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CT 9000 ® ADV
MAIN CONSOLE BOARD
3-30
The main console board consists of the following major compo-
nents, each of which will be discussed in greater detail in the fol-
lowing sections:
+ Power Supplies
+ Keyboard Interface
+ Speaker Control
* CPU
* Display Controller
Power Supplies
There are four power supplies on the main console board: +5V,
+12V, -15V and 1000VAC.
With the exception of a small filter inductor, L3, added to the input
of the regulators, the +5V and +12V supplies are identical to the
+5V and +12V supplies on the MOTHERBOARD.
Refer to the
MOTHERBOARD theory of operation for a complete discussion of
these circuits. +12V is used to power the speaker and the inverter
used to generate the voltage for the cold cathode fluorescent tubes
used to backlight the liguid crystal display. This inverter is not used
on the EL versions of console (PCB P/N 800877). The +5V is used
to power all remaining circuitry on the main console board.
inverter INV-1 is used to convert +12V to the 1000VAC needed for
the cold cathode fluorescent tubes used to backlight the display.
The inverter is turned on and off by the CPU.
A high signal placed
on U26 pint is inverted twice by U26 and turns on FET A1. This
provides a ground path for the primary side of the inverter. A low
signal on U26 pin11 turns the inverter off by opening the primary
side ground path.
Switching regulator U23 is configured as a buck regulator to gener-
ate an adjustable negative voltage supply. This supply is used to
control the viewing angle of the LCD.
The voltage can range from -
12V to -18V. Transistor Q4 is used to limit the top range of the
viewing angle voltage input. Transistor Q2 chops the input D.C.
voltage into a square wave.
This square wave is then converted
into a negative D.C. voltage by L4, D12 and C22.
Capacitor C10 is
used to set the switching frequency to 40 kHz.
Keyboard Interface
The eight keyboard switches are input to a buffer, U28, through
series resistors, R40-R47.
In addition each switch line is pulled up
to +5V by R32-R39, and is prevented from exceeding +5V by
diodes D3-D10.
The output of the buffer is input to eight TPU
channels of U22 (MC68332).
800961-C
Nov.
2000
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