IBM 6656HG2 - T 560 - 15" LCD Monitor, Service Manual, Page: 12 / 34

DESCRIPTION OF BLOCK DIAGRAM
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1. Genesis Chip (Scaler chip)
GM5020 (U201) is one chip IC which it supports six function block of Video pre amp, PLL, A/D converter
OSD IC, TMDS receiver and scaler.
Video signal (0.7Vp.p) clamped through C204, 210, 211 inputs to U201. These R, G, and B analog signals
converted to 8bit digital signals through pre amp’s amplifying(1/0.7 time) to match AD converter’s operation
range from 0V to 1V and AD converter’s converting analog to 8 bit digital.
Internal PLL inputs horizontal sync signal and outputs clock to ADC and scaler for precise data catching.
Scaler inputs 8bit digital signals and clock, and carries out image processing that interpolates input signal
less than 1024*768 resolution to that of 1024*768 resolution, mixes OSD(On Screen Display) signal by
interfacing with internal OSD IC, and outputs clock, H/V sync, 24bit RGB data, and DE(data enable) signals
which Transmitter(U401) needs.
For supporting digital interface, this IC has internal TMDS receiver converting serial data signal to parallel.
And parallel signal almost similar as 24bit RGB data signal of AD converter’s output goes to scaler which
conducts same operation of analog interface flow that described before.
2. Panel-Link Circuit
Panel link transmitter (U401) delivers digital signal to the receiver inside LCD module by method of abstraction.
The abstracted signals are pairs of TX0+-, TX1+-, TX2+-, TXC+- of which voltage swing is 0.5V each.
Its swing is similar to LVDS (Low Voltage Differential Signal).
Transmitter (U401) gets signals of clock, H/V sync, 24bit RGB data, and DE(data enable) from U201, and outputs
TMDS (Transition Minimized Differential Signal) through TX pins.
When PD pin’s input is low, transmitter goes to power down mode.
3. System Controller (Microprocessor) Circuit
1) Microprocessor (U501) distinguishes polarity and frequency by calculating horizontal and vertical sync input
from signal source.
2) Microprocessor (U501) carries out power control by sending power-down trigger signal to U201, LCD module
and inverter for required power sequence and low power consumption.
3) Microprocessor (U501) communicates with EEPROM (U506), and GM5020 (U201) through IIC(2 lines) or
6 bit bus line. It makes all devices proper operating with communication channel.
4) Microprocessor (U4) lets User adjust screen by each OSD function.
4. DC/ DC Converter
This circuit supplies DC power for each device needing DC voltage of AVDD3.3V, DVDD3.3V, PVDD3.3V,
AVDD2.5V, DVDD2.5V, and 5VST.
L4973D5.1(U803) , the DC/DC controller IC converts input 12Vdc into +5Vdc and +3.3Vdc with peripheral circuit
composed of Coil (L805), condensing components (ZD801, C829, C830) and Regulators (U801, U821).
+3.3VMOD for LCD module power are switched by U802, switching FET, controlled by Microprocessor.