GE MAC 1200 Service Manual page 31

LCD Power Supply
Adjusting Contrast
Backlight
Revision D
Functional Description: PCB Control CS_CI
The LCD power supply VEE of –23 V is generated from the +5 V logic supply. The
generation starts after HRESET_ becomes inactive to ensure that the logic supply of
+5 V first is applied to the display.
Contrast adjustment of the display is accomplished with the contrast voltage V0.
The level of V0 is controlled with the PWM signal BLCD_CONTR from the timer
module of the MPC855T. In addition, the contrast voltage is temperature
compensated.
The LCD backlight converter for the CCFL tube is located on the PCB Control
CS_CI too. The backlight converter is generated from the +5 V logic power supply.
The signal BLCD_ENBA switches the backlight on or off. The user can define the
backlight active time in the configuration menu.
MAC 1200 resting ECG analysis system
2012250-095
2-13