17
LCD Backlight Stage
The backlight is necessary for the LCD unit’s visibility or it will appear
almost black. The backlight circuit is powered by the BL Unreg line from
F003, but is switched by the LCD Backlight ON/OFF switch at the rear
panel to conserve battery power. The backlight switch works by inform-
ing IC404. IC404 sends a chip select pulse (XCS Panel D/A) accompa-
nied by serial data (HI SO) to EVR IC902. IC902 outputs a BL Level to
the backlight power supply to switch it ON or OFF. When the power
supply turns ON, 750Vp-p (92kHz) is applied to the fluorescent backlight
tube. To insure starting at low ambient light levels, a nearby LED is also
turned ON (not shown).
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