![background image](http://html1.mh-extra.com/html/viewsonic/va912-4/va912-4_service-manual_1020986026.webp)
Monitor Range Limits:
Min Vertical Freq - 50 Hz
Max Vertical Freq - 85 Hz
Min Horiz. Freq - 30 KHz
Max Horiz. Freq - 82 KHz
Pixel Clock - 140 MHz
Secondary GTF - Not Supported
______________________________________________________________________
(108-125) Detailed Timing / Descriptor Block 4:
Monitor Name:
VA912-4SERIES
(126) No Extension EDID Block(s)
(127) CheckSum OK
6. THEORY OF OPERATION
This section describes the function of the LCD monitor per functional block.
This monitor includes MB board, power/inverter board and button board.
6.1 MB BOARD
The MB board is a two-layer, single-landed. 5V and 12V DC power from the power adapter enters the board
through connector CN1. Other connectors on the board are for audio and button board .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
4 functional areas: flat panel controller, flash ROM, power regulator and Audio amplifier
6.1.1
Flat panel controller… RTD2523 (U6)
The heart of the system board is the scalar chip of RTD2523. The RTD2523 is a high performance, dual input
graphics processing IC for LCD monitors with resolutions up to SXGA. It provides all key IC functions required
for LCD panel. On-chip functions include an 8-bit triple ADC, PLL, DVI receiver, high scaling engine, OSD
controller and dual LVDS transmitter.
a)
Clock Generation:
Crystal Input Clock (XIN and XOUT): This is the input pair to an internal crystal oscillator and
corresponding logic. A 24.576 MHz crystal is recommended.
b)
Hardware Reset (Pin 56):
Hardware Reset signal is provided to MCU (I1). It is active high.
c)
Analog to Digital Converter:
The RTD2523 chip has three ADC's (analog-to-digital converters), one for each color (red, green and
blue) .The analog RGB and synchronous signals are connected to RTD2523 as described below:
Pin Name
Pin Number
Red +
37
Red -
38
Green +
34
23
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