Q7T4-FP71G-99.L1C72.000-circuit_operation_theory.pdf

Q7T4-FP71G LCD Monitor Service Guide

Circuit Operation Theory

I. Introduction:

The Q7T4 is a 17” SXGA (1280x1024) , 16.2M colors(R, G, B 6-bit data+FRC data) TFT

LCD monitor. It’s an analog only interface LCD monitor with a 15 pins D-sub signal cable. it’s

compliant with VESA specification to offer a smart power management and power saving function. It

also offers OSD menu for users to control the adjustable items and get some information about this

monitor, and the best function is to offer users an easy method to set all adjustable items well just by

pressing one key, we called it “Auto key” which can auto adjusting all controlled items. Q7T4 also

offer DDC2 function to meet VESA standard.

II. Block diagram

The Q7T4 consists of a LCD module with 4 lamps, an power board, a control board ,and a

interface BD. The block diagram is shown as below.

LCD module with 4 lamps (backlight)

Inverter

Power

Interface board

Control board

D-Sub

AC power in

III. Circuit operation theory:

A-1.) Interface board diagram:

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Q7T4-FP71G LCD Monitor Service Guide

Circuit Operation Theory

MTV312M

64(AJ)

Clock

Generator

140MHz

ADC

RTD 2023

XGA

1280×1024

LCM

D-SUB

IIC

Keypad

(a) Circuit operation theory:

A basic operation theory for the interface board is to convert input signal into digital RGB .

Analog RGB signal is converted to digital signal through ADC. The microprocessor RTD2023

receives video data and optimizes the image automatically. It also supports 16 color from a 64k

palette bitmap OSD, and keypad controlling. The output data are sent to LCD module.

(b) IC introduction:

1.) DDC (Display Data Channel) function: We use DDC IC to support DDC/2B function. DDC

data is stored in 24C04(EEPROM). Those data related to LCD monitor specification. PC

can read them by “SDA” and “SCL” serial communication for I ² C communication for

DDC2B.

2.) RTD2023 IC: There are triple ADC, LVDS transmitter ,Scaling, and OSD functions in the

RTD2023 IC. Scaling IC is revolutionary scaling engine, capable of expanding any source

resolution to a highly uniform and sharp image, combined with the critically proven

integrated 8 bit triple-ADC and patented Rapid-lock digital clock recovery system. It also

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Q7T4-FP71G LCD Monitor Service Guide

Circuit Operation Theory

support detect mode and DPMS control.

3.) MTV312M64: To stored the source code which is accessed by MCU to run program.

4.) EEPROM: We use 24C04 to store all the adjustable data and user settings.And use 24C02 to

store DVI EDID data.

A-2.) Control board introduction:

There are 6 keys for user's control which includes “Power”, “Enter”, “Up/Plus”,

“Down/Minus” , “Exit”, and “iKey” . The following descriptions are the introduction of these keys.

(1) Power key: to turn/off power of monitor

(2) “Enter” key: to enter sub-menus or select items.

(3) “Up/Plus key: to select previous and to increase adjustment

(4) “Down/Minus” key: to select next and to decrease adjustment

(5) “Exit” key: to back to previous menu, or leave OSD (auto save)

(6) “iKey”: to perform auto adjustment

(7) LED: It indicates the DPMS status of this LCD monitor; green light means DPMS on (Normal

operating condition). Amber light means DPMS off (Powersaving).

A-3.) Power board diagram:

EMI Filter

Rectifier and

Isolation power

Rectifier and filter

Inverter circuit

filter

transformer

PWM controller

Switching element

Rectifier and filter

LDO regulator

Feedback Isolation

Fig.1

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Q7T4-FP71G LCD Monitor Service Guide

Circuit Operation Theory

#1 EMI Filter

This circuit (fig. 2) is designed to inhibit electrical and magnetic interference for meeting FCC, VDE,

VCCI standard requirements.

Fig. 2

#2 Rectifier and filter

AC Voltage (90-264V) is rectified and filtered by BD601, C605 (See Fig 3) and the DC Output

voltage is 1.4*(AC input). (See Fig.3)

Fig. 3

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Q7T4-FP71G LCD Monitor Service Guide

Circuit Operation Theory

#3 Switching element and Isolation power transformer

When the Q601 turns on, energy is stored in the transformer.

During Q601 turn-off period, the stored energy is delivered to the

secondary of transformer. R607, C607 and D601 is a snubber circuit.

R615 is current sense resistor to control output power. (See Fig.4)

Fig. 4

#4 Rectifier and filter

D701 and C703 are to produce DC output. L701 is used to suppress high Frequency switching spikes.

(See Fig.5)

Fig. 5

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