Service manual

ViewSonic Corporation Confidential - Do Not Copy VA702-3_VA702b-3
15
14.318 MHz crystal is recommended.
b) Analog to Digital Converter:
The MST8111A chip has three ADC's (analog-to-digital converters), one for each color (red, green and blue) .The analog
RGB signals are connected to MST8111A as described below
Pin Name Pin Number
Red + 63
Red - 62
Green + 60
Green - 59
Blue + 58
Blue - 57
c) OSD : The MST8111A has a fully programmable ,high-quality OSD controller. The on-chip static RAM(4096 words by 24 bits)
stores the cell map and the cell definitions.
d) MTV312 Micro controller: The MTV312 micro controller(MCU) serves as the system micro controller. It’s programs the
MST8111A and manages other devices in the system such as the keypad, the backlight, LED, audio and non-volatile RAM.
using general purpose input/output (GPIO) pins.
Pin number Pin Name Pin Number Usage
21 P1.3 Key / Power on ,off
13 P3.4 NV_RAM (U4) SDA
14 P3.5 NV_RAM (U4) SCL
25 P1.7 Key_down
9 P6.3 Key_right
24 P1.6 Key_up
16 P6.2 Key_left
37 P4.1 Key_mute
34 P5.6 VGA connector
23 P1.5 Key_select
42 P5.3 LED_red
41 P5.4 LED_green
32 P6.6 LCD panel power1 on / off control
3 P5.0 LCD panel power2 on / off control
36 P4.0 Backlight on / off control
e) Panel Power Sequencing ( VDDCTRL1, 2) ( Pin 32, 3) : The MTV312 has two dedicated outputs VDDCTRL1 and 2
( Pin32 and Pin3) to control LCD power sequencing once data and control signals are stable.
f) Panel interface (Pin 1~25, Pin75~128) : The MTV312 driver interface is highly programmable. It supports dual bus / dual port
for SXGA drivers.
6.1.2 Power Regulator MC34063A (U6),AIC1739 (Q4) : The MC34063A is a monolithic control IC containing the primary functions
required for DC to DC converters. The device consists of an internal temperature compensated reference, comparator, controlled
duty cycle.