LD2006SI-2 is a LCD TV with
multiple functions. It adopts MST718 as main chip (MST718 has built-in MCU and
video processor). Video main board of this machine adopts 21903-X series PCB
(only small changes are made in PCB board numbers and service manual of
LD2006SI-2 adopts the video main board of 21903-5). This PCB integrates the
circuit of DVD function and DVB function on video main board. This PCB is
widely used and there are many derived machines. Now we will introduce
functions and machine structure of several derived machines one by one.
LT2000S
model
Based on LD2006SI-2, LT2000S cancels
DVD/card read function, but other circuit and components are totally the same
with those of LD2006SI-2. Compared with LD2006SI-2 on the aspect of composition
of the player, LT2000S has no PCB components of USB board /DVD button
board/video main board (DVD function circuit is absent).
LD1506SI-2 model
LD1506SI-2 is a 15” LCD TV, which changes
display screen to 15” LCD TFT screen on the basis of LD2006SI-2. According to
parameters requirements, drive means and inverter components are changed.
Differences on video main board: 1) LD1506SI-2 adopts LVDS output means, while
LD2006SI-2 adopts TTL output means, so the peripheral circuit of LCD drive
output part on MST718 has slight difference; 2) 15” screen adopts 5V power
supply, so IC702 is added to act as voltage stabilizing IC; 20” screen adopts
12V power supply, so there is no need to add voltage stabilizing IC; 3)
LD1506SI-2 adds VGA input circuit according to design requirements to make the
machine use as display; 4) LD1506SI-2 adopts adapter (AK083-3) to supply power,
while LD2006SI adopts internal power board to supply power, so power input end
is added on video main board.
LD1506SI-3 model
LD1506SI-3 changes display screen and MST718
ob the basis of LD1506SI-2. The main differences are: display screen is changed
to BOEHT150X02-100 15” TFT screen; main IC MST718BE is changed to MST718BU
PQFP; other parts are totally the same.
LT1500S-2 model
LT1500S-2 cancels DVD function on the basis of
LD1506SI-2 but other parts are totally the same.
LT1500S-3 model
LT1500S-3 changes display screen and MST718
on the basis of LT1500S-2. The main differences are: display screen is changed
to BOEHT150X02-100 15” TFT screen; main IC MST718BE is changed to MST718BU
PQFP; other parts are totally the same.
LD1906SI
LD1906SI changes display screen to 19” TFT
screen on the basis of LD1506SI-2. Because of this, boost components has
alteration, that is, boost components are changed to INV403 (working principle
is the same with INV607 and you may refer to “LT2002S Service Manual). Display
screen drive adopts LVDS input method and other circuits' working principle is
totally the same with that of LD2006SI-2.
LT1900S model
LT1900S cancels DVD function on the basis of
LD1906SI and other parts are totally the same with those of LD1906SI.
Parental control
settings
set-up of age restrictions to
prevent children from seeing undesirable discs.
Options: Any, Kid, G,PG, PG-13,
PGR, R,NC-17
Change password: set-up of a
four-digit password to change the level of age restrictions.
[Default option: 7890]
Initial setup
Press the RIGHT key to enter the
initial settings menu, then select the desired item using the cursor buttons
and press OK key for confirmation.
While being in this menu section, you cannot return
to the previous level by pressing the LEFT key.
LD2006SI is a 20” LCD_TV with
multiple functions, such as DVD playing and USB reading function.
Electronic scheme of TV part adopts 20” TFT
display screen+inverter components (INV604)+MST718+STV8216 +TDA7266P+ tuner JS
-6H2/T121. MST718 includes MCU/video A/D converter/LCD image processing
circuit. DVD part electronic scheme adopts MT1389HD+64M SDRAM+16M FLASH+D5954.
HD62 loader can smoothly read MPEG4/MP3/CD/DVD format discs and decode chip
MT1389HD may support USB and card read function.
Block diagram [common]
System control circuit is mainly
composed of reset circuit, clock circuit t, serial/parallel conversion circuit,
software program, EEPROM and MCU (MST718 is built inside). The built-in MCU of
MST718 is mainly responsible for the coordination and control of system of the
player. This MCU is connected with a 2M ROM externally, which is used to store
software and control function of the player. Since I/O port of MST718 is
limited, a serial/parallel conversion circuit (CD4094)is added to extend I/O
port. Functions may be adjusted through software. MST718 is connected with a
32k EEPROM externally, used to store user-set information.
System control circuit of the
player is composed of the built-in MCU of MST718 and software Program. Machine
power on: after 12V power is being rectified by U503, +5V power outputs to provide
for system control circuit. The reset circuit of system control circuit begins
to reset MST718, the red indicator light on remote control receiving board is
on under the control of STBY signal (high level), and this means machine enters
standby state.
The process from standby state to power on
state: after pressing POWER button on panel or wake code on remote controller,
pin 57 of MST718 changes from high level to low level, pin STBY outputs a low
level signal to make Q117 cutoff, /STBY skips to high level, STBY is divided to
3 parts: +5V power control circuit composed of Q3/U506; +12V power control
circuit composed of Q117/U511 and standby indication circuit on remote control
receiving board. Power supply of machine is normal, MST718 begins to output
reset and other control signal to reset
and control circuit of other module to make machine enter normal working state.
The process from working state to standby
state: when machine is in power-on state, after pressing POWER button on panel
or wake code on remote controller again, machine enters from power on to
standby, now pin 57 of MST718 outputs high level, /STBY pin output low level,
+5V power and +12V power of machine are cut off and machine enters standby
state.
NICAM: the core technoloy of “NICAM” is the NICAM728 technology
developed by BBC. Besides transmitting TV image and simulating mono-channel
signal, NICAM TV broadcasting system also transmits dual-channel digital coding
sound signal. NICAM is famous for clear treble and deep bass with the sound
quality close to listening to CD disk directly. In the aspect of SNR, dynamic
range and channel separation index, NICAM is far better than the current FM
accompany. As TV accompany, NICAM applies 3 kinds of working mode currently: 1)
Bilingual mode: NICAM transmits dual-channel digital sound relevant or
irrelevant to the current program and transmits 3-chan
nel sound signal together
with The original FM analog accompany, which are suitable for multi-language
areas; 2) Stereo mode: two digital channels of NICAM transmit left and right
channel sound signals of stereo separately, and the original FM analog
accompany only transmits mixed sound signals of 2 channels to be compatible
with TV set without NICAM function; 3) Mon0-channel mode: two channels of NICAM
transmit one channel sound signals and one channel data signal, which is equal
to providing 3-channel signals together with the original TV analog accompany.
Power-on mute: after power on, machine enters from standby to power on.
Because of R28, pin 11 of TDA726P is low level, now ONMUTE pin of Cd4094
outputs high level signal, OUTMUTE is high level, ,Q113/Q112/Q119 is saturated
on, machine enters mute state to realize power-on mute effect. After machine
starts up, ONMUTE switches to low level, Q113/Q112/Q119 cuts off to make pin 6
of TDA7266 high level, TDA7266 enters non-mute mode, the player has sound
output and power-on mute fulfills.
Power-off mute: when machines enters standby mode from working state,
ONMUTE pin outputs high level, OUTMUTE pin is high level signal, TDA7266 enters
mute state.
Power failure mute: when power of machine is switched off, Ce151 has been fully
charged when power on, after machine power switches off, Ce151 discharges
through Q118/D121 to make Q119 connected, now pin 6 of TDA7266 is low level to
realize power-off mute function.
When user use remote controller to mute the
machine, MUTE pin outputs high level signal to make Q119 saturated on, pin 6 of
TDA7266 is low level and TDA7266 enters mute mode.
Power circuit
Working principle: after AC power
is being rectified and filtered through power board, 12V power outputs. This
power is inputted to voltage stabilizing circuit of video main board through
socket Cn6 for voltage stabilizing. The power outputted after being voltage
stabilized is working power of each circuit.
Voltage stabilizing circuit on video main
board is divided to 3 parts: 1) +5VEXT outputted after being voltage stabilized
by Ic503 is mainly supplied for system control circuit; 2) +5V power outputted
after being voltage stabilized by is mainly supplied for DVD/DVB circuit; 3)
+12V voltage stabilizing and control circuit supply working voltage for rear
audio circuit.
Working principle:
+5VEXT voltage stabilizing circuit: after
the AC power inputted externally is being rectified/filtered through power
board, +12V power inputs to main video board. +12V power is divided to
multi-group power supply. One group inputs to the +5V voltage stabilizing
circuit composed by U503 (Ap1506) (Ap1506 is a voltage drop type voltage stabilizing
IC), after the 12V power inputted by power board is being voltage stabilized
through Ap1506, +5V power outputs directly. Pin 4 of Ap1506 is feedback end and
the resistance of its externally-connected resistor may adjust the output
voltage. To facilitate to differentiate +5VEXT mark ion circuit, this group of
power is mainly used for MST718 and each control circuit and supply working
power for the player when in standby working state.
Display screen working power control
circuit: display screen power has +5V/+12V. Display screen of this player
adopts +12V power supply, so L219 is not used in circuit but L16 is used for
power supply.
U502 in the picture is a MOS pipe used for
switch function to control power supply of display screen. This MOS pipe is controlled by PANELON
signal. When machine is in standby, PANELON outputs high level signal and U502
cuts off.
After machine power on, pin 74 of MST718
outputs low level signal to make Q505 cutoff, Q504/U502 is connected, +12V
power outputs to display screen through U502 and display screen begins to work.
Servicing Cases
Symptom: machine not
power on
after inserting power cord,
standby indicator light is on. After pressing power switch, green indicator
light flashes once and the machine power off.
Analysis and troubleshooting: according to
trouble symptom, the trouble mainly lies in power system. Firstly check whether
power board can work normally. Test whether power board flat cable +12V is
normal when power on; unplug the 6P power supply flat cable from power board to
main
board, after connecting with power, use
multimeter to check whether 12V voltage output in power board flat cable holder
is normal; insert the flat cable from main video board to power board and check
whether voltage output is normal; press POWER button, after voltage skips to
low level, machine power off, so that power board cannot load. To further
conform the causes, unplug power cord, connect a - 10 ohm resistor in power
board flat cable holder +12V position to ground (or change a power board for
test), after connecting with power, voltage in this position changes all the
time. According to the symptom, we can judge that power board cannot load. The
reason is that 12V filtering capacitor has electric leakage/switch transformer
has trouble, or the preliminary reverse clipping circuit cannot work normally,
or Ic1377 protects ahead of time. After test, we can find that the secondary
rectifying and filtering circuit is normal, so we judge that trouble is caused
by preliminary part. After power off, check one by one and find that Vd2 in
reverse clipping circuit has cut off. Change diode with the same specification,
trouble is removed.
Power not on.
After inserting power cord,
indicator light is not on. Press POWER button and machine cannot power on.
Analysis and troubleshooting: according to
trouble symptom, the trouble lies in power circuit and system circuit. Firstly
make sure whether power board has +12V voltage output; unplug 6P flat cable in
Cn6 position, check voltage and 12V output is normal, which means that power
board works normally. Press POWER button, check 12V voltage in Cn6 position and
it is normal, which means there is no load or short-circuit on main board.
Check 5V voltage of pin 2 of main board U503 and it is normal.
Test after words and find that two ends of
Ce503 have no 5V voltage output, so we doubt L503 has Trouble. Use multimeter
to test and find L503 has open circuit. When meets this symptom, do not hurry
to power on, use multimeter to test whether resistance on two ends of Ce503
becomes small. After test, 5V power resistance to ground is normal (note: as
for machine with abnormal resistance to ground, do not install L503 until
trouble is removed). After changing L503, power on and test. Machine works
normally and trouble is removed.
Machine not power on
After inserting power
cord, red indicator light flickers all the time. Press POWER button and machine
cannot power on.
Analysis and troubleshooting: according to
trouble symptom, the power part has short-circuit or large load. After power
off, firstly check +12V resistance to ground of main board and resistance does
not become small. Cut off the 6P power supply flat cable between power board
and
main board; connect a 10 ohm resistor
between 12V power cord and ground wire on power board to act as load; use
oscillograph to observe waveform on resistor, level changes all the time, and
power board protection circuit begins to work. Low voltage part has two-channel
over-voltage protection circuit, in which one performs constant output for 12V
power through Tl431 sampling; and the other makes the output less than 15.6V
through 15V voltage stabilizing pipe. Check the peripheral elements of the two
channels one by one and find that VD6/ 15V/0.5W has been stricken through.
Change voltage stabilizing pipe with the same specification, trouble is removed.
SMPS Schematic
TV has no sound output
Insert antenna, TV can receive
program, but speaker has no sound output. [External input audio is normal.]
NICAM signals are received from
tuner, which is used to receive TV signal and decompose the received signal to
audio/video signal to output. When meets this kind of trouble, do not hurry to
repair, firstly confirm whether there is sound output when in SCART, AV input
mode. After confirming, there is sound output in other mode now, which means
that U11 and speaker are good. Use oscillograph to test pin 14 of tuner MOINOIN
and waveform is normal. This signal is coupled through Ce134 to pin 73 of chip
U111 (STV8216), after processing inside chip, output from pin 28, 29 of
U9 to U112 for amplifying output. Test pin
18, 19 and they are normal. Test pin 28, 19 and there is no waveform output.
From this , we decide that the chip U111 may probably have trouble. Test power
supply voltage of pin 20 and it is normal and crystal oscillation waveform
output of chip is normal. Observe carefully and find that pin 28, 29 has the
possibility of rosin joint. Use iron to add tin and weld again. After power on
again, trouble is removed.
Tap
machine slightly and picture has disturbance. [After power on, image display is
normal and has white stripe flickering.]
If there is disturbance after
tapping machine, a certain or some elements in circuit may probably be not
contacted properly. According to trouble symptom, trouble lies in the connecting
board between display screen and main board. After checking machine flat cable,
there is no abnormality; then take down connecting board, check carefully and
find that there is a certain spring sheet in the socket on one end connecting
with screen has sunk. Change connecting board flat cable holder and trouble is
removed.
Black
screen when power-on.
From standby to power-on, screen
is black all the time and panel indicator light can display normally.
If screen is black when power-on,
firstly place the head of oscillograph near high voltage of boost board and
find that oscillograph has no inductive waveform, so we can make sure that
boost board has not outputted high voltage. use multi-meter to test +12V power
supply voltage of CN4 and it is normal. Use multimeter to test ON/OFF-INVERTER
end and it is high level when in standby and low level in power-on in normal
conditions, test Q102 B-E and it is connected, so we doubt that triode Q102 has
trouble; use multi-meter diode level to test Q102 and triode Q102 has been
stricken through. Change Q102 and trouble is removed.
Remote
control has no function.
When pressing buttons on remote
control, TV screen has no response.
Analysis and troubleshooting: test voltage
of 5V-IR pin of Cn105 and it is +4.96, which is normal.
When power is not on, test elements of
L148,R342 between pin 1 of CN105 and chip U101 and they are all normal. Test
pin 4 of remote control receiving board Cn801 to pin 1 of IR sensor and it is
normally connected. After power on, test voltage of pin 1 of CN105 and it is
+4.98V, which is also normal. Press Buttons on remote control and find that pin
1 voltage of CN105 has no change. Under normal conditions, when pressing remote
control, voltage changes from +4.98 to 3V plus several, which means remote
control information has been received, so trouble should be in remote control
receiver. After changing, trouble disappears.
In AV input mode, video
output end of SCART terminal has no vide signal output.
Select signal source in AV state,
switch on DVD Player to play demonstration disc and screen has no picture.
SCART is used to output signal to external TV and there is still no picture
display, but sound output is normal.
Trouble lies in video output
circuit. If video signals of LCD of this player are normal, it means external
input circuit is normal.
After being processed by MST718, externally
inputted video signals switch to digital video signals to output to display
screen; other signals output from pin 34 as analog signals to SCART terminal
through amplifying circuit to act as video output signals. Use oscillograph to
observe
Ce108, there is no signal output, but the
end that connects R42 and Q1 has signal output. Observe R2 carefully and the
surface has leakage. After power off, use iron to heat R2 and then cut off.
Change R2 with the same specification, trouble is removed.
Speaker has no sound
In any external input mode, there
is no sound output.
Analysis and troubleshooting: set signal
source in “AV" state, turn on DVD Player demonstration disc and use
oscillograph to test left/right speaker and find that there is no signal
waveform output, so we confirm trouble should appear in precious stage circuit.
test pin 8, 17 input pin of U112(TDA7226) and find that there is waveform
input, but pin 9, 20 have no waveform output. Then test power supply Loop and
+12V voltage changes to +10.8V after voltage drops, which is normal. Observe
whether pin Around has rosin joint or false welding. Weld again and trouble
exists, so it may be TDA7266 internal processing circuit that has trouble.
After changing U112, trouble disappears.
NICAM
has no function.
Press NICAMbutton on remote
control and bilingual mode, stereo mode and mono mode cannot be changed each
other.
After receiving “NICAM"
signal from tuner, NICAM outputs from pin 11, through the filtering circuit
composed by C301,C302, L301, enters pin 73 of STV8216, and then
restores to audio signal through internal
processing and then outputs to audio amplifying circuit from pin 28, 29, so
firstly use oscillograph to test whether waveform of pin 11 (SIF) is
normal. Then test pin 73 signal of U111
after filtering and find that waveform is normal and there is input but no
output, so we can make sure U9 has trouble; test each power supply voltage and
they are all normal. Confirm that
trouble lies in U111 and peripheral elements. Test IC power supply and voltage
is normal. Use oscillograph to test X301 and find that 27MHZ of X301 has no
oscillation. After changing X301, crystal oscillator has oscillation and
trouble is removed.
TV
cannot receive program.
When TV is receiving program,
there is no image output.
Analysis and troubleshooting: according to
trouble symptom, the trouble lies in tuner and peripheral elements. Channel
search is adjusted after the communication between IIC bus and main chip
MST718. Use oscillograph to observe pin 12 of tuner /CVBS and there is no
waveform output, and there should be 0.7V modulating waveform output on normal
cases. Check pin 3, 13 of tuner and +5V power supply and they are normal. Then check
IIC bus waveform and it is normal. Check pin 11 and there should be sine wave
with frequency 6MH and 1V output in normal cases but there is no actually, so
doubt tuner has trouble. Change tuner with the same specification, trouble is
removed.
Only one side of
headphone has sound output
in any signal source, left and
right channels of speaker output are normal. After inserting headphone, left
channel has no sound.
Sound signals are amplified
through TDA7266 after being outputted by STV8216 and then return to speaker
through headphone loop. When headphone is not inserted, left and right channels
of speaker are normal, so trouble lies in headphone loop obviously. Remove
headphone board, firstly check whether flat cable holder has joint welding or
rosin joint and it is normal after checking. Then check whether headphone
holder contacts well and it is normal. Check resistor R702, C705 on left
channel loop one by one and find R702 resistance is infinite. Use iron to heat
two ends of R702 and surface has leakage after heating, and R702 has been
damaged. Change elements with the same specification, trouble is removed.
Noise appears when
power on
Press POWER button on remote
control or control board to power on and off on each input mode and you may
hear “pop” noise during the courses.
Analysis and troubleshooting: according to
servicing experience, firstly check mute circuit when this kind of trouble
appears. Shown in the figure 3.3.1.3, when power on, MUTE signal changes from
low level to high level, and output high level through D120. When power off,
ce151 outputs high level through D121 and the diode D21, R71 inputted to mute
control circuit are added to base electrode of triode Q119 to make triode Q119
saturated on, now MUTE end is low level to realize power-on quieting effect.
Now there exists noise when power on and off, so we judge that trouble lies in
Q119 and its peripheral elements. After test, triode Q119 has been stricken
through. Change the triode with the relevant model and trouble is removed.
Do not read USB
Disc read is normal when in DVD
state; after inserting USB, USB data cannot be read out.
Analysis and troubleshooting: USB part is
processed after being switched by electronic switch ADG713 and then inputting
to Mt1389. Firstly check whether channel is normal, from USB board to main
board through 22P flat cable cord and then to video main board, and this flat
cable contact is bad. Firstly check whether USBM, USBP are normally connected
and whether there is short-circuit to ground. After checking, USB board works
normally. Then check lines on main board according to signal flow. USBP passes
through L158, so we judge that Mt1389 main chip cannot work normally. Check
power supply of each group and find that pin 49 USBVDD has no 3.3V voltage
input. Check peripheral circuit and find L191 has disconnected. Change L191
with the same specification and trouble is removed.
Disc
tray ejects out automatically.
Trouble description: in DVD state,
after loading disc, disc read is not available and disc tray ejects out
automatically.
When the above trouble appears,
firstly check whether loader flat cable has loosened. Check whether plug on
loader flat cable has been oxidized and it is normal, so doubt loader has
trouble. Change loader and trouble is removed.
Left and right channels
are not balanceable
Trouble description: sound of left speaker
is lower than that of right channel Analysis and troubleshooting: if channels
are not balanceable, software setup may probably have trouble. Firstly reset TV
part, trouble does not disappear, so we can judge that trouble lies in
hardware.
Disconnect power and check impedance of
left/right speaker and it is normal. Test when machine begins to play DVD test
disc normally. Connect pin 4, 12 of TDA7266, use oscillograph to observe the
amplitude of left/right channel output of TDA7266 and left channel amplitude is
smaller than that of right channel (note: now ground of oscillograph is
connected with OUT- and detect head is connected with OUT+), so trouble lies in
TDA7266. Change TDA7266 with the same specification and trouble is removed.
Do not read disc.
Trouble description: in DVD state,
CD/DVD disc cannot be read and then disc ejects out automatically.
Analysis and troubleshooting: check whether
loader components flat cable contacts well and there is no abnormality; remove
loader flat cable and check whether the contact position of plug and loader
clasp has been oxidated. Change loader but trouble still exists, so trouble
should lie in main board.
Power on, switch in DVD state, observe disc
reading condition of loader and main axis, focus, feed, trace action is normal,
but disc type cannot detected. Observe focus carefully and find object lens
twitters greatly, but cannot form slim light spot to shine on disc, so trouble
may probably lie in focus circuit. Check pin 24, 25 of focus feedback loop
Ba5954 and resistance value of R390 is normal. Use iron to heat C162, trouble
disappears, so capacitor loses effect. Change capacitor with the same
specification and trouble is removed.
No DVD image
Trouble description: other working
state of machine is normal, but DVD function cannot be used normally.
Analysis and troubleshooting: as for this
kind of trouble, firstly judge whether trouble lies in DVD function circuit.
Check Mt1389 power supply and it is normal, Mt1389 clock and reset signals are
normal, so we doubt FLASH program loses. Power on, switch in DVD state and use
oscillograph to observe whether FLASH pin has waveform. Remove FLASH, record
program again and trouble is removed.
Color
distortion in DVD state.
Trouble description: in DVD state,
when playing CD/DVD disc, sound output is normal but colour is to red with
shadow.
Analysis and troubleshooting: if colour has
distortion in DVD state, trouble may probably lie in SDRAM or Mt1389 or on CVBS
output line. Switch from DVD state to SCART state firstly; picture colour is
normal, so colour has distortion before MST718 input. CVBS outputs from Mt1389
and then enter MST718 through frequency selection network for image processing,
so trouble should lie in frequency selection network. Power off, use multimeter
to check whether each resistor and capacitor element has resistance sudden
change, and R395/75Ù has sudden change with only 15-ohm, which is caused by the
large attenuation of the signals outputted from DVD. Change resistor with the
same specification and trouble is removed.
Do not read DVD disc
Trouble description: in DVD state
CD playing is normal, DVD playing is not available and then DVD disc ejects out
automatically.
Analysis and troubleshooting: firstly check
whether DVD protection point of loader has joint welding phenomenon and there
is no abnormality. Change loader and trouble still exits.
The trouble lies in CD/DVD mode
switch circuit. CD/DVD mode switch is controlled by pin 112 I/O port level of
Mt1389 and VRCD and VRDVD switch is realized through selecting drive circuit.
When disc switches in CD and DVD, the switch of IOA in high and low level means
that Mt1389 control port outputs normally. When IOA is low level, TRDVD should
be low level and it is high level actually. Check R187 and circuit has
disconnected because of rosin joint. Use iron to weld again and confirm and
trouble is removed.
Troubleshooting Procedure
