Troubleshooting guide

Cinematronics Vector Monitor Repair Guide v.1.0
Page 6 of 53
Analog Switch
From the DAC-80 the analog signal is then sent to a high-speed analog switch, ICl. The analog
switch has two parallel inputs for the display signal, and two controlling inputs, which select one of
two outputs from the switch.
The LF133310 analog switch at location IC1 is the most active component on the monitor. Both the
horizontal and vertical DAC output voltages pass through this switch and then become converted
into currents to deflect the beam to proper positions on the screen. The chip is mounted in a socket
for easy removal and should be a prime suspect for monitor that blows circuit breakers.
The switch passes the voltage output of the DACs through either of 2 channels: the lower channel
is for the initial position coordinate of a line segment, and the upper channel is for the final
coordinate. The CCPU controls the channels: initial position on pin 8 and line drawing (final
coordinate) on pin 1. If the upper channel in the switch is defective, say, in the horizontal section,
then there will be no horizontal lines on the display. The same is true for the vertical.
Output fifteen from the switch routes the analog signal through a 5K potentiometer (R102), a 10K
resistor, (R103) and to the input of the TL081 op-amp (IC102). The time constant developed by
these two resistors and the capacitor (C101) determine the length of the vector line seen on the
screen. Adjusting the potentiometer will adjust the length of the vertical lines seen on the screen.
Output ten from the analog switch routes the signal directly to the input of the TL081 op-amp, and
the resulting voltage across C101 determines the initial starting position of the vector. R130 is there
to protect the analog switch from any damage caused by the large inrush currents when charging
C101. The CCPU is responsible for waiting until C101 is fully charged to its initial voltage before
turning on the Z-axis.
ANALOG SWITCH CIRCUIT