Schematic diagram of a kinescope TV on LG. Download diagrams for LG TVs. Well, let's repair the lg TV ourselves
Hi all!
This time we will repair TV LG on chassis MC-059C.
So, I entered TV repair LG with the following problem: the device switches on to standby mode, the standby mode indicator naturally glows red, when switching to operating mode (i.e., when turned on by the remote control), the TV turns on for a few seconds, line scanning starts (a characteristic crackling sound is heard ) And …. goes into standby mode again. When you turn it on again, everything repeats.
Well, let's produce TV repair lg with your own hands .
lg tv circuit diagram , on the MS-059S chassis, you can find and download in the “” section of this site.
The first thing that was done after disassembling the device was discharging the power capacitor (bank) in order to avoid unexpected electric shocks and all kinds of short circuits.
After this it was produced visual inspection for “swollen” capacitors, burnt components and various mechanical damage, which yielded nothing. At first glance, everything was fine.
Next, using a multimeter, the secondary power circuits were checked: diodes, zener diodes, stabilizers. Has also been checked line scan – transistor and elements in its wiring.
Then the output circuits of the line transformer were checked, which also led to nothing.
Since the device turned on briefly, it was possible to check the output voltages, which was done. The secondary power circuits turned out to be quite functional, but in the output circuits of the line transformer there was some certainty in troubleshooting this TV.
When measuring the supply voltage personnel scan It turned out that the voltage was very high - more than 35 V, although it should be within 25...27V. The radioelements of this circuit were tested: diode, limiting resistor. Since the capacitor in this circuit did not visually raise suspicions, it was decided to remove it from the board and check for loss of capacitance and high equivalent resistance (ESR). An ESR meter was used for this. The rating of the capacitor being tested was 470 µF 35V.
After measuring the parameters of this component, it was revealed that the capacitance was reduced to 150...200 μF, and the ESR resistance was more than 2 Ohms. These parameters were the cause of the overvoltage.
Since the supply voltage of the frame chip was greatly overestimated, it was logical to assume that it too had failed, which was later confirmed. The STV9326 frame chip was replaced with a new one, as was the 470uF 35V capacitor.
After all the above actions, a test turn on of the TV was performed, which turned out to be successful - the TV turned on and continued its work. Without turning off the device, a control measurement of the voltage on the power supply of the personnel chip was made. This measurement showed that this voltage is within 26...27V, i.e. as it should be.
So, the cause of the TV malfunction was the loss of capacity on the electrolyte and, as a result, it failed personnel chip .
Next, the TV was put on a “run”, which ended successfully after a day of successful operation of the device. Now all that remains is to assemble our television receiver and give it to the happy owner.
Basic specifications
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:
- front: RCA-IN, headphone output;
- rear: - RCA-IN/OUT, SCART.
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:
- 14" kinescope - 80 W;
- 20" kinescope - 90 W;
- 21" kinescope - 95 W.
Fundamental electrical 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: digital circuit controls, 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.
Design and features of the MS-994A chassis
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. Main feature The new chassis is the use of a multifunctional microcircuit 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 TVs .
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 setting image parameters depending on illumination); on/off timer; sleep timer; child lock; switching image format (Standard, Wide, Zoom); “camera” mode (not on all models) |
| Nutrition | Net alternating current 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.
power unit
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. Output voltages are stabilized by the circuit feedback 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 integral stabilizers IC805 and IC844, the latter being controlled. The IC844 microcircuit is controlled by the MK ON/OFF signal (pin 5).
Image path
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:
- generating a full color video signal (CVBS) from the IF signal;
- generation of an audio signal from the PFC signal;
- generating AGC voltage for the tuner;
- automatic detection color systems and decoding of PAL and NTSC systems;
- control of external SECAM decoder (IC502);
- extracting the brightness signal from CVBS;
- formation from color difference signals: brightness signal and primary colors (RGB);
- switching of RGB signals and on-screen menu (OSD), their amplification to the level necessary to control output video amplifiers on transistors Q901-Q903;
- extracting clock pulses from CVBS and generating horizontal scan trigger pulses and sawtooth voltage to control vertical scanning;
- receiving and processing control commands from the MK via the I 2 C interface.
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 resonator 4.43 MHz |
| 12 | Y/C GND | General channels brightness and color |
| 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 scan 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.
Sound path
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).
Teletext module
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.
Line and frame scan nodes
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).
Microcontroller
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 audio 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 |
Service mode
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.
HF AGC adjustment
This adjustment is required after replacing the tuner, as well as when significant noise (interference) appears in the image.
- Connect a voltmeter to the pin. 1 tuner TU101.
- The signal "Colored polos" is supplied to the antenna input of the TV from the television signal generator
- sy" with a level of 65 dB, turn on and configure the TV to receive this signal, and then switch it to service mode.
- Select the “AGC” parameter in the menu and by adjusting it, achieve a voltmeter reading of 2.3 V for a tuner type 6700VPV002A or 3.0 V for a tuner type 6700VPV002B. The "OK" button saves the new value of the "AGC" parameter.
Adjusting the accelerating voltage
The accelerating voltage is usually adjusted after replacing the kinescope or after repairing the horizontal scanning circuit.
- The “Color Bars” signal from the television signal generator is supplied to the antenna input of the TV.
- In service mode, select the "LINE SVC 3" menu, and in it - the "CUTOFF" parameter.
- Using the Screen regulator on the T402 transformer, we ensure that the light horizontal line is barely visible.
Adjusting White Balance
This operation must be performed after adjusting the accelerating voltage.
- A “White field” signal is supplied to the antenna input of the TV and the contrast adjustment is set to maximum, and brightness to 90% of the maximum position.
- In service mode, select the "LINE SVC 0" menu.
- By adjusting the “GG” and “BG” parameters, you achieve a “light” white balance.
- Set the brightness and contrast adjustments so that the screen barely glows, and by adjusting the “RC”, “GC” and “BC” parameters, achieve a “dark” white balance.
- If necessary, repeat the adjustment several times to achieve optimal balance.
- white.
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 |
Focus adjustment
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.
Adjusting image geometric parameters
This adjustment is made as needed.
- The same signal is supplied to the antenna input of the TV as in the previous case.
- Before making adjustments, use the "ARC" button on the remote control to select the "STANDARD" image format.
- Enter the service mode, and in it select the "UNESVC2" menu.
- Sequentially select the parameters “VL” (vertical linearity), “VS” (vertical alignment), “VA” (vertical size), “HS” (horizontal alignment), “SC” (S-correction) and adjust the geometry Images.
Setting options
Adjusting options is necessary in order to configure specific model TV. 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 |
Typical faults and solutions
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 circuit 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 at pin 3 of IC803), then check external elements microcircuits that provide power to it in 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 high level(i.e. the TV is in standby mode), the streaming overload protection of the B+ channel 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 impulses, and high voltage missing - 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 black and white image has the same color 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.
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 rectifier diodes 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. Next element to check, the line transistor has become (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 soldered off and there is no short circuit on the board, I decided to check output voltage 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:
- The supply voltage of the horizontal transistor is too high. I ruled out this reason after checking the power supply under load.
- Drooping or shorted capacitors in the collector circuit of the horizontal transistor. This reason is probably one of the most common, since these capacitors operate under heavy load, and over time they can lose their capacity, as a result of which the line transistors burn out.
- Burnt-out TDKS or shorted coil of the deflection system. This is also a common cause of HOT breakdown, especially in LG.
- TMS, drive transistor or horizontal scanning trigger sync pulse (SIZ SR). I came across it extremely rarely.
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. It is indicated on the diagram exclamation mark, which means that its value 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.