Model LCD-407 circuit description

1 shows the power switch circuit with the band:

Logic IC 301 BU4069 group containing six inverters (Inverter), used as two independent selector
switch, that the power switch (Power
on-off) and the band selector (Band vhf-uhf).
First turn the power supply IC Pin14, C340 instant storage capacitor potential is zero, so that IC
Pin2 / 3 for high potential, IC Pin4 low potential,
Q302 non-current drive, high-impedance state between the CE, and Q301 has not turned on, the
other main power supply circuit can not at this time is through capacitor C341
R320 charged to high potentials.
While pressing the Power button (not release back) when, C341 stored high potential capacitor
C340 through R319 charge, so that high potential. Which IC
Pin2 / 3 to a low potential, IC Pin4 compared with high potential, and promote through R318 Q302,
it was a low resistance state between the CE, while the Q301 turns on, it
He circuit to be powered while the Power button to return to after release, due to IC Pin2 / 3 is low,
the C341 is stored high potential, by R320 discharged.
If pressing the Power button again, the C341 is much larger than the value of capacitor C340, C340
and therefore stored in the high potential discharge by C341 and R320
Completed at this time IC Pin1 low potential, IC Pin2 / 3 to a high potential, IC Pin4 compared with
low potential, Q301 and Q302 is closed again. More consecutive
Touch and pressure, to form the circuit back and forth to change the on-off action.
Another group of the same band switching circuit, set to boot from the C342 power supply, IC
Pin9/10 low potential, Pin8 high potential at this time
Q303 turns on, Q304 off, VHF Tuner to get some power.
When the button is depressed Band, IC Pin9/10 high potential, Pin8 low potential. Turn off at this
time Q303, Q304 turns on, UHF Tuner Department
Were to be powered.
2 lamp high pressure generator (D to A) circuit description:
Power first by R401, R410, R411 to provide Q406, Q407 required DC bias. And by the L401, T401
to Q406, Q407
Collector, to produce intermittent oscillation by the T401 secondary ring Pin1 / 2, to provide
positive feedback signal to the Q406, Q407 base, so that oscillation can be sustained while
T401 secondary ring Pin8/10, provides ultra-high pressure lamp current push by C407. C406 may
amend the oscillation frequency, C404, L401 to prevent vibration
Swing frequency, through the power to interfere with other circuits.
Q403, Q401 and its peripheral circuits, providing lamp delay start function, to prevent transient
screen. Powered C402 instantaneous short circuit, the Q403
Turn, turn again to Q401, R401 off the DC bias, the Q406, Q407 is not immediately start-up,
subject to the C402 is charged, the Q403,
Q401 off, while the Q406, Q407 DC bias voltage is restored, in order to start-up, lit the lamp
display. R402, D401 in off moments, so
C402 discharges quickly, so as not to re-boot an exception.
3 shows the brightness control circuit:
Q204,

Q204, Q205 and its peripheral circuits, through the brightness control keys Up / Down, adjust the
Q205 output DC-bit, and then the R272, R242 to
IC202 Pin6, change the screen brightness (the higher the potential darker picture)
When the Down button, when pressed, C261 through R266 high impedance charge slowly, so that
potential increases when the Up button when pressed, C261 through R268 high
Resistance slowly discharge, the potential was decreased. Q204 FET (field effect transistor) source
pole output circuit, with a high input impedance, low impedance output characteristics, it can be
extremely C261 DC-bit gate, through the very source output. Q205 FET may be regarded as ultra-
high impedance resistor (as in the reverse bias voltage of the diode), to provide
Q204 bias current required due to Q204, Q205's high impedance, the C261 can not be discharged by
the surrounding components, and thus remain potential long-lasting
Change.
4 voice circuit description:
Sound

Sound IF signal output from the IF processor IC Pin18, after C125, CC125, CF103 filter out other
images and sync signals, and then enter
IC Pin10 sound IF amplifier through the IC, the signal amplification to saturation, by the Pin16
output, and then the R126, CF104, C136 type IC
Pin15, FM demodulation circuit response by the internal audio signal, the audio output from the IC
Pin13, C139, and external audio input through the terminal, to IC501 audio
Volume control circuit by Pin14 input by Pin6 UP and Pin7 DOWN the button control, adjust the
volume increase or decrease, then the Pin15 output, and then by
C505, R504, R518 set the volume level, the input amplifier IC502 Pin3 amplification by Pin5
output to external speakers side by C506
Son, and to promote speakers produce sound.
The main function of the relevant line components are as follows:
C125, CC125, L109 high-pass filter can filter out low frequency sync signal and video signal.
CF103 sound IF passband filter with color images and high-frequency signals.
R126, CF104 FM detector to generate the required RF carrier signal.
R127, C136 former CF104 output impedance matching, the latter for the DC-blocking capacitors.
R128, C138 FM de-emphasis circuit, to provide high audio rejection ratio of about 75US to
improve the noise figure.
C139, C520 Volume controller input and output of the DC-blocking capacitors.
R501 IC502 negative feedback resistor is used to control the IC amplification.
C503, R503 with high audio phase shift, in order to prevent high frequency parasitic oscillation
generated.
R517 headset to reduce the output power, to prevent overload break the sound headphones.
C507 located on the headphone end to prevent high frequency parasitic oscillation generated.
C508 IC104 output DC blocking capacitors, and decided to output the audio of the low frequency
response.
C127, C126 sound IF amplifier bias voltage and signal bypassed.
R130, C137 to change the sound IF amplifier Pin14 DC bits, control the audio output size.
R116, C128, C129 sound intermediate frequency amplifier circuit with the power to pay back.
R502, C502 to pay back the audio power amplifier with the power circuit.
R507, C510 RC constant setting of the digital pulse oscillation frequency, the volume can be
adjusted to change the digital speed of change.
C511 at the beginning of supply, the internal volume control, set at a fixed level on the (46DB).
R512, C509 after shutdown to provide IC501 required to support current trace.
5 tuner and intermediate frequency processor circuit description:

TV RF signal received by the antenna, after C103, C102 to the tuner input Pin8, in its internal
amplification and difference frequency conversion, transmission by Pin1
The IF signal. This 4.5-6.5MHz bandwidth of the signal, then amplified by Q101 and F101 comb
filter, select the IF signal path, the input frequency at
Processor IC101 Pin 6 / 7. And then by its internal amplification, and the resonant frequency of the
coil located Pin19/20, select the IF signal detector to be processed by the Pin18
Video output signal after demodulation and sound IF signal.
Tuner Pin2 is the main power, Pin3 / 6, respectively VHF and UHF band of the power control, and
Pin4 was the High and Low VHF
Two bands of the power options control. Pin5 external control voltage, the internal tuner can change
the resonant frequency of the carrier, so that the external input of the TV signal difference frequency
conversion
Fixed frequency of the IF signal. Pin7 to the AGC control voltage, the internal TV tuner can change
the zoom level of the signal gain. (Generally with the voltage level of about
Changes in 0-30db)
The TV antenna RF signal strength, distance changes with the intensity of regional radio stations.
(By the weak signal can be a strong signal to 36db 86db, about 50db
Of change) and to avoid too strong signal or amplified overload, resulting in image distortion, the
need to use AGC circuit generates 50db of gain control is generally put IF
Preceding the first control amplifier 20db, and tuner control after anterior 30db. That the antenna
signal enhancement from 36 to 56db range, IC101 within the image
Peak detector circuit starts with the image of high and low volatility, reduce the IF gain self-control
to avoid image overload distortion, while the tuner input of the IC101 Pin3
AGC voltage is constant, in order to maintain maximum RF gain of the antenna signal is enhanced
by a 56 to 86db range, the IF gain is not further reduced with the signal strength.
At this point IC101 Pin3 output of the voltage, but with the signal strength can be gradually
increased, and output to the tuner Pin7, to reduce its internal RF amplifier stage of the gain.
IC101 Pin21 of the resonant coil T101, the frequency will be offset by the IF signal to produce DC
voltage relative to the AFT, the Pin 17 output.
This voltage is adjusted in the mid point, exactly half the supply voltage, if the IF frequency is high
then the voltage drop, and vice versa for the increase in the formation of intermediate S-curve. Scan
Tuning
IC102 is the use of this feature to search and lock the radio frequency is adjusted points.
C102, C113, C115, C116 for the DC-blocking capacitors.
C105, C106, C107, C108, C109, C110 RF bypass capacitor, the internal RF tuner to prevent
radiation leakage.
R173 tuner IF output of the load impedance matching.
R104, R105, R107 to Q101 IF amplifier stage bias resistor.
R103, C112 to Q101 IF amplifier stage to pay back even the power circuit.
L104, R106 and CF101 former resonance to enhance the gain of the input capacitance, which
reduces the value of L104Q to prevent ringing.
L105, C122 cross-linked back to IC101 power circuit.
R113, R114 set the tuner AGC voltage of 1.5V optimal operating point. (AGC does not start)
C120, C124 AGC filter capacitor to remove the peak voltage of the signal components associated
with the image.
C119, R109, R108, C117 IF amplifier stage peak AGC circuit control components.
SVR101, R112 set IC101 Pin4 voltage to determine the start of the RF AGC IF signal strength.
R111 IC101 Pin24 voltage can be set to change the image signal of Pin18 output amplitude.
6 units selected scan circuit description:
IC101Pin18 the image signal output through C131, R121, R120, C132 filter out high frequency
components, by Pin22 input, and then the internal buffer
Red amplified by Pin23 output synchronization signal for IC102 Pin7 input and feedback to the
class and after the horizontal sync pulse Pin6 comparison phase. If phase lock
Set, then Pin4 to a high potential output (usually Pin4 to low)
IC102 supply, Pin26 will repeat the output sawtooth variation with time of the DC voltage from
0.5V up to 4.5V, and then gradually declined back to
0.5V, the rate of change determined by the Pin12 of R164 This voltage is about 7 times by IC103
put that range to 30V, the input tuner
Pin5, to change its internal resonant frequency, the radio signal search when the radio signal is close
to the IF output video signal, the composition of the horizontal sync pulse, the
Pin7 sent back to the input and display Pin6 the sync signal lock, the scanning speed is
automatically reduced in order to use Pin8 voltage input of the AFT, and the offset
Shift of the voltage characteristics of the S-curve, look for points to be locked frequency is adjusted
so that the voltage remains constant selection station, fixed station to receive the image
Pin9 voltage by the Up and Down buttons of the control (usually in half the supply voltage)
pressing Up key to Pin26 boost the output voltage, pressure
Down button to Pin26 output voltage drops, the level of direction can be controlled radio stations.
Pin27 determined by the external voltage level, choose to work in the VHF or UHF
Band in the VHF band, because it contains two bands Low and High, to be able to manually switch
between its voltage switching point determined by the Pin10, that the VHF
Low band began to scan, when the scanning voltage is higher than Pin10 Pin26, the band
automatically switch to VHF High, and Pin26 voltage and by the most scanning
Low began to rise, until the voltage reaches the highest point of the scan after the reversal, down to
reach the aforementioned switching point, the band automatically switch back to VHF Low, and
scanning electron
Pressure has continued to decline from the highest point, again and again.
Pin2 / 3 will be scanned with high and low voltage, the output level corresponding to the phase of
the pulse can be used to show on the screen, respectively, the scale of VHF and UHF radio
Position, but this pulse on the radio locked automatically disappear after scanning stops, so as not to
interfere with the normal screen, but the radio is locked, can also use the Channel button to change
Change Pin17 potential, so that Pin2 / 3 to output channel position display. Pin28 is with the VHF
High / Low of the band switching, the output high and low voltage control
Tuner, select the VHF band's work. Pin23/24/25 of the DC-bit, voltage can be set to scan the highest
point, to determine the scope of the band ratings can also be used
Adjust the scale calibration of high-end radio while Pin19/20/21 of the DC-bit, adjustable scanning
voltage curve, the radio can be used to adjust the low end of the scale school
Standard. Pin18 in the scanning process to maintain a high potential side to Q103 conduction, and
thus reduce the potential to IC101 Pin14, turn off the audio circuit to eliminate
Noise-free radio station in addition also on-Q102, reducing lock sensitivity, to avoid side-band radio
wave with the impact of slow scanning speed.
L108, C149, C150 to pay back for the IC102 power supply circuit connected
C154 decided to Pin2 / 3 of the output pulse width, which is the thickness of the cylindrical screen
channel display.
C142, C143 to Pin4 charging capacitor, control lock completion time, ie disappearance of the
cylindrical channel show time.
R141, C144 level pulse shaping capacitors to correct external input of the phase waveform Pin6.
D103, D104 antihypertensive effect, so choose low-end voltage drop (this voltage is amplified by
IC103 higher).
7 image processing circuit description:
Image signal from the IC101 Pin18 output, through R118, L107, CF102 sound IF signal is filtered
and then amplified by Q201 buffer, then
To the external AV input terminal for external input image of choice. The selection of the video
signal, the black and white composition (Y signal), by
R204, R208, C203 into the IC201 Pin24, in its internal buffer amplifier, and is subject to Pin25 and
Pin23 to set the dc bias, respectively, control image
The sharpness (that is, the image frequency gain) and contrast (ie, image gain), by the Pin22 output
followed by the Pin21 input, at which point the DC reference potential,
Also subject to Pin20 of the control to adjust the brightness of the image of the bottom (ie black
level of the DC-bit), while the image signal of the synchronization signal component, then the
buffer by Q203
Amplified, and then by R206, C207, R207, C208 circuit filter out low frequency of the sync signal
into the IC201 Pin15, except for the internal signal processing IC, the
Amplified by the Pin16 output to the LCD display to control the image scanning phase.
Image signal of the color signal components (including color images and color synchronization),
then the buffer amplified by Q203 through R205, C204, C205, and Lee
With C209, L201 resonance frequency of the color signals pass into the IC201 Pin2. In its internal
amplification, and is subject to Pin28 set the DC bias, control color film
As the intensity (ie, gain color images), by Pin4 output by the Pin10/11 enter individual's RY, BY
signal processing circuit, the IC internal use
The color subcarrier demodulation for signal processing. Demodulation of RY and BY signals in the
IC and Pin21 input of the Y signal, combined into R, G, B
Signal, respectively, by Pin17, 18,19 output to IC202 RGB signal processor.
Pin27 color subcarrier generated by the resonant frequency of two signals, by Pin8 external DC bias
for the micro-adjustment, in addition to 2 times the frequency of treatment.
Then Pin5 DC-bit, subcarrier phase control (ie, hue control), and by the phase lock loop circuit Pin8
locked frequency, so that it can completely and radio signals to keep
The same frequency and phase. The principle of using the color sync signal input Pin2, Pin15 of the
IC by the horizontal sync pulse removed, and Pin27 production
Poor health of the resonant carrier frequency, the filter is converted to DC offset voltage, you can
automatically correct the resonant carrier offset, locking the color sub-carrier radio signal. Pin6 self-
Moving color gain control circuit to prevent excessive color signal modulation caused by the
phenomenon of saturation gamut. Pin9 as achromatic circuit, the radio does not transmit color
signals can be
Automatically shut down within the color demodulation circuit, the output directly to black and
white images, in order to eliminate noise on the image of the color markings. Pin26 the level of the
external potential can be determined IC
The color demodulation mode to NTSC or PAL. Pin12 input from the LCD screen is back, the level
has been locked pulse synchronization for PAL systems
The phase control with every scan. (For PAL system BY modulation signal is required for each
interval of a horizontal line, automatically reverse the positive and negative phase, but in the NTSC
system
Can not)
C201, C203 DC-blocking capacitors for the low-frequency video signal to pass.
R204, L204, C249 color for the filter circuit to filter out signal components.
R206, R209 with the IC input requirements, setting black and white image level.
R255, C222 to use its time constant, the level of synchronization with the external input signal to
remove the color sync signal.
Q202 input image signal in the external work, by Q201's emitter-bias conduction, so IC102 to stop
scanning.
R170 to provide external input video signal of the standard load, and can reduce the Q201 emitter
bias against Q202 turns on the scanner failure.
8. RGB signal processor circuit description:
Pin19/20/21 input from the RGB signal, amplified by the internal processing, and is subject to Pin 7
from the LCD screen, the inverting input of the FRP pulse Q206
Wave control, with each level of cycle interval converted RGB signal polarity, and then the IC's
internal switching circuits, and RGB signals plus image overlap after the merger,
By the Pin13 / 12/11 output, sent to the LCD display circuit to generate the image, adjust Pin 2 / 3
external DC-bit, which can control the brightness low R and B by
Benefits, adjusted Pin 4 / 5 external DC-bit, you can control the R and B, respectively, high
brightness gain, both with the adjustment, the level of brightness in the image, able to reach
RGB white balance to the demand. Pin15/16/17 the high level of external RGB signal input can be
used to display text on the image or mark, now
By the IC102 input, display VHF and UHF radio channel location of the green and blue column
markers. Pin 6 DC-bit, and from Q204/Q205
Related to the brightness control to adjust the image brightness.
L202, C240, C241 circuit for the IC202 cross-linked retirement
R277, R278, R272 to set the brightness of the DC-bit variable range.
9 DC power conversion circuit description (D to D):
IC302 power supply, the internal regulator circuit from the Pin8 output and power supply Pin7
resonant circuit, and then fixed by the Pin4 output pulse oscillation cycle,
For the promotion of Q305 and T301, the T301 secondary groups, respectively, have different
voltage rectifier and filtered by the individual, is converted to DC power supply
Other circuits require. Pin6 output of the T301, the main power base, can set the voltage divider
circuit level, feedback to the IC302 Pin1, amplified by its internal
By the Pin2 output, and internal control Pin4 the output pulse duty cycle (ie ON-OFF time ratio),
T301 to adjust the output voltage level when the
SVR302 partial pressure increased after, IC302 Pin1 and Pin2 reduces elevated, Pin4 the output of
the pulse duty cycle value is lower (ie, high potential for a short while low
Potential duration lengthened), and then the T301 converted to the secondary. Due to pulse phase
contrast, the T301 Pin5 high potential output pulse time longer, and the D305 turns
Between the increase in output increase as the DC bit. Pin6 for the short-circuit protection circuit,
when the T301 Pin5 abnormal main power output short circuit occurs, IC302 Pin1 no
Feedback zero potential, Pin2 is increased to 1.5V, and the IC charge Pin6, to potential increases,
the cut Pin4 output to protect the IC302.
R305, R306, C307 RC time constant that determines the pulse oscillation cycle.
R307, R308, C309 Pin6 DC-bit set to 0.9V, and the use of C309 required charging time, so start
slow start when short-circuit protection circuit,
To prevent malfunction.
T301 Pin6 the main base for the 5V power supply, L302, C321, C322 cross-linked circuits to its
back.
T301 Pin3 to 33V power supply for the tuner IC and tuner circuits.
T301 Pin4 to 18V power supply for liquid crystal display circuit is used.
T301 Pin5 to 10V power supply for volume controller IC and RGB processor IC circuit after the
class to use.
T301 Pin7 negative for the 7V supply, negative power supply circuit for LCD use.