Structurally, the GoldStar CKT4442B, chassis PC-05X2 TV is made in a plastic case in which a picture tube and the main board are installed, on which vertical and horizontal scanning circuits are mounted, a power supply, a video signal processing channel, a synchronization circuit, a full radio channel, including an audio circuit.
A control module with a remote control circuit, an interface board with a VCR, a secam/pal transcoder and a kinescope board with output video amplifiers are connected to this board using connectors. Remote control circuit It is made on a single microcircuit M708B1 which performs functions similar to the domestically produced KR1506HL1 microcircuit used in TVs of the USCT type. M708B1 contains a clock generator, the external elements of which are capacitors C01 and C02, and a resonator X01. When you press one of the buttons, one of pins 9-14 is connected to one of 4-8.
Each such connection generates a specific command in the IC, which is allocated in the form of a sequence of pulses at pin 19. From this pin, the pulses go to the power amplifier on TR01 and TR02, in the collector circuit, which includes the transmitting infrared LEDs 1R01 and 1R02. Signal sent by the remote control. is received by the photodiode of the photodetector board. On the transistor Q01 of this board, a photocurrent amplifier is made, an amplifier-former of a pulse signal on a 1C04 TDA2320 microcircuit. From the output of this microcircuit, pulses are sent to the input of the sensor board.
The 1C1 microcircuit of this board performs functions similar to the KR1506HL2 microcircuit. with the difference that in addition to the circuit for decoding the signal from the remote control and generating control signals, it contains a tuning voltage driver and ROM for pre-tuning to channels. This eliminates the need for variable tuning resistors. The tuning voltage is generated from a 33V voltage supplied from the main board by a driver on transistors Q1,Q2,Q6. The control signal comes to it from pin 5 of the 1C1 chip. Band switching is carried out by switches on transistors Q3 - Q4, which turn on the corresponding stages of the RF tuner (all-wave selector) located on the main board.
The shutdown signal from pin 26 of the 1C1 microcircuit is supplied to the switch on transistor Q8, in the collector circuit of which the electromagnetic relay of the RL701 switch, located on the secam/pal transcoder board, is switched on. The control module supply voltage stabilizer is also located there, on transistor Q701. All basic adjustments without a remote control can be made using the adjustment board, on which adjustment resistors are located, connected to the nodes of the main board and buttons that form the code of the desired command in the 1C1 chip. The power-on signal, when using the TV switch, is transmitted to the 1C1 chip using the key on Q18; the third group of the power switch is used to supply this signal.
Schematic diagram of the main board. The intermediate frequency voltage from tuner T1 is supplied to the preliminary amplifier on transistor Q171, from the collector of which, through filter Z201, to the input of the intermediate frequency amplifier of the 1C101 TDA7520 microcircuit. This microcircuit contains an UPCH, a video detector, an APG and AGC system, an intermediate frequency amplifier and a sound detector. Circuit L104 operates in a video detector.
Resistor VR101 can be used to set the AGC depth. From the output of the video detector, through the emitter repeater on Q201, the complex video signal goes to connector P201 and from there to the interface module board. The video signal in the interface board is supplied to pin 3 of the TEA2014 chip. When operating from a radio channel, the video signal from pin 6 of the TEA2014 IC goes to the pre-amplifier at Q4 (Fig. 4) and from its emitter to the fourth pin of connector P201. From it, the video signal is sent to the synchronization circuit on the IC 1S401 TDA2579 and to the input of the sekai/pal transcoder through the P202 connector lower in the diagram.
The transcoder is based on the TDA3592A chip. The video signal is fed to the input circuit "flare" SL01 and from it to the pin. 3 ICs and through the SQL1 delay line to the pin. 16. The input circuit selects the SECAM color signal, and the amplified PTsTS signal with a fixed black level is output from pin 15 of the IC to the P202 circuit and from it to the base of the Q202 transistor of the main board. In this case, the SECAM/non-SEKAM switch is in such a position that the signal on the pin. 14 IC is not received. The SECAM chrominance signal, after formation, is sent to two SL04 demodulators.
One of them demodulates the chrominance signal, and the other extracts the recognition signal, which is fed to the half-line detector of the switch control system. The chrominance demodulator generates alternating lines from line to line, and inverted R-U and inverted V-U signals appear at its two outputs. As a result, both components have a positive polarity and ratio as when receiving a PAL signal. The artificial black level generator introduces clamp pulses into the demodulator, which create pads that coincide with the black levels.
A commutator controlled by half-line frequency pulses separates the signals, and the following mixer and level fixation device add and equalize them. The result is a common signal with alternating components R-U and V-U, to the reference frequency generator through the pin. 8 the quartz resonator SX01 is connected, and on pin. 9, a pseudo-PAL color signal with flashes is generated, and the phases of the flash signal on the line R-U = O, and on the B-U = 90 degrees. From the delay node on SDL2, the direct and delayed signals are sent to the pin. 11 and 12 ICs. By adding these signals at the output of the PAL matrix located in the microcircuit, a PAL color signal is formed, which, through the open pin 14 of the IC, is sent to connector P202 and from it to the main board, where it is processed as a PAL color signal. When receiving a PAL signal, the identification demodulator selects pulses of alternating polarity from line to line, which are compared in the half-line frequency detector with the pulses generated by the trigger. When the trigger is phased correctly, negative pulses appear at the detector output, discharging capacitor SC04. When the voltage on the neck drops below 6.5 V, the PAL sodium is turned on and the PAL chrominance signal is sent to the pin. 14 IC.
From the output of the video signal detector, the audio IF voltage is supplied to the first UPCH stage on transistor Q131. From the output of this stage, the signal goes to the IF frequency conversion circuit, which allows, regardless of which IF in this case is -5.5 MHz or 6.5 MHz, to have an output frequency of 6.5 MHz. The frequency mixer is made on transistor Q672, and the local oscillator is made on Q673. From the output of the PFC converter, through two series-connected filters Z132 and Z133, the signal is supplied to the frequency detector of the 1C101 microcircuit. Filter Z133 is included as a phase-shifting circuit in the FM detector.
From the output of the preliminary ultrasonic frequency, voltage 34 is supplied to the input of the power amplifier on the 1S601 - microcircuit. The signal from the Audio interface board is supplied to pin 3 of the IC 1S101. The volume control signal from the control module is supplied through connector P105 of the main board to the pin. 29 1С101. From the output of the transcoder, the luminance-U and chrominance-C signals are supplied through the lower H2U2 connector to the video signal processing path located on the main board. The brightness signal passes through the delay line DL2U1 and through the capacitor C514 enters the input of the brightness signal amplifier 1C5U1 through its eighth pin. The signal swing here is 0.45 V. Black is fixed at the amplifier output. Then follows a cascade in which during the first three lines after the vertical damping pulse, the brightness signal is extinguished and the reference black level signal is introduced.
This operation is necessary to organize the operation of the automatic white balance system, in order to obtain a certain ratio of the measuring and black levels when measuring currents. The resulting brightness signal is sent to the matrices of primary colors, which also receive color-difference signals. The color signal through pin 4 of the 1C501 is supplied to the adjustable amplifier of the AGC system. The signal swing at this input is 0.4 V. This is followed by a saturation control stage. The regulation voltage from the control board through connector P251 is supplied to the fifth pin of 1C501. The gate amplifier included further provides amplification of the chrominance signal and does not amplify the color synchronization signal, which is necessary to increase the difference between the voltage of the chrominance signal and flashes, to reduce interference due to reflection of flashes in the delay line.
From the 28th pin of 1C501, the color signal is supplied to the delay line, a matrix in which L5C2, VR501, R501, C507, R509 are sensed, with the help of which the sum and difference of the direct and delayed signals is formed to receive signals EU and EU^ these signals through the pins 22 and 23 to synchronous detectors V-U and R-U. These detectors also receive double signals from the reference oscillator, the frequency of which is stabilized by the X501 resonator. From the detectors, signals are sent to the matrix, and the brightness signal is also sent there. To adjust the brightness, a constant control voltage from the adjustment board is supplied to the pin via connector P251. 11 1С501. When receiving a black-and-white image, a voltage of 2V is set at pin 2 of the 1C501; it increases if there is a color signal to 4.5V if the PAL trigger operates in the correct phase.
If the phase is incorrect, this voltage drops to 1.5V, after which the corrector moves the trigger to the correct phase, and the voltage rises to 4.5V. This voltage is used to turn the color channel on and off. The contrast is adjusted by changing the voltage at pin 6 of the 1C501 within 2 - 4 V, and the gain of the brightness channel changes. From the output of the matrix, signals of primary colors are supplied to the preliminary video amplifiers, and from pins 13, 15 and 17 of the 1C501 to the kinescope board on which the output video amplifiers are mounted. White is preset using resistors VB901 and VR902. The 1C401 microcircuit contains a synchronization unit, which, in addition to functions similar to the domestic K174XA11 microcircuit, contains master generators for horizontal and vertical scans.
The video signal from the interface board, through capacitor C208 and the normalizing circuit R3C1, R302, R306, C305, is supplied to the input of the amplifier-limiter of the microcircuit (pin 5). External elements of the sync pulse selector R305, R304, C303, C304. Through pin 15, a horizontal frequency regulator - VR401 - is connected to the master horizontal oscillator. Horizontal pulses from pin 11 1С401 are fed to the horizontal scanning pre-amplifier at 0401. This amplifier increases the voltage of the horizontal pulses to a level sufficient to create a control current in the output stage circuit at 0402. The output stage is loaded by an H-Dy deflection coil connected via connector P45Z.
The image phasing is set by resistor VR402. In the beam current limiting system, transistor 251 operates, which makes corrections to the brightness and contrast levels set using the regulators. In addition to generating a fork-shaped voltage for the horizontal coils of the deflection system and constant voltages for the operation of the kinescope, the output stage generates constant voltages to power the radio channel and color chips, vertical scanning, and tuner tuning voltage. The 12 V voltage for powering the color radio channel is obtained from the alternating voltage taken from pin 3 of the FBT line transformer. This voltage is rectified by the D403 diode and stabilized by the 1C701 integrated stabilizer.
The voltage for powering the vertical scan is obtained by rectifying the alternating voltage from output 2 of the horizontal transformer. The voltage to power the output video amplifiers is generated from the alternating voltage taken from terminal 7 of the transformer. To power the tuner varicaps, a voltage of 33V is used, which is crushed from the zener diode D405, which is part of the stabilized voltage rectifier coming from pin 10 of the FBT transformer.
The frame scanning unit is made on a 1C301 microcircuit. The master oscillator is part of the 1C401 microcircuit, the frame rate is set by adjusting the resistor VR302, and the size is VR301. Pulses from the generator arrive at pins 1 and 3 of the 1C301. Reverse pulses are removed from the seventh pin of this microcircuit. The V-DY deflection coils are connected directly to the output stage of the microcircuit through pin 5. The S/W301 switch is used to center the image vertically. The TV's power supply is made using a pulse circuit, similar to the circuits of domestic TVs of the USCT type.
The mains voltage is pre-rectified by the BD801 rectifier, and then supplied to a pulse generator with a powerful key stage and a T601 transition transformer, which provides the necessary voltage. The output voltages are set by changing the position of the VR801 slider. For TV variants with different supply voltage ranges, the sections of the circuit marked with the letters “A” and “B”, depicted in the form of rectangles, differ.
Main technical characteristics
Received television systems: PAL/SECAM/NTSC, B/G, D/K, I, M.
Received frequency range: 45-169 MHz; 175-870 MHz.
Power supply: alternating voltage 100…270 V with a frequency of 50/60 Hz.
Setting: 100 programs, automatic or manual search.
On-screen menu: multilingual, including Russian.
Sound: MONO, stereo (from low-frequency input), stereo from broadcast (A2 NICAM).
Rated output sound power 2´8 W.
External connectors:
Additional features: the presence of sleep and on/off timers, there are child lock and “Eye” modes (dynamically changing image parameters depending on external lighting conditions). Installation of a teletext card is provided.
Power consumption from the network:
Electrical circuit diagram
The basis of the TV design is the chassis on which the TV components are located. The chassis is a horizontal board with elements of a power supply, scanners, RF and audio paths. As options, teletext and stereo sound modules (NICAM standard) can be installed on the chassis.
Let's consider the principle of operation of the TV according to the electrical circuit diagram shown in Fig. 3.1—3.3.
Video signal processing path
The broadcast television signal is supplied to the antenna input of the tuner TU101 (see Fig. 3.1).
The tuner used in the above types of TVs is digital. It contains: a digital control circuit, a frequency synthesizer, analog circuits (radio frequency amplifiers, mixers, amplifiers). The tuner is controlled by the IC01 microcontroller via the I2C digital bus.
Rice. 3.1. Schematic diagram of the MC-84A chassis
The analog and digital parts of the tuner are powered by +5 V (pin 6, 7 TV101). The +33 V voltage required to generate the tuning voltage is supplied to the pin. 9 tuners. This voltage is generated from the pin. 7 line transformer T701 and then goes through a rectifier (D743, C748) and a stabilizer (ZD102) to the tuner.
The I2C bus carries out: subband selection, tuning to television stations, and also provides APCG functions. The AGC voltage generation circuit (AGC) is located in IC501. The AGC voltage level, which is generated by the circuit included in IC501, comes from the pin. 54 microcircuits per pin. 1 tuner and is determined by the amplitude of the IF signal coming from the tuner.
The IF signal generated by the tuner is supplied to the preliminary amplifier (Q120) and then, through the bandpass filter Z101, the common-mode IF signal is supplied to the pin. 48, 49 IC501 chips. This multifunctional microcircuit performs the functions of UPCHI, UPChZ, synchroprocessor, multisystem color signal decoder and video processor.
The following TV models are produced based on the MS-994A chassis: CA-14/20/21 F89W, CA-14/20/21 F89X, CF-2O/21 D79, CF-2O/21 F39, CF-14/20/21 F69X, CF-14/20/21 F89, CF-14/20/21 F89W, CF-14/20/21 F89X. The main technical characteristics of these models are presented in table. 1.
Structurally, the chassis consists of a main board, a kinescope board, an “EYE” board (see Table 1) and a teletext module. The last two nodes are installed optionally. The main feature of the new chassis is the use of a multifunctional chip IC501 type TB1238AN from TOSHIBA, containing an amplifier, video detector, audio demodulator, video processor, synchro processor and I 2 C interface circuit. Its use has significantly simplified the chassis circuitry, which, in turn, has led to increased reliability of televisions.
Table 1. Main technical characteristics of LG TVs based on the MS-994A chassis
| Characteristic | Description |
|---|---|
| Screen diagonal, inch | 14, 20, 21 |
| Color television systems | PAL, SECAM, NTSC 4.43 (NTSC 3.58 - from LF input) |
| Television standards | D/K, B/G, I, M |
| Received frequency range, MHz | VHF-L: 46.25...168.25 VHF-H: 172.25...463.25 UHF: 471.25...863.25 |
| Number of memorized programs | 100 |
| Additional functions | EYE (automatic adjustment of image parameters depending on lighting); on/off timer; sleep timer; child lock; switching image format (Standard, Wide, Zoom); “camera” mode (not on all models) |
| Nutrition | AC mains 100...270 V, 50 Hz |
| Power consumption, W | up to 95 |
| Sound | Monophonic |
| Output power of the audio channel, W | 5 |
| Antenna input impedance, Ohm | 75, asymmetrical |
The chassis control system is built on a microcontroller (MC) IC01 type MC37221 from MITSUBISHI, working in tandem with a non-volatile memory chip IC02 type 24C04. To exchange data between chips and transmit commands to the IC501 chip, the MK uses the I 2 C digital interface.
A special feature of the new chassis is the presence of an interface for a video camera, which allows you to use the TV, in particular, as a monitor for a video surveillance system.
In table Figure 2 shows the parameters of replaceable elements depending on the diagonal of the kinescope screen.
Table 2. Parameters of replaceable elements depending on the diagonal of the kinescope screen
| Position designation | Denominations and types of elements | ||
|---|---|---|---|
| Kinescope 14" | Kinescope 20" | Kinescope 21" | |
| FR401, Ohm | 2,4 | 5,4 | 1,4 |
| IC804 | SE110N | SE110N | SE115 |
| TN801 | 163-054F | 163-012С | 163-О12С |
| R303, Ohm | 5,6 | 4,7 | 3,9 |
| R304, Ohm | 5,6 | 4,7 | 3,9 |
| R309, Ohm | 5,1 | 5,1 | 1,2 |
| R311, Ohm | 1,5 | 1.5 | 4,7 |
| R405, Ohm | 82 | 47 | 47 |
| R407, kOhm | 12 | 12 | 10 |
| R410, kOhm | 130 | 100 | 100 |
| R905, Ohm | 390 | 330 | 330 |
| R913, Ohm | 33 | 39 | 27 |
| R915, Ohm | 390 | 330 | 330 |
| R922, Ohm | 390 | 330 | 330 |
| R924, Ohm | 470 | 270 | 270 |
| S402, pf | 180 | 180 | 390 |
| S412, uF | 0,39 | 0,33 | 0,36 |
| S414, pf | 7300 | 7300 | 7300 |
| S902, pf | 330 | 560 | 560 |
| S904, pF | 470 | 330 | 330 |
| S907, pf | 270 | 560 | 560 |
Let's consider the operation of the main chassis components and the audio and video signal paths, as well as the main elements of their processing.
The power supply unit (PSU) generates stabilized voltages +115 (V+), +20 (S-VCC), +14, +12, +9 and +5 V (ST-5V) to power chassis components in operating and standby modes. It is built according to the circuit of a quasi-resonant flyback converter on an IC803 chip of the STR-F6707 type from SANKEN. IC803 includes: a master oscillator, trigger circuits, overload, overvoltage and overheat protection, as well as an output stage based on a powerful bipolar transistor. The microcircuit turns on when there is voltage at the pin. 4 is about 8.5 V, and turns off at a voltage of 5 V and consumes a current in operating mode equal to 30 mA, and in standby mode - 200 μA. Circuit R809 R810 generates the triggering voltage, and the exchange. 1-2 T802 and rectifier on elements D806, C801 - supply voltage in operating mode. The output voltages are stabilized by the feedback circuit IC804 IC801, the input of which (pin 11C804) is connected to the B+ bus, and the output is connected to the input of the error signal amplifier of the controller IC803 (pin 1). To control the current limit, the voltage drop is removed through the power switch of the transmitter (R805) and applied to the pin. 11C803 (protection level about -0.9...-1.2 V). Using transistor switches Q805-Q807 and optocoupler IC802 MK with a signal from the pin. 5 switches the power supply to standby mode. In this case, the converter operates at the minimum operating frequency.
The circuit based on elements R807, C831, Q831, Q832 generates an ABNORMAL alarm signal on the MK (pin 6) in the event of malfunctions in the output circuits of the B+ bus or in the horizontal scanning circuit. Secondary voltages +5 and +9 V are formed by integrated stabilizers IC805 and IC844, the latter being controlled. The IC844 microcircuit is controlled by the MK ON/OFF signal (pin 5).
The television radio signal from the antenna input is supplied to the input of the tuner TU101, which is controlled by the MK (pin 31, 33 IC01) via the I2C interface (pin 4, 5 TU101). The tuner is powered by a voltage of 5 V (pin 7). The output signal of the tuner (pin 11) with an IF equal to 38 MHz, through a bandpass filter Z101, which forms the frequency response of the IF path, is fed to the input of the IF - pin. 6 and 7 IC501 chips. Here are its main functions:
The pin assignments of the TB1238AN microcircuit are presented in table. 3.
Table 3. Pin assignments of the TB1238AN chip
| Pin number | Signal | Description |
|---|---|---|
| 1 | DE-EMP | audio signal output to attenuator |
| 2 | AUDIO-OUT | Audio output |
| 3 | IFVCC | Analog part supply voltage 9 V |
| 4 | AFT OUT | AFC signal output |
| 5 | ID GND | General |
| 6 | IF IN | IF signal input |
| 7 | IF IN | IF signal input |
| 8 | RF AGC | AGC voltage for tuner |
| 9 | IF AGC | AGC voltage for amplifier |
| 10 | APC FILTER | Automatic Image Adjustment Filter |
| 11 | X-TAL | Quartz crystal 4.43 MHz |
| 12 | Y/C GND | General channels of brightness and chrominance |
| 13 | Ys/Ym | HALF TONE mode control input |
| 14 | OSD R | OSD signal input R |
| 15 | OSD G | OSD signal input G |
| 16 | OSD B | OSD signal input B |
| 17 | RGB VCC | Video processor supply voltage 9 V |
| 18 | R OUT | R signal output |
| 19 | G OUT | G signal output |
| 20 | B OUT | Signal output B |
| 21 | ABCL | Input of brightness control and beam current limiting circuits |
| 22 | V RAMP | Vertical scan GPN capacitor |
| 23 | VNFB | Vertical scan OX pulse input |
| 24 | V OUT | Vertical ramp voltage output |
| 25 | V AGC | Vertical scan AGC filter |
| 26 | SCL | I 2 C interface synchronization bus |
| 27 | S.D.A. | I 2 C interface data bus |
| 28 | H. VCC | Horizontal scan oscillator supply voltage 9 V |
| 29 | ID/SW OUT | SECAM signal switching output |
| 30 | FBP IN | Login SIOH |
| 31 | SYNC OUT | Sync output |
| 32 | H.OUT | Line scan trigger output |
| 33 | DEF. GND | General |
| 34 | SCP OUT | SCP Dual Level Gating Output |
| 35 | VIDEO SW | CVBS video output for SECAM decoder |
| 36 | DIG VDD | Power supply for the digital part of the circuit (5 V) |
| 37 | SECAM B-Y | SECAM B-Y signal input |
| 38 | SECAM R-Y | SECAM R-Y signal input |
| 39 | Y-IN | Brightness input Y |
| 40 | H.AFC | AFC filter 1 |
| 41 | EXT YIN | Video switcher input 1 |
| 42 | DIG. GND | General digital part of the circuit |
| 43 | TV IN | Video switcher input 2 |
| 44 | BLACK-DET | Black Enhancement Circuit Filter |
| 45 | With IN | External chrominance input |
| 46 | Y/C VCC | Video processor supply voltage 5 V |
| 47 | DET OUT | Video detector output |
| 48 | LOOP FILTER | Connecting the AGC filter |
| 49 | GND | General VCO |
| 50 | VCO | VCO reference circuit |
| 51 | VCO | VCO reference circuit |
| 52 | VCC | Supply voltage 9 V VCO |
| 53 | LIM IN | IF signal input |
| 54 | RIPPLE FILTER | Anti-aliasing filter |
| 55 | EXT AUDIO IN | External audio input |
| 56 | FM DC NF | Audio power filter |
The video processor switch input (pin 14-16 IC501) can receive OSD-R, G, B, teletext signals TXT-R/G/B or external SCART-R/G/B signals. The selection of the required signals is carried out by the IC751 switch, controlled by the FB-ID signals (pin 39 IC01), TXT-FB (pin 8 P701B) or SCART-FB (pin 16 PJ201). Output video signals of primary colors with pin. 18,19, 20 IC501 via pin. 2, 4 and b connectors P901B are supplied to the transistors of the output video amplifiers Q901-Q903, which are powered by a voltage of 180 V from the horizontal scanning circuit. In addition, through contact 1 P901V a bias voltage of 12 V is supplied to the video amplifiers, which determines the operating points of the transistors. There are no adjusting elements of video amplifiers in the circuit because all adjustments are performed by the IC501 video processor in service mode using the MK via the I 2 C interface.
The main part of the audio path is located in the IC501 chip. To isolate audio signals of different standards, use the IC151 switch with filters F151-F154, controlled by MK signals: SO, S1 and M4.5 (pin 38, 39, 14). The IF signal from the output of the video detector (pin 47 of IC501) is fed through buffer Q507 to the inputs of filters F151-F154 connected to switch IC151. Output signal FCZ with pin. 3 IC151 is supplied to the demodulator input - pin. 53 IC501. The audio output from the demodulator is amplified and fed to the INT/EXT switch (inside IC501) to select the appropriate signal. External sound signal to pin. 55 IC501 comes with SCART or Cinch connectors. The audio signal source selected by the microcontroller IC01 via the I 2 C interface is removed from the pin. 2 IC501 and is fed to the input of the audio frequency power amplifier (UMZCH) - pin. 5 chips IC601 type TDA7253, which is a single-channel push-pull class AB amplifier with short-circuit protection and a MUTE sound blocking input (pin 3). From its output (pin 8), the signal goes through the isolation capacitor C605 and connector P601 to the dynamic head. The UMZCH is powered by a 20 V power supply (S-VCC).
A teletext module can be installed on the MS-994A chassis, which is connected via connectors P701B, P702B. The module is based on an IC701 chip of the SAA5281 type, which has 8 Kx8 RAM for 8 teletext pages. It is designed to work with the 625-line WST (World System Teletext) standard. In addition, the chip decodes VPT (Video Recorder Programming) signals. It is controlled by the MK via the I2C interface (pin 24, 25). To operate IC701 on its pin. 9, a TXT-CVBS video signal is received from IC501 (pin 35). At the outputs of the microcircuit, teletext signals R, G, B (pin 16, 17, 18) and a blanking signal (strobe) TXT-FB (pin 20) are generated, which are fed to the switch IC751, and from it to the video processor IC501.
To power the teletext module on pin. 3 P701V is supplied with 9 V voltage from the power supply. The IC701 chip is powered by a voltage of 5 V from the stabilizer IC702.
Horizontal scanning is built according to a conventional two-stage circuit (transistors Q401, Q402) with serial power supply to the output stage. Transistor Q401 is supplied with a voltage of 14 V, and Q402 is supplied with a voltage of +115 V (V+) from the power supply. The output transistor has an internal snubber diode. The T402 line transformer generates the supply voltage for the kinescope, vertical scanning (24 V) and output video amplifiers (180 V). All secondary circuits of T402 are protected from overload by breaking resistors FR301, FR401 and FR501.
A voltage is generated at capacitor C418 that is inversely proportional to the current of the kinescope beams. The ABL (OTL) signal from the output of the shaper is sent to the pin. 21IC501 to control beam dimming and current limiting circuits.
The vertical scanning output stage is implemented on an IC301 chip of the LA7833 type from SANYO. Sawtooth vertical pulses are supplied to the input of the microcircuit (pin 4) from pin. 24 IC501. The V-DY OS frame coils are connected to the output of the microcircuit (pin 2). To control and stabilize the vertical size, the V-NFB feedback signal is removed from the amplifier output and applied to the pin. 23 IC501.
As already noted, the IC301 microcircuit is powered by a voltage of 24 V (pin 6) from the horizontal scanning circuit.
To synchronize the OSD circuit, OX pulses of the horizontal (pin 10 T402) and vertical (pin 7 IC301) scans are fed through inverters Q01, Q02 to the MK (pins 1 and 2).
MK IC01 performs the function of controlling all chassis components. The operation of the MK is ensured by the quartz resonator X01 (pin 19, 20), the reset circuit IC03 and the non-volatile memory IC02. The purpose of the microcircuit pins is presented in table. 4.
Table 4. Pin assignments of IC01 chip
| Pin number | Signal | Purpose |
|---|---|---|
| 1 | H-SYNC | Horizontal sync input |
| 2 | V-SYNC | Vertical sync input |
| 3 | LED | LED output |
| 4 | CC/AV-ID | Camera/LF input source identification input |
| 5 | POWER | Power supply control output |
| 6 | ABS | Alarm input |
| 7 | MNT-CTL | Switching sound to SCART (TV/AV) |
| 8 | DEGAUSE | Output for turning on kinescope demagnetization |
| 9 | EYE | Light sensor signal input |
| 10 | IR-IN | Signal input from photodetector |
| 11 | SD-IN | Video signal identification input |
| 12 | TURBO | Tuner tuning mode switch output |
| 13 | TBS-SW | Tuner AGC time constant switch output |
| 14 | 4.5M | Standard M |
| 15 | S-MUTE | Sound blocking output (not used) |
| 16,18,21 | GND | General |
| 17 | FS | Service mode switch input |
| 19 | X-IN | Quartz crystal 8 MHz |
| 20 | X-OUT | Quartz crystal 8 MHz |
| 22 | VCC | Supply voltage +5 V |
| 23 | 0SC2 | Generator output 1 (not used) |
| 24 | 0SC1 | Generator input 1 (not used) |
| 25 | RESET | Reset input |
| 26 | A.F.T. | Tuner fine tuning control input |
| 27 | A.G.C. | AGC voltage input |
| 28 | F8-ID | Blanking pulse input from SCART |
| 29 | KEY1 | Keyboard Scan Input 1 |
| 30 | KEY2 | Input 2 keyboard scan |
| 31 | SDA1 | I2C interface data bus |
| 32 | CCTV-CTL | TV/Camera Mode Switch Output |
| 33 | SCL1 | PC interface synchronization bus |
| 34 | CCTV-ID | CCTV signal identification input |
| 35 | Ym | Switch output "1/2 image brightness" |
| 36 | MELODY | Audio information signal output |
| 37 | 51 | TV standard switch output 1 |
| 38 | SO | Output 2 TV standard switch |
| 39 | FB | OSD blanking pulse output |
| 40-42 | B-G-R | Video outputs of OSD circuit |
As with any modern television receiver, after repair or replacement of adjustment elements of the RF path, video processor and other components on the MS-994A chassis, they are performed in service mode. To work in this mode, you must have a remote control with teletext control buttons. Before making adjustments, turn on the TV, apply the “Test pattern” signal to its antenna input and warm it up for 15...20 minutes.
To enter the service mode, simultaneously press the "OK" buttons on the remote control and on the front panel of the TV, holding them down until a list of adjustable parameters appears on the screen (Fig. 1). The last line "LINE SVC 0" shows the menu number, and there are five in total (LINE SVC 0-4).
Rice. 1. List of adjustable parameters in service mode
The required parameter is selected using the up-down joystick buttons, and its value is adjusted using the right-left buttons. To save the new parameter value, click the "OK" button. To exit the service mode, switch the TV to standby mode using the "Power" remote control button. Let's consider the sequence of adjustments of the main parameters on the MS-994A chassis.
This adjustment is required after replacing the tuner, as well as when significant noise (interference) appears in the image.
The accelerating voltage is usually adjusted after replacing the kinescope or after repairing the horizontal scanning circuit.
This operation must be performed after adjusting the accelerating voltage.
Factory settings of parameters are given in table. 5.
Table 5. Factory default white balance settings
| Parameter | Factory values |
|---|---|
| R.C. | 125 |
| G.C. | 140 |
| Sun | 125 |
| GG | 58 |
| B.G. | 65 |
This operation is performed in the same cases as the previous one, as well as when focusing deteriorates. Turn on the TV, apply a “Grid” or “Test Pattern” signal to its antenna input and warm it up for 15...20 minutes. Then, use the Focus regulator on the horizontal transformer to achieve the best focusing of the image.
This adjustment is made as needed.
Setting options
Adjusting options is necessary in order to configure a specific TV model. Options are set in the "OPTION 1" and "OPTION 2" menus.
Table 6
| Option | Code | Function |
|---|---|---|
| SHI SYSTEM | 0 | BG standard only (CA- models) |
| 1 | BG + TAI DUAL (Asia) | |
| 2 | BG + 1 + DK (without NTSC 3.58, models CF-, CZ-) | |
| 3 | BG + DK + M (with NTSC 3.58, models ST-, CD-) | |
| CCTV | 0 | Without CCTV |
| 1 | With CCTV system | |
| SCART | 0 | Phone Jack or Carnera-in Jack only |
| 1 | There is a top Scart Jack connector | |
| 4 KEY | 0 | 6 buttons on the front panel (MENU, OK, VOL-, VOL+, PR-, PR+) |
| 1 | 4 buttons on the front panel (TV/AV, ROTATE, PR-, PR+) | |
| EYE | 0 | Without Eye system |
| 1 | With Eye system | |
| TOP | 0 | Teletext is prohibited |
| 1 | Teletext allowed | |
| H-TONE | 0 | OSD on blue background |
| 1 | Halftone background for OSD |
Options and their possible values are given in table. 6 and 7.
Table 7
| Option | Code | Function | Microcontroller version |
|---|---|---|---|
| LANG | 00 | Multilingual support | - |
| 01 | English only | ||
| 10 | Two languages | ||
| LANG-INDEX | 0 | English | LG8993-27A/B |
| 1 | Former USSR countries | ||
| 2 | Chinese | ||
| 3 | Romanian | ||
| 4 | Polish | ||
| 0 | English | LG8993-28A | |
| 1 | French | ||
| 2 | Indian | ||
| 3 | Arab | ||
| 4 | Urdu | ||
| 5 | Persian | ||
| 0 | English | LG8993-29A | |
| 1 | Indonesian | ||
| 2 | Malay | ||
| 3 | Vietnamese | ||
| 4 | Thai | ||
| CURVE | 0 | Fast volume rise | - |
| 1 | Slow rise in volume | ||
| TBS | 0 | TBS function disabled | - |
| 1 | TBS function enabled | ||
| HOTEL | 0 | Function disabled | - |
| 1 | Function enabled |
The TV does not turn on, the "POWER" indicator does not light, the mains fuse F801 blows
Disconnect the TV from the network and use an ohmmeter to check for short circuits the elements of the demagnetization circuit, line filter, rectifier: TN801, TN802, C806-C810, VD801, T801, RT801, RT802, DB801. If there is no short circuit in these circuits, then use an ohmmeter to check the power transistor for a short circuit (pins 2 and 3 of IC803). If the indicated elements are in good condition, the T802 transformer is unsoldered and checked using one of the well-known methods.
The TV does not turn on, the "POWER" indicator does not light, the mains fuse F801 is working
Turn on the TV using the power switch SW801 and measure the voltage +300 8 on the pin. 3 IC803. If the voltage is zero, then check the elements of the following circuit for an open: F801, SW801, T801, R811, DB801, pin. 8-5 T802, FB803, pin. 3 IC803. If the voltage is 300 V at pin. 3 is present, but the converter does not work (there are no pulses with a swing of about 500 V on pin 3 of IC803), then check the external elements of the microcircuit that provide its power in the startup and operating modes (see description).
If the converter is working (there are pulses on pin 3 of IC803), check the 5 V stabilizer (IC805). If it is serviceable, then check the MK and its external elements (see description and Table 4).
The "POWER" indicator is on, the TV is in standby mode and does not switch to operating mode
First of all, check the ON/OFF signal (pin 5 IC01). If the signal is high (i.e. the TV is in standby mode), the streaming overload protection of channel B+ of the power supply may have triggered.
In this case, the ABNORMAL signal is output. 5 IC01 will be active (low level). Turn off the TV and determine the cause of channel B+ overload. If the protection signal is passive, the MK itself may be faulty or the IC02 memory has failed. The microcircuit is rewritten and, if the TV still does not turn on, the MK is replaced. If the ON/OFF signal (pin 5 IC01) is low, the Q807 key must be closed and the 9 V stabilizer (IC844) must be turned on.
There is no raster and sound, the power supply is working
Perhaps one of the voltages on the kinescope board and the kinescope itself is missing: HV, USCREEN, UHEATER. 180 V. Check the presence of the specified voltages, determine what is missing and eliminate the cause. If there is no high voltage (no characteristic crackling sound when turning the TV on and off), then most likely the reason is in the horizontal scan circuit. Check for the presence of trigger pulses on the pin. 32 IC501, their input to the preliminary stage on transistor Q401 and the operation of the output stage on transistor Q402 (there should be pulses of positive polarity at the collector with a swing of about 1000 V). If the output stage does not work, disconnect the TV from the network and check all its external elements. If there are pulses, but there is no high voltage, the reason is in the line transformer T402.
There is a raster, but there is no sound and image
First, check the IF path and video processor (IC501 chip). They control the power supply of the microcircuit (see Table 3). If there is no supply voltage of 5 V (pin 46), check the stabilizer IC505. If the power supply is normal, apply a test signal with a frequency of 38 MHz with a level of 65 dB to the input of the IF path (pin 11 of the TU101 tuner) and control the passage of the signal along the path (see description and oscillations 1, 3-5). Identify and replace faulty elements. If there is no test generator, you can use a VCR or video camera connected to the appropriate inputs as a signal source, but in this case only the video processor is tested.
No color image in SECAM color system
Most likely, the IC502 chip or its external elements are faulty. Set the saturation control to the maximum level position. Check the power supply of the microcircuit (5 V on pins 9 and 18. If there is no voltage, check the stabilizer on elements ZD504, R531), the presence of a video signal on pin. 13 and 15 IC502, gating pulses on the pin. 17, all external capacitors. If the elements are in good condition, replace the microcircuit.
The TV only works through the low-frequency input
Check the power supply of tuner A101 (33 and 5 V). Then a test signal is supplied to the antenna input of the tuner from the generator, the auto-tuning mode is turned on and the corresponding control signals are checked at the tuner terminals (see description). If there are signals, but the IF output signal (swing 0.25...0.5 V) is missing, replace the tuner.
No sound
Check the power supply of the IC601 microcircuit (20 V on pin 9) and the absence of a blocking signal (high potential on pin 3), the serviceability of the dynamic head and the presence of a contact in the P601 connector. Then they touch the pin with a metal object (for example, tweezers). 5 IC601. If a background appears in the dynamic head, then the UMZCH is working. Otherwise, replace the microcircuit.
There is no sound when receiving TV programs
Check the presence and passage of the sound signal along the following circuit: pin. 47 IC501, Q507, Q151, F151-F154, pin. 1, 2, 4, 5 IC151, pin. 3 IC151, pin. 53 IC501, pin. 2 IC501. Identify and replace the faulty path element.
No sound or image when working through the LF input
Check the corresponding paths.
Video path: PJ201, C251, pin. 7, 8 IC251, pin. 41IC501.
Sound path: PJ201, C227, Q221, pin. 10.11 IC251, C257, pin. 55 IC501.
The TV does not respond to remote control commands
The remote control is faulty. First, install known good batteries in the remote control. To check, use an IR photodiode, for example, FD-8K, connect its leads to the input of the oscilloscope, point the remote control at the photodiode and press one of the remote control buttons. The oscilloscope screen should contain bursts of pulses with an amplitude of about 0.5 V. If they are not there, check the serviceability of the remote control circuit elements: microcircuit, resonator, output transistor and LED.
If the remote control is working, press one of the remote control buttons and check for the presence of a signal with an amplitude of 4...4.5 V on the pin. 1 PA01. If there is no signal, then replace the photodetector. If there is a signal, the microcontroller IC01 is faulty.
The image is dominated by one of the colors, a black and white image has a color tint of the same color
As a rule, this occurs due to changes in the parameters of radio elements and the kinescope due to their aging. To resolve this, adjust the white balance in the service mode (see "Service mode").
A thin horizontal line is visible on the TV screen
Check sawtooth pulses (oscillation 9) for pin. 24 IC301. If they are not there, check capacitor C313 (oscillation 6) and all elements in the feedback circuit: C308, R314, R313, R306, R407, C301.
If sawtooth pulses on the pin. 4 IC301 is there, but the output signal is on pin. 2 is missing (signal swing is about 45...50 V), check the power supply of the microcircuit (24 V at pin 6) and the following elements: R303, R304, C311, R310, C310, V-COIL If they are working, replace the microcircuit IC301.
The vertical image size is small and cannot be adjusted in service mode
Check the elements of the voltage booster circuit D302 and C307.
Sometimes it seems to me that the work of a radio amateur repairman is similar to the work of a necromancer. We, too, have to perform complex secret rituals in order to once again breathe life into a dead creature. So today I performed another ritual over something that had recently been spoken and shown, and now stands in the center of the room like a dead pile of iron.
So, the LG CF20J50 TV does not show a single sign of life. Even the standby light does not light up. Therefore, putting on a black robe with a hood and reading a special prayer from a radio amateur - a necromancer, I begin to smoke the TV with clouds of rosin smoke (helps to expel the demon of malfunction).
As for auxiliary devices, I have a digital multimeter and a set of screwdrivers. We open the case and carefully examine the insides - no burnt tracks, no swollen electrolytes, no blackened resistors. Hope begins to glimmer for a freebie, like a blown fuse.
I call - it's a bummer. Start over. The mains wire is normal, the fuse is OK, the switch... And here is the defect. In a two-section 220V network switch (a la P2K), one section does not ring. As an experiment, we shorten it with a piece of wire and try to start the TV - it works!
Here it is, a freebie. One section of the switch simply failed. I could have stopped there (leaving the jumper), but I decided to do everything humanely. I'll try to fix it.
We unsolder the power switch from the board, lightly pressing on one edge - at the same time taking turns passing the soldering iron tip along its four contacts. Let's take it apart and look inside.
Serious design. If this one fails, it will not be easy to find a replacement. It needs to be repaired.
The problem, as expected, was a contact that had become burnt over time. Carefully clean it with fine sandpaper and put it back together - a matter of minutes.
Now you can, after checking it with a multimeter, solder it back into the TV’s printed circuit board.
We assemble, twist, put in place, and voila! The TV is like new (if you can say so about a device ten years ago). It took 25 minutes to do everything. Your congratulations and applause are on
Discuss the article LG TV REPAIR
Hello. Today we are repairing an LG 21FS2CG TV assembled on a chassis mc-059c. When voltage is applied, the TV “clicks” and does not turn on, which indicates an overload of the power supply.
Let's start the repair.
Having disassembled the TV, the first thing I decided to do was inspect the board for swollen capacitors or burnt resistors. This event did not bring any results, since all elements look normal.
The next step in determining the malfunction was checking the rectifier diodes of the power supply output. When diode vertebrae D826 the multimeter showed a resistance of 7 ohms, which indicates a short circuit on the bus 110v.
If you look at the diagram, the diode itself, or the line transistor, can cause a short circuit Q402, the collector of which receives voltage 110v. Capacitors or TDKS can also short out, which is quite rare.
Unsoldering one leg of the diode D826, I check the board again for a short circuit. Everything remained unchanged, which means that the reason is not the diode. The next element to check was the line transistor (HOT).
Having freed the legs of the transistor from the tin braid, I removed the transistor itself. This chassis has a transistor marked C6090. It turned out to be the culprit of the short circuit on the board. All legs of the transistor were closed.
As you can see, finding a faulty transistor is not difficult; a more time-consuming task is to determine what caused the breakdown of the transistor itself. HOT, since these transistors themselves burn out extremely rarely.
While the line transistor is unsoldered and there is no short circuit on the board, I decided to check the output voltage of the power supply. To do this, as a load, I solder it to the container S814 lamp 75W, and turn on the TV. The lamp turned on at half-glow, as the TV was in standby mode. Having measured the standby voltage with a multimeter, it turned out that it was 78V, which is the norm. I turn on the TV in operating mode, and the voltage rises to 113, which indicates that our power supply is working properly.
After checking the power supply, I return to the line designer. There are several main reasons why a horizontal transistor may burn out:
After checking the power supply, I decided to check the collector capacitances. In this chassis, the capacitance that directly affects the drive of the transistor is C414. In the diagram it is indicated by an exclamation mark, which means that its denomination may differ from that indicated on the diagram. Having soldered the capacitor I saw that its marking 123j, which corresponds to 12nF.
To check the capacity, I connected it to. The result was instead 12nF order 5.5nF. This loss of capacity could have caused the breakdown of the horizontal transistor.
After I discovered a faulty capacitor, I decided to put everything back in place. Instead of C6090 installed BU508DF, and instead of a burnt container 12 nF *2000v installed capacity 11 nF *1600v since there was no identical one at hand.
After the installation work was completed, I turned on the TV to the network. The TV started up and showed a normal screen scan.
After 30 minutes of operation, the radiator temperature was 57 degrees, which is a good result.
I hope that the article is useful to someone. Below, as always, I attach a diagram of the TV. If you have questions, write in the comments. Thank you for your attention.
