LG M1921a Service Manual

							COLOR MONITOR
SERVICE MANUAL
Website:http://biz.LGservice.com
E-mail:http://www.LGEservice.com/techsup.html
CAUTION
BEFORE SERVICING THE UNIT, 
READ THE  SAFETY PRECAUTIONS IN THIS MANUAL.
CHASSIS NO. : CL-81
MODEL : M1721A (M1721A-BMF.A**NLF)
M1921A (M1921A-BMF.A**NLF)
*(      ) **Same model for Service 
						

							- 2 -
CONTENTS
SPECIFICATIONS
SPECIFICATIONS ................................................... 2
PRECAUTIONS ....................................................... 3
SERVICE PRECAUTIONS  ...................................... 4
TIMING CHART  ....................................................... 7
DISASSEMBLY ....................................................... 8
BLOCK DIAGRAM ................................................... 9
DESCRIPTION OF BLOCK DIAGRAM  ................. 10ADJUSTMENT ...................................................... 12
TROUBLESHOOTING GUIDE  .............................. 16
WIRING DIAGRAM  ............................................... 20
EXPLODED VIEW ...................................................21
REPLACEMENT PARTS LIST  ...............................23
SCHEMATIC DIAGRAM ......................................... 29
1. LCD CHARACTERISTICS
Type  : TFT Color LCD Module
Active Video Area : 17.0 inch-M1721A
: 19.0 inch-M1921A
Size : 358.5(V) x 296.5(H) x 17(D)-M1721A
: 
396.0(V) x 324.0(H) x 16.5(D)-M1921A
Pixel Pitch : 0.264mm x 0.264mm x RGB-M1721A
: 0.098mm x RGBmm x 0.294-M1921A
Color Depth : 6Bits with FRC, 16,777,216 colors 
Surface Treatment : Anti Glare, Hard Coating(3H)
Operating Mode : Normally white
Backlight Unit      : 4CCFL
Electrical Interface : LVDS
2. OPTICAL CHARACTERISTICS
2-1. Viewing Angle by Contrast Ratio  ≥10
M1721A
Left : -60° min., -70° typ Right : +60° min., +70° typ
Top : +60° min., +75° typ Bottom : -50° min., -65° typ
M1921A
Left : -70° min., -80° typ Right : +70° min., +80° typ
Top : +60° min., +70° typ Bottom : -50° min., -85° typ
2-2. Luminance : 160(min.), 250(typ.)
2-3  Contrast Ratio : 300(min.), 550(max.)-M1721A
: 350(min.), 650(max.)-M1921A
3. SIGNAL (Refer to the Timing Chart)
3-1. Analog Video Input
1) Video Input Range : 0~0.7V ± 5%
2) Video Termination Impedance : 75Ω±5%
3) Sync Type : Separate Sync.
4) Sync Level : TTL Low ≤0.8V, High ≥2.0V
3-2. Operating Frequency
Horizontal : 30 ~ 70kHz
Vertical : 56 ~ 75Hz
4. RESOLUTION
Analog Max : 1280 x 1024@60Hz5. POWER SUPPLY
5-1. Power 
AC 100-240Vac, 50/60Hz 
5-2. Power Consumption
6. ENVIRONMENT
5-1. Operating Temperature : 10°C ~ 35°C 
5-2. Operating Humidity : 20% ~ 80%
5-3. MTBF : 50,000 Hours (Min)
7. DIMENSIONS (with TILT/SWIVEL)
M1721A
Width : 394.4 mm (15.53)
Depth : 243 mm (9.57)
Height : 404 mm (15.91)
M1921A
Width : 445 mm (17.52)
Depth : 243 mm (9.57)
Height : 457 mm (17.99)
8. WEIGHT (with TILT/SWIVEL)
M1721A
Net. Weight : 4.5 kg (9.92 lbs)
Gross Weight : 6.2 kg (14.33 lbs)
M1921A
Net. Weight : 5.5 kg (12.13 lbs)
Gross Weight : 7.1 kg (15.66 lbs)
H/V SYNC
ON/ON
OFF/ON
ON/OFF
OFF/OFF
- MODEPOWER ON (NORMAL)
SLEEP MODE
POWER S/W OFF
VIDEO
ACTIVE
OFF
OFF
POWER CONSUMPTION
less than 40 W-M1721A
less than 45 W-M1921A
less than 1 W
less than 1 W
LED COLOR
BLUE
RED
OFF 
						

							PRECAUTION
- 3 -
WARNING FOR THE SAFETY-RELATED COMPONENT.
• There are some special components used in LCD
monitor that are important for safety. These parts are
marked   on the schematic diagram and the
replacement parts list.It is essential that these critical
parts should be replaced with the manufacturer’s
specified parts to prevent electric shock, fire or other
hazard.
• Do not modify original design without obtaining written
permission from manufacturer or you will void the
original parts and labor guarantee.
TAKE CARE DURING HANDLING THE LCD MODULE
WITH BACKLIGHT UNIT.
• Must mount the module using mounting holes arranged
in four corners.
• Do not press on the panel, edge of the frame strongly
or electric shock as this will result in damage to the
screen.
• Do not scratch or press on the panel with any sharp
objects, such as pencil or pen as this may result in
damage to the panel.
• Protect the module from the ESD as it may damage the
electronic circuit (C-MOS).
• Make certain that treatment person’s body are
grounded through wrist band.
• Do not leave the module in high temperature and in
areas of high humidity for a long time.
• The module not be exposed to the direct sunlight.
• Avoid contact with water as it may a short circuit within
the module.
• If the surface of panel become dirty, please wipe it off
with a softmaterial. (Cleaning with a dirty or rough cloth
may damage the panel.)WARNING
BE CAREFUL ELECTRIC SHOCK ! 
• If you want to replace with the new backlight (CCFL) or
inverter circuit, must disconnect the AC adapter
because high voltage appears at inverter circuit about
650Vrms.
• Handle with care wires or connectors of the inverter
circuit. If the wires are pressed cause short and may
burn or take fire.
Leakage Current Hot Check Circuit
CAUTION
Please use only a plastic screwdriver to protect yourself
from shock hazard during service operation.
1.5 Kohm/10W
To Instruments
exposed 
METALLIC PARTSGood Earth Ground
such as WATER PIPE,
CONDUIT etc.
AC Volt-meter 
						

							SERVICING PRECAUTIONS
- 4 -
CAUTION:Before servicing receivers covered by this
service manual and its supplements and addenda, read
and follow the SAFETY PRECAUTIONSon page 3 of this
publication.
NOTE:If unforeseen circumstances create conflict
between the following servicing precautions and any of the
safety precautions on page 3 of this publication, always
follow the safety precautions. Remember: Safety First.
General Servicing Precautions
1.  Always unplug the receiver AC power cord from the AC
power source before;
a. Removing or reinstalling any component, circuit
board module or any other receiver assembly.
b.  Disconnecting or reconnecting any receiver electrical
plug or other electrical connection.
c. Connecting a test substitute in parallel with an
electrolytic capacitor in the receiver.
CAUTION:A wrong part substitution or incorrect
polarity installation of electrolytic capacitors may
result in an explosion hazard.
d.  Discharging the picture tube anode.
2. Test high voltage only by measuring it with an
appropriate high voltage meter or other voltage
measuring device (DVM, FETVOM, etc) equipped with
a suitable high voltage probe.
Do not test high voltage by drawing an arc.
3. Discharge the picture tube anode only by (a) first
connecting one end of an insulated clip lead to the
degaussing or kine aquadag grounding system shield
at the point where the picture tube socket ground lead
is connected, and then (b) touch the other end of the
insulated clip lead to the picture tube anode button,
using an insulating handle to avoid personal contact
with high voltage.
4. Do not spray chemicals on or near this receiver or any
of its assemblies.
5. Unless specified otherwise in this service manual,
clean electrical contacts only by applying the following
mixture to the contacts with a pipe cleaner, cotton-
tipped stick or comparable non-abrasive applicator;
10% (by volume) Acetone and 90% (by volume)
isopropyl alcohol (90%-99% strength)
CAUTION:This is a flammable mixture.
Unless specified otherwise in this service manual,
lubrication of contacts in not required.
6. Do not defeat any plug/socket B+ voltage interlocks
with which receivers covered by this service manual
might be equipped.
7. Do not apply AC power to this instrument and/or any of
its electrical assemblies unless all solid-state device
heat sinks are correctly installed.
8. Always connect the test receiver ground lead to the
receiver chassis ground before connecting the test
receiver positive lead.
Always remove the test receiver ground lead last.9. Use with this receiver only the test fixtures specified in
this service manual.
CAUTION:Do not connect the test fixture ground strap
to any heat sink in this receiver.
Electrostatically Sensitive (ES) Devices
Some semiconductor (solid-state) devices can be
damaged easily by static electricity. Such components
commonly are called Electrostatically Sensitive (ES)
Devices.Examples of typical ES devices are integrated
circuits and some field-effect transistors and
semiconductor chip components. The following
techniques should be used to help reduce the incidence of
component damage caused by static by static electricity.
1. Immediately before handling any semiconductor
component or semiconductor-equipped assembly, drain
off any electrostatic charge on your body by touching a
known earth ground. Alternatively, obtain and wear a
commercially available discharging wrist strap device,
which should be removed to prevent potential shock
reasons prior to applying power to the unit under test.
2. After removing an electrical assembly equipped with
ES devices, place the assembly on a conductive
surface such as aluminum foil, to prevent electrostatic
charge buildup or exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or
unsolder ES devices.
4. Use only an anti-static type solder removal device.
Some solder removal devices not classified as anti-
static can generate electrical charges sufficient to
damage ES devices.
5. Do not use freon-propelled chemicals. These can
generate electrical charges sufficient to damage ES
devices.
6. Do not remove a replacement ES device from its
protective package until immediately before you are
ready to install it. (Most replacement ES devices are
packaged with leads electrically shorted together by
conductive foam, aluminum foil or comparable
conductive material).
7. Immediately before removing the protective material
from the leads of a replacement ES device, touch the
protective material to the chassis or circuit assembly
into which the device will be installed.
CAUTION: Be sure no power is applied to the chassis
or circuit, and observe all other safety precautions.
8. Minimize bodily motions when handling unpackaged
replacement ES devices. (Otherwise harmless motion
such as the brushing together of your clothes fabric or
the lifting  of your foot from a carpeted floor can
generate static electricity sufficient to damage an ES
device.) 
						

							- 5 -
General Soldering Guidelines
1. Use a grounded-tip, low-wattage soldering iron and
appropriate tip size and shape that will maintain tip
temperature within the range or 500。F to 600。F.
2. Use an appropriate gauge of RMA resin-core solder
composed of 60 parts tin/40 parts lead.
3.  Keep the soldering iron tip clean and well tinned.
4. Thoroughly clean the surfaces to be soldered. Use a
mall wire-bristle (0.5 inch, or 1.25cm) brush with a
metal handle.
Do not use freon-propelled spray-on cleaners.
5.  Use the following unsoldering technique
a. Allow the soldering iron tip to reach normal
temperature.
(500。F to 600。F)
b.  Heat the component lead until the solder melts.
c. Quickly draw the melted solder with an anti-static,
suction-type solder removal device or with solder
braid.
CAUTION: Work quickly to avoid overheating the
circuitboard printed foil.
6.  Use the following soldering technique.
a. Allow the soldering iron tip to reach a normal
temperature (500。F to 600。F)
b.  First, hold the soldering iron tip and solder the strand
against the component lead until the solder melts.
c. Quickly move the soldering iron tip to the junction of
the component lead and the printed circuit foil, and
hold it there only until the solder flows onto and
around both the component lead and the foil.
CAUTION:Work quickly to avoid overheating the
circuit board printed foil.
d. Closely inspect the solder area and remove any
excess or splashed solder with a small wire-bristle
brush.
IC Remove/Replacement
Some chassis circuit boards have slotted holes (oblong)
through which the IC leads are inserted and then bent flat
against the circuit foil. When holes are the slotted type,
the following technique should be used to remove and
replace the IC. When working with boards using the
familiar round hole, use the standard technique as
outlined in paragraphs 5 and 6 above.
Removal
1. Desolder and straighten each IC lead in one operation
by gently prying up on the lead with the soldering iron
tip as the solder melts.
2. Draw away the melted solder with an anti-static
suction-type solder removal device (or with solder
braid) before removing the IC.Replacement
1.  Carefully insert the replacement IC in the circuit board.
2. Carefully bend each IC lead against the circuit foil pad
and solder it.
3. Clean the soldered areas with a small wire-bristle
brush. (It is not necessary to reapply acrylic coating to
the areas).
Small-Signal Discrete Transistor
Removal/Replacement
1. Remove the defective transistor by clipping its leads as
close as possible to the component body.
2. Bend into a U shape the end of each of three leads
remaining on the circuit board.
3.  Bend into a U shape the replacement transistor leads.
4. Connect the replacement transistor leads to the
corresponding leads extending from the circuit board
and crimp the U with long nose pliers to insure metal
to metal contact then solder each connection.
Power Output, Transistor Device
Removal/Replacement
1. Heat and remove all solder from around the transistor
leads.
2. Remove the heat sink mounting screw (if so equipped).
3.  Carefully remove the transistor from the heat sink of the
circuit board.
4.  Insert new transistor in the circuit board.
5. Solder each transistor lead, and clip off excess lead.
6.  Replace heat sink.
Diode Removal/Replacement
1. Remove defective diode by clipping its leads as close
as possible to diode body.
2. Bend the two remaining leads perpendicular y to the
circuit board.
3. Observing diode polarity, wrap each lead of the new
diode around the corresponding lead on the circuit
board.
4.  Securely crimp each connection and solder it.
5. Inspect (on the circuit board copper side) the solder
joints of the two original leads. If they are not shiny,
reheat them and if necessary, apply additional solder.
Fuse and Conventional Resistor
Removal/Replacement
1.  Clip each fuse or resistor lead at top of the circuit board
hollow stake.
2. Securely crimp the leads of replacement component
around notch at stake top.
3.  Solder the connections.
CAUTION:Maintain original spacing between the
replaced component and adjacent components and the
circuit board to prevent excessive component
temperatures. 
						

							- 6 -
Circuit Board Foil Repair
Excessive heat applied to the copper foil of any printed
circuit board will weaken the adhesive that bonds the foil
to the circuit board causing the foil to separate from or
lift-off the board. The following guidelines and
procedures should be followed whenever this condition is
encountered.
At IC Connections
To repair a defective copper pattern at IC connections use
the following procedure to install a jumper wire on the
copper pattern side of the circuit board. (Use this
technique only on IC connections).
1. Carefully remove the damaged copper pattern with a
sharp knife. (Remove only as much copper as
absolutely necessary).
2. carefully scratch away the solder resist and acrylic
coating (if used) from the end of the remaining copper
pattern.
3. Bend a small U in one end of a small gauge jumper
wire and carefully crimp it around the IC pin. Solder the
IC connection.
4. Route the jumper wire along the path of the out-away
copper pattern and let it overlap the previously scraped
end of the good copper pattern. Solder the overlapped
area and clip off any excess jumper wire.At Other Connections
Use the following technique to repair the defective copper
pattern at connections other than IC Pins. This technique
involves the installation of a jumper wire on the
component side of the circuit board.
1. Remove the defective copper pattern with a sharp
knife.
Remove at least 1/4 inch of copper, to ensure that a
hazardous condition will not exist if the jumper wire
opens.
2. Trace along the copper pattern from both sides of the
pattern break and locate the nearest component that is
directly connected to the affected copper pattern.
3. Connect insulated 20-gauge jumper wire from the lead
of the nearest component on one side of the pattern
break to the lead of the nearest component on the
other side.
Carefully crimp and solder the connections.
CAUTION:Be sure the insulated jumper wire is
dressed so the it does not touch components or sharp
edges. 
						

							TIMING CHART
- 7 -
VIDEO
SYNC
B
C
EA
D
1 H(Pixels) + 25.175 31.469  800 640 16 96 48 640 x 350
V(Lines) - 70.09 449 350 37 2 60
2 H(Pixels) - 28.321 31.468 900 720 18 108 54 720 X 400
V(Lines) + 70.08 449 400 12 2 35
3 H(Pixels) - 25.175 31.469 800 640 16 96 48 640 x 480
V(Lines) - 59.94 525 480 10 2 33
4 H(Pixels) - 31.5 37.5 840 640 16 64 120 640 x 480
V(Lines) - 75 500 480 1 3 16
5 H(Pixels) + 40.0 37.879 1056 800 40 128 88 800 x 600
V(Lines) + 60.317 628 600 1 4 23
6 H(Pixels) + 49.5 46.875 1056 800 16 80 160 800 x 600
V(Lines) + 75.0 625 600 1 3 21
7 H(Pixels) +/- 57.283 49.725 1152 832 32 64 224 832 x 624
V(Lines) +/- 74.55 667 624 1 3 39
8 H(Pixels) - 65.0 48.363 1344 1024 24 136 160 1024 x 768
V(Lines) - 60.0 806 768 3 6 29
9 H(Pixels) - 78.75 60.123 1312 1024 16 96 176 1024 x 768
V(Lines) - 75.029 800 768 1 3 28
10 H(Pixels) + 108.0 63.981 1688 1280 48 112 248 1280 x 1024
V(Lines) + 60.02 1066 1024 1 3 38
MODEH / VSync 
PolarityDot
ClockFrequencyTotal
Period
( E )Video
Active 
Time ( A )Sync
Duration 
( D )Front
Porch 
( C )Blanking 
Time 
( B )Resolution 
						

							DISASSEMBLY
- 8 -
Hold the stand body & stand base.
1. Let the all latches are separated
2. Disassemble back cover. Separate body & stand base.
Remove the screws.
# 1
# 4 # 2
# 3
Disassemble Connector.
# 5 
						

							BLOCK DIAGRAM 
- 9 -
U101
J124J705
Option
5V
33V
5V
33VU30130P Wafer
U201 J103
R/G/B Out
from UOC
TN200
Tuner
Pack 
						

							DESCRIPTION OF BLOCK DIAGRAM
- 10 -
1. Power Supply Block (LIPS) 
This Block Generates DC Voltage (5V,15V) to Main Control system from AC Power (100-240V, 50/60Hz, 1.0A)
Also it has the inverter function converts input voltage to AC Rms value for the LCD lamp.
2. DC/DC Converter Block 
DC/DC Converter convert the input 5V, 15V to proper 3.3V, 5V, 8V, 12V for Main control system.
For shooting heat trouble, we use the DC/DC converting IC
3. Audio Amplifier 
This block is composed of TPA3005D2 and peripheral device.
The function of the audio amplifier is that to amplify audio L / R signal transmitted from audio decoder.
The audio signal is amplified according to pre-defined DC volume control curve.
4. Audio / Video / IF Decoder / Scaler 
This block is composed of LOC1 and peripheral devices.
1) Video Decoder
This Block Selects input Video signals (like CVBS, Y/C) and output RGB signal.
On decoding, We can control signal like Contrast,  Brightness, Sharpness, Color, Tint signals including
Adaptive Comb Filter.
2) Audio Decoder
This Block analyzes audio input signal through A/V Jack and PC audio and Tuner IF.
The analyzed signals transmitted to audio amplifier.
On decoding,  We can control signal like Bass, Treble.
3) IF Decoder
This block can change IF signal to audio and video signal that transmitted to Video/Audio decoder.
4) Scaler
This IC includes A/D Converter and LVDS Transmitter.
This IC is directly inputted Analog signal and transmits it to LCD Module.  
5) Micom
This block controls each IC through IIC communication line.
5. Switch IC (PI3V512QE) 
It is composed of PI3V512Q.
This IC selects between D-sub RGB signal and LOC1 RGB signal, and it transmits the selected signal to
video signal processor.
6. Tuner (included Tuner Pack (TN200)) 
Micom controls this through IIC Line.
Tuner makes IF and transmits IF signal to LOC1.