove the short before powering down the monitor, since this
short does eliminate the power down spot killer.
INTENSITY CIRCUIT