Circuit Description - ViewSonic VS11661 Service Manual

4. Circuit Description

4.1 MAIN BOARD
The main board is a two-layer, single-landed design with ground and ground planes provided.
The VGA cable is a signal cable that contains video signal, sync signal and DDC signal from PC VGA adapter.
This system board consists of 3 functional areas: flat panel controller, Micro controller and audio controller.
4.1.1 Flat panel controller...NT68625F (U3)
The heart of the system board is NovaTek NT68625F. The NT68625F is a graphics processing IC for
LCD monitor. It provides all key IC control functions required for LCD panel. On-chip functions
include a high-speed triple-ADC, TMDS receiver, PLL, high scaling engine Micro processor and
OSD controller, manages other devices in the system such as the keypad, the backlight, LED and
audio general purpose input/output pins.
39
125
124
125
126
66
65
28
40
118
49
50
31
32
a) Clock Generation:
Crystal Input Clock (OSCI and OSCO). This is the input pair to an internal crystal oscillator and
Corresponding logic. A 12MHz crystal is recommended.
b) Hardware Reset (Pin 48)
Hardware Reset signal is generated by NT68625F (U3/Pin 48). It assert a reset signal at least
1ms.
c) Analog to Digital Converter
The NT68625F chip has three ADC's (analog-to-digital converters), one for each color (red, green and blue).
The analog RGB signals are connected to NT68625F as described below
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Pin number
PA6
AD1
PC5
PB0
PB0
PA0
PA2
PA3
PA7
PWMB
DDCD_SDA
DDCD_SCL
DDCA_SDA/RS232_TX
DDCA_SCL/RS232_RX
Pin Name
R+
R-
G+
G-
B+
B-
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Pin name
Key-Menu
Key-Sel/Auto
Key-Power on/off
Key-Right
Key-Left
LED-amber
LED-green
Backlight-adj.
SDA-VGA (Debug)
SCL-VGA (Debug)
SDA (Debug)
SDA (Debug)
Pin Number
24
25
22
23
19
20
29
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Pin function
VX2255wmh-4
VX2255wmb-4