9600 Service Manual - gmecorp-usa.com

12 Video Control
CONTRAST AND BRIGHTNESS CONTROL
Brightness and contrast adjustment is provided to allow the service technician to set up
the monitor brightness and contrast. The brightness and contrast of the Fast Scan
monitors are controlled by the left and right contrast and brightness pots located behind
the top cover of the Workstation as shown in Figure 1. Brightness and contrast pots R2
and R1 from the left monitor, and R4 and R3 from the right monitor, are supplied with +5
volts on one side and DC common on the other. The control voltage is obtained from
the wiper on each pot. The control voltage is sent to the High Scan Brightness /
Contrast Control PCB where it is summed with portions of the voltage from the ambient
room light sensor. The resultant voltage is applied to pins 3, 5, 10, and 12 of U2 on the
High Scan Brightness / Contrast Control PCB, where it is amplified. The brightness and
controls drive voltages exit the High Scan Brightness / Contrast Control PCB at
connector P4 and goes to the monitors.
AMBIENT ROOM LIGHT CONTROL
Ambient Room Light Control is provided to adjust the brightness and contrast of the
monitors as lighting conditions vary. Ambient Room Light Control is obtained from the
IR Receiver PCB that is located between the two monitors at the top of the front bezel of
the Workstation. The sensor consists of a photocell which provides a variable
resistance, depending on the light level entering the sensor through the clear plastic
window in the bezel. The sensor is supplied with +12 volts, the output voltage of the
photocell is applied to resistor network R13 and R11 on the High Scan Brightness /
Contrast Control PCB. The voltage from the photo cell can be monitored at TP1. The
photo cell voltage is summed with the voltage from the contrast and brightness pots R2
and R1 from the left monitor and R4 and R3 from the right monitor.