Diamond View DV172 User manual

Diamond View LCD Monitor
DV172 / DV172B (B=Black Cosmetic)
Service Guide
February 2003
Distributed by
Mitsubishi Electric Australia Pty. Ltd.
A.B.N. 58 001 215 792
348 Victoria Road
RYDALMERE NSW 2116
Australia
Telephone [phone]

ii
Copyright
Copyright ã1996 by the Company. All rights reserved. No part of this publication may be
reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language or
computer language, in any form or by any means, electronic, mechanical, magnetic, optical,
chemical, manual or otherwise, without the prior written permission of the Company.
Disclaimer
The Company makes no representations or warranties, either expressed or implied, with respect to
the contents hereof and specifically disclaims any warranties, merchantability or fitness for any
particular purpose. Further, the Company reserves the right to reserve this publication and to make
changes from time to time in the contents hereof without obligation of the Company to notify any
person of such revision or changes.

iii
Diamond View LCD Monitor
DV172 / DV172B
(B = Black Cosmetic’s)
Manual Contents
Section
1. Engineering Specifications
2. Circuit Operation Theory
3. Alignment procedure
4. Trouble Shooting
5. Parts Lists (DV172 & DV172B)
6. Schematic Diagrams
7. Assembly

DV172 LCD Monitor Service Guide Engineering Specification
1
Table of Contents
1. INTRODUCTION ...................................................................................................................................2
2. ELECTRICAL CHARACTERISTICS.................................................................................................3
2.1 POWER SUPPLY......................................................................................................................................3
2.2 SIGNAL INTERFACE ...............................................................................................................................3
2.3 VIDEO PERFORMANCE...........................................................................................................................5
2.4 SCAN RANGE.........................................................................................................................................5
2.5 PLUG & PLAY DDC2B SUPPORT ..........................................................................................................5
2.6 SUPPORT TIMINGS.................................................................................................................................5
3. OPERATIONAL & FUNCTIONAL SPECIFICATION.....................................................................6
3.1 VIDEO PERFORMANCE...........................................................................................................................6
3.2 BRIGHTNESS ADJUSTABLE RANGE........................................................................................................6
3.3 ACOUSTICAL NOISE ..............................................................................................................................6
3.4 AUDIO PERFORMANCE ..........................................................................................................................7
4. LCD CHARACTERISTICS...................................................................................................................7
4.1 THE PHYSICAL DEFINITION & TECHNOLOGY SUMMARY OF LCD PANEL ...............................................7
5. USER CONTROLS.................................................................................................................................8
5.1 USER’S HARDWARE CONTROL DEFINITION: ...........................................................................................8
5.2 OSD CONTROL FUNCTION DEFINITION..................................................................................................8
6. MECHANICAL CHARACTERISTICS...............................................................................................9
6.1 DIMENSION ...........................................................................................................................................9
6.2 WEIGHT ................................................................................................................................................9
6.3 PLASTIC ................................................................................................................................................9
6.4 CARTON ................................................................................................................................................9
7. CERTIFICATION...................................................................................................................................9
APPENDIX: PHYSICAL DIMENSION FRONT VIEW AND SIDE VIEW......................................11

DV172 LCD Monitor Service Guide Engineering Specification
2
1. Introduction
This specification describes DV172, a 17.0” dual interface color TFT LCD monitor with speakers
supported. The display supports up to 1280x1024/75Hz resolution & refresh rate and 262144 colors with
dithering. The features summary is as below,
Feature items Specifications Remark
Panel supplier & Panel type of supplier AUO M170EN05 TN with Film type
Actual Size Diagonal display 17.0" Panel display size
Actual Resolution display SXGA(1280x1024) Panel display resolution
Viewing Angle (at Contrast Ratio ≧10)
+/- 70 degrees Horizontal (typ.)
+/- 70 degrees Vertical (typ.)
+/- 60 degrees Horizontal (min.)
+/- 60 degrees Vertical (min.) Panel spec
Analog interface with Scaling supported Yes With 15 pin D-sub connector
DVI interface with Scaling supported Yes With 24 pin DVI connector.
Video interface with Scaling supported No N.A.
Max resolution mode supported 1280 x 1024 at 75Hz
Number of Display Colors supported 262144 (with dithering) Panel driver is 6 bit
Contrast Ratio 250:1 (min.), 500:1 (typ.)
Luminance
200 cd/m2 (min.),
260 cd/m2 (typ.)
At R,G,B saturated condition
(Default “User” color setting)
AC power input Yes 90-264 Volts, 47-63 Hz.
DC power input(with AC power adapter) No N.A.
DPMS supported Yes < 3 watts
LED indicator for power status showed Yes Green/Amber/Non
OSD for control & information supported Yes
Multi-language supported for OSD Yes 6 languages
Buttons control supported Yes 6 buttons including 1 monitor power on/off control button.
Flywheel control supported No N.A.
Scaling function supported Yes Genesis gm5120
Auto adjustment function supported Yes “Auto” key function
DDC function supported(EDID ver. 1.3) Yes DDC2B only
Audio speakers supported Yes
Audio Jack(input connector) supported Yes
Earphone Jack(input connector) supported No N.A.
Microphone function supported No N.A.
Mechanical Tilt base design Yes From 0 to +20 degree
VESA wall mounting design Yes
Mechanical Rotate design No N.A.
Mechanical Lift base design No N.A.

DV172 LCD Monitor Service Guide Engineering Specification
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2. Electrical Characteristics
2.1 Power supply
Item Condition Spec OK N.A Remark
Input Voltage range Universal input full range 90~264VAC /47~63Hz √
Input Current range 90 ~ 264VAC < 2.0 Arms √
Power Consumption Normal “On” operation < 50 Watts √LED: Green
DPMS DPMS “Off” state < 3 Watts √LED: Amber
Inrush Current 110 VAC
220 VAC
< 30 A (peak)
< 60 A (peak)
√Cold-start
Earth Leakage Current 264 VAC/50Hz < 3.5 mA √
Hi-Pot 1. 1500VAC, 1 sec
2. Ground test: 30A, 1sec
Without damage
< 0.1 ohm
√(on-line test)
(in-lab test)
Power Line Transient IEC1000-4-4 1KV √
IEC1000-4-5 (Surge) Common: 2KV,
Differential: 1KV
√
CCFL operation range 90 ~ 264VAC 6mA ~ 15mA √Each connector
CCFL Frequency 90 ~ 264VAC 40KHz ~ 80KHz √
Power cord Color: White or Black
Length: 1800 +/- 20 mm
√Depends on shipping
requirement (99 level)
2.2 Signal interface
Item Condition Spec OK N.A Remark
Signal Cable 15 pin D-Sub Color: White or Black
Length: 1600 +/- 20 mm
√Depends on shipping
requirement (99 level)
15 pin D-sub connector See Note-1 √For 15 pin D-sub
Pin assignment
24 pin DVI connector See Note-2 √For 24 pin DVI
Video input Signal type-1 Separate analog R,G,B signals √For 15 pin D-sub
Level(R,G,B signals) 700 mV (peak to peak) √
Impedance(R,G,B signals) 75 Ohms +/- 1.5 Ohms √
Signal type-2 TMDS signals √For 24 pin DVI
Single-ended input swing
voltage (V-swing)
200mV≤V-swing≤780mV √
Impedance(TMDS signals) 100 Ohms +/- 10 Ohms √
Sync input Signal type Separate H/V-sync
Composite H/V-sync
(Positive/Negative)
√For 15 pin D-sub
Level Logic High: 2.4V ~ 5.5V
Logic Low: 0V ~ 0.5V
(TTL level)
√Refer to VESA VSIS
Standard V1R1
Impedance Minimum 2.2KΩ(pull down) √10KΩfor application
Sync Pulse Width (SPW) 0.7μs < H-SPW
1H < V-SPW
√
Note-1: The pin assignment of 15 pin D-sub connector:
51
10 6
15 11

DV172 LCD Monitor Service Guide Engineering Specification
4
Pin Signal Assignment Pin Signal Assignment
1 Red video 9 PC5V (+5 volt power)
2 Green video 10 Sync Ground
3 Blue video 11 Ground
4 Ground 12 SDA
5 Ground 13 H-Sync (or H+V)
6 Red Ground 14 V-sync
7 Green Ground 15 SCL
8 Blue Ground
Note-2: The pin assignment of 24 pins DVI connector: (C1 ~ C5 are NC)
12345678
910 11 12 13 14 15 16
17 18 19 20 21 22 23 24
C1 C2
C3 C4
C5
Pin Signal Assignment Pin Signal Assignment
1 TMDS RX2- 16 Hot Plug Detect
2 TMDS RX2+ 17 TMDS RX0-
3 TMDS Ground 18 TMDS RX0+
4 Floating 19 TMDS Ground
5 Floating 20 Floating
6 DDC Clock 21 Floating
7 DDC Data 22 TMDS Ground
8 Floating 23 TMDS Clock+
9 TMDS RX1- 24 TMDS Clock-
10 TMDS RX1+ C1 Floating (NC)
11 TMDS Ground C2 Floating (NC)
12 Floating C3 Floating (NC)
13 Floating C4 Floating (NC)
14 +5V Power C5 Floating (NC)
15 Ground

DV172 LCD Monitor Service Guide Engineering Specification
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2.3 Video performance
Item Condition Spec OK N.A Remark
Max. support Pixel rate 135 MHz
√
Max. Resolution 1280 x 1024 √
Rise time + Fall time < 3.7 ns
(50% of minimum pixel
clock period)
√1280x1024 @ 75Hz
(max. support timing)
Settling Time after
overshoot /undershoot
< 5% final full-scale value √Refer to VESA VSIS
Standard V1R1
Overshoot/Undershoot < 12% of step function
voltage level over the full
voltage range
√Refer to VESA VSIS
Standard V1R1
2.4 Scan range
Item Condition Spec OK N.A Remark
Horizontal 31 ~ 81KHz
√
Vertical 56 ~ 75 Hz √Without Frame buffer
2.5 Plug & Play DDC2B Support
Item Condition Spec OK N.A Remark
DDC channel type DDC2B √
EDID Version 1.3
√Refer to FP767-MEA
DV172 C212 S/W spec
document to see the
detailed EDID data
definition..
2.6 Support Timings
Input Timing Actual Output
Resolution Horizontal
Frequency (KHz) Vertical Frequency (Hz) Dot Clock Frequency (MHz) Actual display Resolution OK N.A Remark
640x350 31.47(P) 70.08(N) 25.17 1280x943
√DOS
720x400 31.47(N) 70.08(P) 28.32 1280x1024
√DOS
640x480 31.47(N) 60.00(N) 25.18 1280x1024
√DOS
640x480 35.00(N) 67.00(N) 30.24 1280x1024
√Macintosh
640x480 37.86(N) 72.80(N) 31.5 1280x1024
√VESA
640x480 37.50(N) 75.00(N) 31.5 1280x1024
√VESA
800x600 37.88(P) 60.32(P) 40.00 1280x1024
√VESA
800x600 48.08(P) 72.19(P) 50.00 1280x1024
√VESA
800x600 46.86(P) 75.00(P) 49.50 1280x1024
√VESA
832X624 49.72(N) 74.55(N) 57.29 1280x1024
√Macintosh
1024x768 48.36(N) 60.00(N) 65.00 1280x1024
√VESA
1024x768 56.48(N) 70.10(N) 75.00 1280x1024
√VESA
1024x768 60.02(P) 75.00(P) 78.75 1280x1024
√VESA

DV172 LCD Monitor Service Guide Engineering Specification
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Input Timing Actual Output
Resolution Horizontal
Frequency (KHz) Vertical Frequency (Hz) Dot Clock Frequency (MHz) Actual display Resolution OK N.A Remark
1024X768 60.24(N) 74.93(N) 80.00 1280x1024
√Macintosh
1152x864 67.50(P) 75.00(P) 108.00 1280x1024
√VESA
1152x870 68.68(N) 75.06(N) 100.00 1280x1024
√Macintosh
1152x900 61.80(N) 66.00(N) 94.50 1280x1024
√SUN 66
1152x900 71.81(N) 76.14(N) 108.00 1280x1024
√SUN
1280x1024 64.00(P) 60.00(P) 108.00 1280x1024
√VESA
1280x1024 75.83(N) 71.53(N) 128.00 1280x1024
√IBM1
1280x1024 80.00(P) 75.00(P) 135.00 1280x1024
√VESA
1280x1024 81.18(N) 76.16(N) 135.09 1280x1024
√SPARC2
Note-2: “P”, “N” stands for “Positive”, “Negative” polarity of incoming H-sync/V-sync (input timing)
3. Operational & Functional Specification
3.1 Video performance
Item Condition Spec OK N.A Remark
Resolution Any input resolution modes
which are under 1280x1024
1280 x1024 √
Contrast ratio 250:1(min.), 500:1 (typ.) √
Brightness At R,G,B saturated condition
(Default “User” color setting)
200 cd/m2(min.)
260 cd/m2(typ.)
√
Response time Rising + Falling time 16 ms(typ.), 25ms(max.) √
Viewing angle At Contrast ratio ≧10 R/L: 60 degrees (min.)
70 degrees (typ.)
√
At Contrast ratio ≧10 U/D: 60 degrees (min.)
70 degrees (typ.)
√
CIE coordinate of White (0.31, 0.33) +/- (0.03, 0.03) √
Display colors 262144 color with dithering √18 bits with
dithering
3.2 Brightness Adjustable Range
Item Condition Spec OK N.A Remark
Brightness adjustable range
At Max. Contrast level &
Full-white color pattern
(Max. brightness value –
Min. brightness value)
≧40 cd/㎡
√
3.3 Acoustical Noise
Item Condition Spec OK N.A Remark
Acoustical Noise At 1 meter distance
& “Audio” function disabled ≦40 dB/A √

DV172 LCD Monitor Service Guide Engineering Specification
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3.4 Audio performance
Item Condition Spec OK N.A Remark
Preamp + Power amp
(1)Output power 1 Wrms/CH @ 1KHz √Real output
(2)THD (@ 1W) <10%
√
(3)S/N ratio 40dB
√
Speaker Driver
(1)Nominal impedance 8 ohm
√
(2)Maximum input power 2W/CH
√
(3)Frequency response 12KHz
√
(4)Mean sound pressure level 83 ± 3 dB √
(5)Size 28x 40 mm
√
Audio Control
(1)Volume range 0 ~100 levels √
(2)Mute On/Off
√
4. LCD Characteristics
4.1 The Physical definition & Technology summary of LCD panel
Item Condition Spec OK N.ARemark
LCD Supplier AUO √
Panel type of Supplier M170EN05 √
Screen Diagonal 432mm(17.0”) √
Display area Unit=mm 337.920(H) x 270.336(V) √
Physical Size Unit=mm 358.5(W) x 296.5(H) x 19.0(V) √
Weight Unit=gram 1900 (typ.) √
Technology TN with Film √
Pixel pitch Unit=mm 0.264 x 0.264 √Per one triad
Pixel arrangement R,G,B vertical stripe √
Display mode Normally white √
Support color 262K colors(R,G, B 6-bit data) √

DV172 LCD Monitor Service Guide Engineering Specification
8
5. User Controls
5.1 User’s hardware control definition:
Item Condition Spec OK N.ARemark
Monitor Power button √
Enter button √
▲/Inc. button
√
▼/Dec. button
√
Exit button √
Auto button √
Mute button √
Input source select button √
5.2 OSD control function definition
Item Condition Spec OK N.ARemark
Contrast
√See Table 3
Brightness
√
Horizontal Position √
Vertical Position √
Pixel Clock √
Phase
√
Color Temperature C1: 9300
C2: 6500
C3: 5800
User: Separate R,G,B adjustment
√
OSD Position OSD Horizontal position
OSD Vertical position
√
Language
6 languages √
OSD Time From 5 sec to 60 sec √
Vo l u m e
√
Hot key for Contrast √
Hot key for Brightness √
Hot key for Volume √
Auto adjustment Auto-Geometry/Color √
Information
For input timing √
Mute
√
Input Source select √
Recall
√
* The detailed Firmware functions’ specification, please refer to C212, S/W spec document.

DV172 LCD Monitor Service Guide Engineering Specification
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6. Mechanical Characteristics
6.1 Dimension
Item Condition Spec OK N.ARemark
Bezel opening 340x272.4 mm
√Refer to Table 6
Monitor without Stand L x W x H mm 382.7x118x402.85 mm √
Monitor with Stand L x W x H mm 382.7x200x404.3 mm √
Carton Box (outside) L x W x H mm 495x450x158 mm √
Tilt and Swivel range Tilt : 0/20 degree
Swivel:0 degrees
√
6.2 Weight
Item Condition Spec OK N.ARemark
Monitor (Net) 4.7Kg
√
Monitor with packing (Gross) 6.5Kg
√
6.3 Plastic
Item Condition Spec OK N.ARemark
Flammability 94HB
√
Heat deflection To ABS 65 ℃√
UV stability ABS Delta E < 8.0 √MPR2/TCO
Resin MPR2 : ABS
(VW55/VE0856/D350)
√
Texture MT-11030
√
Color Pearl White
√
6.4 Carton
Item Condition Spec OK N.ARemark
Color
Kraft √
Material
B Flute √
Compression strength 530 KGF √
Burst Strength 16 KGF/cm2 √
Stacked quantity 13 Layers √
7. Certification
Item Condition Spec OK N.ARemark
Environment Green design API Doc. 715-C49 √ISO14000
Requirement
Blue Angel German Standard √
E-2000 Switzerland
√
EPA USA Standard
√
EN61000-3-2 Harmonics
√

DV172 LCD Monitor Service Guide Engineering Specification
10
TCO92/95
√
TCO99
√
PC-Monitor Microsoft Windows PC98/99
√
DPMS VESA
√
DDC 2B Version 1.3 √
USB External
√
Safety UL (USA) UL 1950 3rd edition √
CSA (Canada) C22.2 No. 950-M95 √
FIMKO EN60950
√
IEC950
√
EN60950
√
73/23/EEC
√
CB
√
TUV/GS EN60950
√
CCIB (China)
√
EIAJ/JEIDA (Japan)
√
Item Condition Spec OK N.ARemark
NOM (Mexico)
√
JEON (Korea)
√
EZU
√
PSB
√
EMC CE Mark 89/336/EEC
√
FCC (USA) Class B √
EN55022 Class B
√
CISPR 22 Class B √
VCCI (Japan) Class B √
BSMI (Taiwan)
√
C-Tick (Australia) AS3548
√
RRL (Korean)
√
X- Ray Requirement DHHS (21 CFR) USA X- Ray Standard √
DNHW
√
PTB German X- Ray standard √
MPRII
√
MPRIII
√
Ergonomics ZH1/618 German ergonomic
√
ISO 9241-3 -7 & 8 √

DV172 LCD Monitor Service Guide Engineering Specification
11
Appendix: Physical Dimension Front View and Side view
3 8 2 . 7
3 4 0 . 0
2 5 0
3 5 7 . 5
7 8 . 5
2 0 0
2 7 2 . 4

DV172 LCD Monitor Service Guide Circuit Operation Theory
1
I. Introduction:
DV172 model is a 17” SXGA (1280x1024) 18 bits color TFT LCD monitor with multi-media function.
The features of DV172 are as below,
(a)Dual signal input supported for a 15pins D-sub and a DVI-D input connectors.
(b)It’s compliant with VESA DPMS spec to offer a smart power management and power saving function.
(c)OSD menu supported for users to control the adjustable items and get some information about this monitor.
(d)”Auto” button function supported to offer users an easy method to set all adjustable & controlled items well
by just pressing one button, “Auto”.
(e)VESA DDC2B function supported.
(f)Audio function supported with 2 speakers.
II. Block diagram
DV172 consists of a head and a stand (base). The head consists of a LCD module with 4 lamps, a power
board (include AC-DC, inverter power & audio circuit), a control board and an interface board. The block
diagram is shown as below.
Inverter
+
AC-DC board
+
Audio circuit
TFT-LCD module with 4 CCFL(backlight)
Control board
AC input
EEPROM
Flash
ROM
Scaler
(Genesis
gm5120)
Interface board
To
backlight
D-sub
connector
Analog RGB signals
AC
socket
Power sequence
circuit
Scaler Power
ADC
DDC
IC
Audio
IN
Speaker Speaker
LVDS xtmr
DVI-D
connector
TMDS rcvr
DDC
IC
DVI-D(TMDS) signals
III. Circuit operation theory for electrical circuits in HEAD of DV172:
A.) Interface board diagram:

DV172 LCD Monitor Service Guide Circuit Operation Theory
2
Interface Board
A/D
TMDS
MCU
Scaling
OSD
To
LCD
module
EEPROM FLASH- ROM
Gm5120
DDCDDC
RX0
RX1
RX2
RXC
Red
Green
Blue
Vsync
Hsync
(H+V)
SCL
SDA
DSCL
DSDA
(a) Circuit operation theory: (The scaling IC used in DV172 is Genesis gm5120)
A basic operation theory for this interface board in Analog input signals processing, the scaling IC
inside A/D converter will convert analog input signals of Red, Green and Blue to 8 bits digital signals of
Red, Green and Blue, and for interface board in DVI-D(TMDS) digital input signals processing, the scaling
IC inside TMDS receiver will convert TMDS signals to 8 bits digital signals of Red, Green and Blue. Then
no matter input signals Analog or DVI-D(TMDS) format are, they have been converted to 8 bits digital Red,
Green and Blue signals, and the scaling IC inside MCU and scaling control circuit will start to do timing
signal detecting and calculating to output the proper LCD panel signals to LCD panel circuit.
The timing signal detecting function in the scaling IC is to detect whether input H-sync, V-sync or
digital pixel clock signals’ status have been changed by host PC system, then it will do short-time picture
blanking, signal processing and converting again if input signals have been changed.
The scaling IC inside OSD circuit will be programmed to an OSD menu which can be showed on the
screen to offer adjustable functions to end-users to control and adjust some picture settings by themselves.
After the scaling IC internal signal processing is done, it will output the digital RGB data, the H-sync,
V-sync, pixel clock and DE(data enable) signal to LVDS transmitter and then to LCD panel driver circuit.
There are two kinds of EEPROM used in interface board, one is 24C02 which is used to store DDC

DV172 LCD Monitor Service Guide Circuit Operation Theory
3
data, we also call it, DDC IC, and another is to store OSD common data and those picture controlled and
data.
Flash-Rom is to store the source code which will be accessed by the scaling IC inside MCU to run
program.
(b) IC introduction:
1.) DDC (Display Data Channel) function: We use DDC IC to support DDC/2B function. DDC data is
stored in 24C02(EEPROM). Those data related to LCD monitor specification. PC can read them by
“SDA” and “SCL”(“DSDA” & “DSCL” for DVI-D input port) serial communication for I2C
communication for DDC2B.
2.) Gm5120 IC: There are A/DC, TMDS receiver, Scaling, OSD, MCU in the gm5120 IC. Scaling IC is
revolutionary scaling engine, capable of expanding any source resolution to a highly uniform and sharp
image or down scaling from UXGA, combined with the critically proven integrated 8 bit triple-ADC
and patented Rapid-lock digital clock recovery system. It also support detect mode and DPMS control.
MCU control unit, it controls all the functions of this interface board, just like the OSD display setting,
the adjustable items, adjusted data storage, the external IIC communication, support DDC2B.
3.) EEPROM: All the adjustable data and user settings are stored in EEPROM (24C16).
4.) FLASH ROM: To store source code which will be accessed by Scaling IC inside MCU to run program.
B.) Power board diagram:
EMI Filter Rectifier and
filter
Isolation power
transformer
Rectifier and filter Audio Amp and
Pre-Amp
PWM controller Switching element
Feedback Isolation
Inverter circuit
Rectifier and filter
LDO regulator

DV172 LCD Monitor Service Guide Circuit Operation Theory
4
(a) EMI Filter
This circuit (fig. 2) is designed to inhibit electrical and magnetic interference for meeting FCC, VDE,
VCCI standard requirements.
Fig. 2
(b) 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
(c) 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)

DV172 LCD Monitor Service Guide Circuit Operation Theory
5
Fig. 4
(d) Rectifier and filter
D701 and C703 are to produce DC output. L701 and C704 are to suppress high Frequency switching
spikes. (See Fig.5)
Fig. 5
(e) PWM Controller
The current mode control IC UC3842B is used to control PWM. When the VCC terminal of it gets
16V, IC601 turns on. +5V will be set up at Pin8 through soft start circuit, which includes R617, C611,
D606 and D605. R616 and C610 generate a fixed frequency saw-tooth wave at Pin4.

DV172 LCD Monitor Service Guide Circuit Operation Theory
6
Fig. 6
(f) Feedback circuit
PC123 is a photo-coupler and TL431 is a shunt regulation. They are used to detect the output voltage
change and be the primary and secondary isolation. When output voltage changes, the feedback voltage
will be compared and duty cycle will be decided to control the correct output voltage. (See Fig.7)
Fig. 7