LG TCH-M900 Service Manual
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❍
SECTION 1. SUMMARY
• SERVICING PRECAUTIONS
..........................................................................................................
1-2
• ESD PRECAUTIONS
.......................................................................................................................
1-3
• SPECIFICATIONS
...........................................................................................................................
1-4
❍
SECTION 2. ELECTRICAL
• ELECTRICAL TROUBLESHOOTING GUIDE
.................................................................................
2-1
• CD PART TROUBLESHOOTING GUIDE
.........................................................................................
2-3
• WAVEFORMS OF MAJOR CHECK POINT
..................................................................................
2-11
• INTERNAL BLOCK DIAGRAM of ICs
............................................................................................
2-13
• BLOCK DIAGRAM
.........................................................................................................................
2-25
• SCHEMATIC DIAGRAM
................................................................................................................
2-27
- MAIN SCHEMATIC DIAGRAM
...................................................................................................
2-27
- FRONT SCHEMATIC DIAGRAM
................................................................................................
2-29
- CDP SCHEMATIC DIAGRAM
....................................................................................................
2-31
• PRINTED CIRCUIT DIAGRAM
......................................................................................................
2-33
❍
SECTION 3. CABINET MAIN CHASSIS & MECHANISM
• EXPLODED VIEW
...........................................................................................................................
3-1
❍
SECTION 4. REPLACEMENT PARTS LIST
....................................................................
4-1
[CONTENTS]
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❏ SERVICING PRECAUTIONS
➊ Always disconnect the power source before:
1) Removing or reinstalling any component, circuit board, module or any other instrument assembly.
2) Disconnecting or reconnecting any instrument electrical plug or other electrical connection.
3) Connecting a test substitute in parallel with an electrolytic capacitor in the instrument.
CAUTION: A wrong part substitution or incorrect polarity installation of electrolytic capacitors may result in
an explosion hazard.
➋ Do not defeat any plug/socket B+ voltage interlocks with which instruments covered by this service
manual might be equipped.
❸ Do not apply power to this instrument and or any of its electrical assemblies unless all solid-state
device heat sinks are correctly installed.
❹ Always connect a test instrument’s ground lead to the instrument chassis ground before
connecting the test instrument positive lead. Always remove the test instrument ground lead last.
1) The service precautions are indicated or printed on the cabinet, chassis or components. When servicing,
follow the printed or indicated service precautions and service materials.
2) The Components used in the unit have a specified conflammability and dielectric strength. When
replacing any components, use components which have the same ratings. Components marked in
the circuit diagram are important for safety or for the characteristics of the unit. Always replace with the
exact components.
3) An insulation tube or tape is sometimes used and some components are raised above the printed writing
board for safety. The internal wiring is sometimes clamped to prevent contact with heating components.
Install them as they were.
4) After servicing always check that the removed screws, components and wiring have been installed
correctly and that the portion around the service part has not been damaged. Further check the insulation
between the blades of attachment plug and accessible conductive parts.
SECTION 1. SUMMARY
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❏
ESD PRECAUTIONS
[Electrostatically Sensitive Devices (ESD)]
Some semiconductor (solid state) devices can be damaged easily by static electricity. Such omponents
commonly are called Electrostatically Sensitive Devices (ESD). Examples of typical ESD 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 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 for potential
shock reasons prior to applying power to the unit under test.
2) After removing an electrical assembly equipped with ESD 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 ESD devices.
4) Use only an anti-static solder removal device. Some solder removal devices not classified as “anti-static”
can generate electrical charges sufficient to damage ESD devices.
5) Do not use freon-propelled chemicals. These can generate electrical charges sufficient to damage ESD
devices.
6) Do not remove a replacement ESD device from its protective package until immediately before you are
ready to install it. (Most replacement ESD 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 ESD 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 ESD 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 ESD device).
[CAUTION. GRAPHIC SYMBOLS]
THE LIGHTNING FLASH WITH APROWHEAD SYMBOL. WITHIN AN EQUILATERAL
TRIANGLE, IS INTENDED TO ALERT THE SERVICE PERSONNEL TO THE PRESENCE
OF UNINSULATED “DANGEROUS VOLTAGE” THAT MAY BE OF SUFFICIENT
MAGNITUDE TO CONSTITUTE A RISK OF ELECTRIC SHOCK.
THE EXCLAMATION POINT WITHIN AN EQUILATERAL TRIANGLE IS INTENDED TO
ALERT THE SERVICE PERSONNEL TO THE PRESENCE OF IMPORTANT SAFETY
INFORMATION IN SERVICE LITERATURE.
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1. GENERAL
Power requirements
.....................................................................................................................
DC12V~15V
Ground system
...................................................................................................................................
Negative
Dimensions(W x H x D)
......................................................................................................
188 x 58 x 166mm
Weight
..............................................................................................................................................
Net: 1.3kg
2. RADIO SECTION
FM AM(MW)
Frequency range 65.0~74.0MHz(Optional), 522~1,620kHz
87.5~108MHz (Optional:530~1,710kHz/ 520~1,620kHz)
Intermediate frequency 10.8MHz 450kHz
Usable sensitivity 12dBµV 32dBµV
Signal to noise ratio 55dB 45dB
3. COMPACT DISC SECTION
Frequency response
.....................................................................................................................
40Hz~20kHz
Channel separation
......................................................................................................................
50dB(1kHz)
Signal to noise ratio ..................................................................................................................................
60dB
4. AUDIO SECTION
Maximum output power
.......................................................................................................................
50W x 4
Speaker impedance
...............................................................................................................
4Ω x 4 or 8Ω x 4
NOTE: The design and specifications are subject to change without notice in the sourse of product
improvement.
❏
SPECIFICATIONS
- 2-1 -
SECTION 2. ELECTRICAL
❏ ELECTRICAL TROUBLESHOOTING GUIDE
Any Key power on.
Is power turnd on?
DISC loading?
Does initial reading occur?
Can disc be played?
Is audio output supplied?
Check power supply circuitry.
Q260, Q380, Q381, IC401 Pin76
IC201 Pin2
Check loading supply circuitry.
Q350,Q351,PN505, IC401 Pin27
Check laser circuitry.
Q501, IC502
Check focusing circuitry.
Q501,IC502
Check DISC.
Check tracking servo circuitry.
Q501,IC502
Check audio circuitry.
IC502,IC601,IC801
OK
YES
YES
YES
YES
YES
YES
NO
NO
NO
NO
NO
(1) No Power.
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YES
YES
YES
YES
YES
YES
(2) LCD light abnornal.
Any Key power on.
(without DISC)
Do display LCD then light?
Check voltage in the power
supply circuitry.
Power supply circuitry
defective.
Q380,Q381,IC403
Reset circuit defective.
IC201 Surrounding circuit
defective.
X401, C413,C414 defective.
Q260, PN401 front PCB
pattern defective.
IC401, Pin38, 40, 47, 48 front
PCB pattern defective.
IC901, Surrounding circuit
PCB pattern defective.
Is u-com IC401 reset circuit
normal? Pin10
Is u-com IC401 keyin Pin16, 44
71 5volt input?
Is u-com IC401 Pin 38,40,47,48
output waveform normal?
Is IC901 Com1, Com2, Com3
output waveform normal?
Display LCD connector defective.
Is u-com IC401X1, X2 terminal
Pin14, 15 input?
OSC : 9.8304MHz
NO
NO
NO
NO
NO
NO
NO
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