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LCD TELEVISION
LC-20Y19
America
CONTENTS
Safety instructions...................................................................................... 1
Adjustment instruction .............................................................................. 3
Trouble shooting ........................................................................................5
Method of software upgrading .......................................................................7
The unit working principle analysis............................................................... 10
Block diagram........................................................................................... 11
IC block diagram.........................................................................................12
Identification criteria for the bright spot and dark spot of the LCD screen............... 17
Wiring diagram ......................................................................................... 18
Troubleshooting charts................................................................................ 19
Schematic diagram .............................................................................. 22
APPENDIX: main assembly
Attention: This service manual is only for service personnel to take reference with. Before
servicing please read the following points carefully.
Safety instructions
1. Instructions
Be sure to switch off the power supply before replacing or welding any components or
inserting/plugging in connection wire Anti static measures to be taken (throughout the entire
production process!):
a) Do not touch here and there by hand at will;
b) Be sure to use anti static electric iron;
c) It's a must for the welder to wear anti static gloves.
Please refer to the detailed list before replacing components that have special safety requirements.
Do not change the specs and type at will.
2. Points for attention in servicing of LCD
2.1 Screens are different from one model to another and therefore not interchangeable. Be sure to
use the screen of the original model for replacement.
2.2 The operation voltage of LCD screen is 700-825V. Be sure to take proper measures in
protecting yourself and the machine when testing the system in the course of normal operation or
right after the power is switched off. Please do not touch the circuit or the metal part of the module
that is in operation mode. Relevant operation is possible only one minute after the power is
switched off.
2.3 Do not use any adapter that is not identical with the TV set. Otherwise it will cause fire or
damage to the set.
2.4 Never operate the set or do any installation work in bad environment such as wet bathroom,
laundry, kitchen, or nearby fire source, heating equipment and devices or exposure to sunlight etc.
Otherwise bad effect will result.
2.5 If any foreign substance such as water, liquid, metal slices or other matters happens to fall into
the module, be sure to cut the power off immediately and do not move anything on the module lest it
should cause fire or electric shock due to contact with the high voltage or short circuit.
2.6 Should there be smoke, abnormal smell or sound from the module, please shut the power off at
once. Likewise, if the screen is not working after the power is on or in the course of operation, the
power must be cut off immediately and no more operation is allowed under the same condition.
2.7 Do not pull out or plug in the connection wire when the module is in operation or just after the
power is off because in this case relatively high voltage still remains in the capacitor of the driving
circuit. Please wait at least one minute before the pulling out or plugging in the connection wire.
2.8 When operating or installing LCD please don't subject the LCD components to bending, twisting
or extrusion, collision lest mishap should result.
2.9 As most of the circuitry in LCD TV set is composed of CMOS integrated circuits, it's necessary
to pay attention to anti statics. Before servicing LCD TV make sure to take anti static measure and
ensure full grounding for all the parts that have to be grounded.
2.10 There are lots of connection wires between parts behind the LCD screen. When servicing or
moving the set please take care not to touch or scratch them. Once they are damaged the screen
1
would be unable to work and no way to get it repaired.
2.11 Special care must be taken in transporting or handling it. Exquisite shock vibration may lead to
breakage of screen glass or damage to driving circuit. Therefore it must be packed in a strong case
before the transportation or handling.
2.12 For the storage make sure to put it in a place where the environment can be controlled so as to
prevent the temperature and humidity from exceeding the limits as specified in the manual. For
prolonged storage, it is necessary to house it in an anti-moisture bag and put them altogether in one
place. The ambient conditions are tabulated as follows:
Temperature Scope for operation 0 ~ +50 oC
Scope for storage -20 ~ +60 oC
Humidity Scope for operation 20% ~ 85%
Scope for storage 10% ~ 90%
2.13 Display of a fixed picture for a long time may result in appearance of picture residue on the
screen, as commonly called "ghost shadow". The extent of the residual picture varies with the
maker of LCD screen. This phenomenon doesn't represent failure. This "ghost shadow" may remain
in the picture for a period of time (several minutes). But when operating it please avoid displaying
still picture in high brightness for a long time.
3. Points for attention during installation
3.1 The front panel of LCD screen is of glass. When installing it please make sure to put it in place.
3.2 For service or installation it's necessary to use specified screw lest it should damage the screen.
3.3 Be sure to take anti dust measures. Any foreign substance that happens to fall down between
the screen and the glass will affect the receiving and viewing effect
3.4 When dismantling or mounting the protective partition plate that is used for anti vibration and
insulation please take care to keep it in intactness so as to avoid hidden trouble.
3.5 Be sure to protect the cabinet from damage or scratch during service, dismantling or mounting.
2
Alignment instruction
1 Alignment equipment
PM5518 (video signal generator)
K-7253 (VGA signal generator)
CA210 (white balancer)
IF signal generator
Signal generator
Oscillograph
2 Alignment flow-chart
The alignment flow-chart is shown as fig-1
Write memory N300 and N400
To produce main board and power supply board
Check power supply board and main adjustment
All testing
Connect with central signal source, then check each function of TV(Station
missing, system identification, analog control etc.) , check the output of speaker
Input AV/S-video signal, and then check each function of AV/S-video
Input YPrPb signal and see if the display is normal under PC status
and check various functions (analog control), line/field center etc.
Check the accessories and pack them in box
Fig-1 adjustment flow-chart
3 Unit adjustments
3.1 Flash writing programs
Written memory N300 and N400.
3.2 Check power supply board
Turn off between power supply board and main board, after plug in power, testing X702 (pin1 and
pin5) power supply board voltage to be 12v and 5v.
3.3 main board adjustment
3.3.1 IF amplifier adjustment
a. Turn off the J201, J202, J203, J204, J205 and J5, input 38MHz(PAL SYSTEM) and 45.75MHz(N
3
SYSTEM) for X210, input 9v(