The system of control over the work units in TVs with digital control provides reliable protection devices during failure. When the occurrence of a fault, especially in power circuits (blocks and lowercase HR scan, the secondary supply voltages stabilizers, etc.), it switches the TV to standby mode, and turn it impossible. How to turn off in this case, the protection system for repair, told in published article. The author examines the work of these TVs on the example of the apparatus JVC-AV-G21T, and also gives advice on entering the service mode and methods adjustment.
A significant decline in the prices of household appliances (in US dollars) in recent years touched many TV models. To the greatest extent it relates to the most popular devices on the screens with a screen size of 37, 51 and 54 cm. Many manufacturers already in 1992, managed to bring the retail price a television picture tube having a screen size diagonal 54 cm, up to 300...350 $ without reducing their technical level and quality. You can only guess what is their true cost, but some paths significant cost reductions can be traced clearly.
As an example, consider a fairly popular TV JVC-AV-G21T (was purchased by the author in 1996). In a somewhat modernized form it continued release in 1998 (model JVC-AV-2130EE at the price of $ 345., see [1]).
Let's briefly look at the technical characteristics of the TV. Intervals the received frequencies 46,25...168,25, 175,25...463,25, 471,25...863,25 MHz overlap tuner CEEU534-803, tunable synthesizer voltage, E. ensures reception of all broadcast and cable channels (1-12, 21-60, S1-S41). Working registerdata - B, G, D, K, K1, I, color system - PAL/SECAM, and video inputs - NTSC3,58/NTSC 4,43, which are selected automatically and manually.
In addition, the device is equipped with video and audio inputs on front and rear panels and video and audio inputs-rear (RCA connectors). Setup and management possible from the front panel and remote control, are provided for quick adjustment brightness, contrast, color saturation, or hue (NTSC system), clarity and volume. Power consumption: 70 watts (maximum - 105 W) at supply voltage 90...260 V.
These parameters does not allow to relate this model to the category simple and low cost, according to the author, the firm managed JVC to ensure mainly due to the exclusion of the majority of technological operations the adjustment on the Assembly line. Previously (20 years ago) every workplace traffic controller was equipped with expensive measuring equipment and tooling. In addition, required highly qualified staff on most technological operations for adjusting and testing.
TV JVC-AV-G21T (and many other models of the company in recent years) domestic classification refers to the fifth generation, i.e. to digital TVs with microprocessor control and analog processing audio and video signals [2]. However, it has some features apparatus of the sixth generation: the majority of technological adjustment operations produced in digital form by programming non-volatile electrically reprogrammable memory EEPROM (EEPROM). In our case - IC AT24C04 (IC702).
Because with this method of adjustment is little need for the connection instrumentation control points inside the TV and tune different elements with variable parameters (inductor, trimmer resistors and capacitors), it is possible to significantly reduce production costs. In addition, adjusting multiple instances TVs, in the future you can enter the initial information in EEPROM programmer. In this case it will be necessary only to test down from the conveyor apparatus, and if the deviation of any parameter from par - only adjustment with the remote control.
A simplified block diagram of TV JVC-AV-G21T depicted in Fig. 1. It includes switching power supply on a chip STR-S6707 (IC901) SANKEN company, block horizontal discrete, block frame scanning on the IC LA7837 (IC401) SANYO, all-wave tuner CEEU534 (TU001), multi-functional processing unit of the television signal on chips М52343SP (IC201), M52325P (IC302) MITSUBISHI, U3660M-B (IC301), switch audio and video inputs on the chips LA7016 (IC251, IC651) company SANYO amplifier of sound frequency on the chip AN5265 (IC601) firm MATSUSHITA, control system and the settings on the microprocessor MM-050SP (IC701) and a number of voltage regulators and assemblies using discrete components.
(click to enlarge)
The amount of tasks we should first distinguish single-chip micro-computer М37212М4050SP (IC701) by MITSUBISHI. JVC traditionally widely uses in his video equipment microprocessors and other chips that of the company, other than a very high reliability. Spontaneous, without noticeable external causes, failure of microprocessors is a very rare, can not say about the products of some other companies. For example, the infamous television repairers microprocessors TMP47C434N - R214 (QSMQAOZTS015) and TMP47C634AN - R584 (QSMQAOZTS045) firm FUNAI has provided great value to our company selling electronic components. Unfortunately, when operating TVs widespread spontaneous failure of these BIS.
The power of the microprocessor (+5 V) provides specialized stabilizer IC703 on the chip L78LR05E-MA. It also contains a reset unit to reset microprocessor when the machine. Power circuit VDD (pin 27) microprocessor carefully untied from the penetration of noise U-shaped filter С709L701C711.
The microprocessor IC701 provides most of the functions on the operational management of all other functional blocks of the TV and control over execution of the commands. In addition, it is entrusted with the task of technological adjustments on the production stage for what the TV is built with virtually no trimming elements (coils, resistors and capacitors). From traditional hand adjustments are trimming resistors focus and the voltage at the anode the CRT A51LEC098X in the line scanning unit and the slider image size vertically in the frame scanning unit.
Digital bidirectional highway (presumably I2C, designation on the scheme - BUS I/F) microprocessor communicates with the multifunction BIS processing a television signal IC201 (signal SCL1 and SDA1 - conclusions 37 and 39 of the microprocessor) and a non-volatile storage device IC702 (scl2 generates signals and SCDA2 - of the pins 36 and 38). All of these signals are displayed on control connector CN00C that allows programming of the storage device from external computer, to connect a logic analyzer or other instrumentation for diagnostics and repairs in production and service centers.
The appointment of the remaining control outputs (conclusions) of the microprocessor as follows:
4 - signal mode vertical 50/60 Hz (goes to pin 5 chip IC401);
8 signal comprising the indication led mode OFF TIMER on the front panel;
9 - the control signal volume control in the chip IC601;
10 - signal lock sound through the circuit on common wire of pin 4 of the chip IC601 (via matching cascade);
19 - activate the operating mode of the TV with a supply voltage of +5 V on the transistor Q942 power unit (in standby mode, the transistor is closed);
20-22 signals control voltage synthesizer tuner - CLOCK, DATA, ENABLE (sync, data, resolution settings);
31 - enable signal notch filter CF124 4.5 MHz in videotrack when working with standards from M and N (filter only works when docked via video with some TV tuner, NTSC; when connecting VCR VHS or VCD players the presence or absence of filter indifferent; dock via the antenna input with NTSC equipment in a model provided);
31, 32 signals control the modes of the sound path, which makes it switching to the reception of television signals with a frequency separation of 5; 6 and 6.5 MHz (the desired mode can be selected manually with the remote control);
41 - control signal to switch audio and video inputs on the chips IC251, IC651;
50-52 signals B, G, R driver menu settings and adjustments are to the corresponding inputs of the chip IC201 (findings 25, 27, 29) channel processing television signals.
To ensure the health of the nodes of the TV and the correctness of their the functioning of the microprocessor has the following inputs (outputs): 1 and 2 for the filing of the row pulse from the winding of TDKS and personnel of pulses from the output cascade chip IC401 (through the buffer stages and resistive attenuators), and also 7 - to monitor the status of the protection system nodes of the block scan.
Since the construction of the protection device has specific features, it is advisable to consider its operation in more details on the schema fragment in Fig. 2. The key on the transistor Q581 provides tracking for three stress. In the initial state with a properly working TV it securely closed. As the voltage on the collector is absent, the level 0 on the chain NECK goes to pin 7 of the microprocessor. Controlled power supply circuit via voltage dividers, diodes, and a common resistor is connected to the base R549 transistor Q581: for a voltage of +8 In it - R594, R595, D568, and +12V - R592, R593, D567. Voltage +27 V is controlled indirectly, as a divider R550R565 through the diode D565 and personnel deflecting coil connected to the secondary the point of the output stage vertical in the chip IC401 (pin 12) voltage +V. 14
In normal condition all the diodes are closed is applied to the cathodes voltages with the corresponding divisors. With the disappearance of any of these stresses open one of the diodes and therefore the transistor through Q581 the corresponding resistor in the lower arm of the divider (connected to GND). The collector of the transistor and the conductor NECK appears a voltage of +5 V, meaning for CPU fallback mode. As a result, the pin 19 and Explorer P-ON/OFF of the microprocessor (see Fig. 1) the voltage drops to zero, transistors Q941, Q942 in the power supply is closed, the tension disappears +12V (HD-VCC), the supply unit scan, and the TV goes into standby mode (standby). Since a voltage of +14 In the divider R550R565 (Fig. 2) is only possible when the unit is running normally horizontal, which voltage is +27 In the chip IC401 (pins 8, 13), the control system would be covered almost all the power components of the TV. So, no generation in the line scanning unit for any reason leads to disaster lock. Author unknown what the drafters meant by abbreviation NECK, but the phrase NECK OR NOTНING means "either sink or gone!" (the value of the NECK - the neck of the CRT).
Such an extraordinary and at the same time a simple construction of the protection device perfectly can be used in various Amateur radio developments, which required to calculate voltage dividers for their specific values the formula U2=U1R2/(R1+R2), where U1 is the supply voltage; U2 is the voltage in secondary the point of the divider; R1 - upper, R2 is the bottom resistor connected to the common wire. The voltage U2 is 0.5...3 more than the supply transistor Q581. In the above node approximate calculation of voltage U2 equal +5,38 (R594R595), +7,07 (R553R592), +7.5 V (R550R565).
The reverse side of this method of control - difficulties in diagnosis fault, because the failure of any of a very large number of members in the different nodes of the TV causes it to lock and the impossibility of anything to measure. To eliminate ambiguity in the diagnosis control system on the time repairs can be turned off, for example, between a closing the conclusions of the base and the emitter of the transistor Q581. However, before you do, it is necessary to ensure no short circuits in power circuits blocks of line (Q552, C526, D542, C543, C545, D543, etc.) and personnel (findings 8 and 13 of the chip IC401, etc.) scans and circuits connected to the stabilizers stress IC542 and IC543 (findings 1 and 2).
Will continue consideration of the characteristics of the microprocessor of the TV (see Fig. 1). The terminals 11 and 15 are inputs mode control with front panel (volume controls, switches programs). On pin 16 come the signals from output 2 infrared photodetector TFMSS380ESN VAS. Conclusion 30 - the reset input, the output 35 input control operation of the device limitations current rays tube voltage brightness (ABL) and contrast (ACL).
The microprocessor is synchronized built-in crystal oscillator with frequency 8 MHz (resonator H connected to the terminals 24 and 25).
The same as discussed above, the algorithm of functioning characteristic some other models of TVs company. For example, in the model JVC C-21ZE applied almost the same chipset main components, described in models, with the exception of the microprocessor (installed MM-С42SP in the housing 64 the conclusions). It is interesting that in so many models of firm release 1996-1998 applied completely different schematics and electronic components. I mean models that are comparable in price and functionality, for example, JVC-C-S2180M, etc.
Processing of the TV signal in the TV sets of JVC-AV-G21T, JVC C-21ZE in primarily provides many ofunctionality BIS М52343SP. The signal it receives directly to the drive image from the saw filter (findings 6 and 7). Block radio (inside ENCORE) has a video output (pin 52), which through PTSTS the switch on the chip LA7016 (IC251) takes place on the external video output or through cascades, in which Regency subcarrier audio - video input chip (pin 36). In addition, the unit radio channel a output (pin 3) control signal AGC system applied to the tuner.
From PTSTS at pin 52 is switched piezophilic emit the desired sound subcarriers, which comes to the input of the audio channel (pin 2). Depending on the model in the television set, three or four of the bandpass filter at the frequency of 4.5; 5,5; 6; 6,5 MHz in accordance with the standards M, B, G, I, D, K. Beep with output 46 BIS through the switch IC651 is supplied to the output amplifier CC - pin 2 IC AN5265 (IC601).
Most parts of the decoding device and the luminance channel are also included in BIS - bandpass and notch filters, the delay line in the luminance channel, the Recognizer of color television systems, amplifiers, devices as well as, shapers driving signals for the block scan, switches, signals R, G, B, etc. And all they are made on a single chip, without the use of external elements. Variables the parameters (frequency settings, time delays, etc.) set in digital form on bus BUS I/F (findings 11 and 15).
With findings 21-23 remove the color signals R, G, B for supplying the video amplifiers TV. Additional inputs R, G, B (pins 29, 27, 25) are used for power supply signals menu with microprocessor control.
In the signal processing system SECAM involves a number of nodes on chips MR (IC302) and U3660M-B (IC301). The latter is a delay line on the line (PLC), which operates when receiving a signal in the PAL system.
Consequently, the applied circuit design solutions allowed with no conversion a television signal in digital form to achieve multiple benefits fully digital TV at a low cost electronic components. Retail price for example, chips M52343SP at radio Rostov-on-don - about 15 $ MR - $ 5.
Common to most TVs nodes (power, scan, video amplifiers etc.) some significant features have not, although their share and we have the bulk of malfunctions of such devices. In this regard consider building a power supply TV JVC-AV-G21T. His feature - a wide interval of possible variation of the mains voltage - 90...270 V At short and 110...260 V for long-term work because in mainly the use of specialized chip, STR-S6707 SANKEN company. It widely used in many modern TVs different manufacturers. However, despite the relatively large supply permissible the mains voltage, the failure of these chips is a frequent phenomenon. In case difficulties with the replacement you can focus on it more powerful equivalents STR-S6708, STR-S6709 used in CRT televisions and 63 72 see From the point of view of reliability such replacement even preferred (replacement STR-S6708, STR-S6709 on STRS6707 invalid).
The failure of the power circuits switch-mode power supplies often accompanied by failures of other elements, and hence the power required to check the serviceability of the diode rectifiers, high voltage oxide capacitors, optocouplers, low ohmic resistors, as well as to ensure that no short circuits in the secondary circuit.
Diagnosis and repair of blocks of scans considered TVs any features has, and the relevant literature is now quite a lot.
In conclusion, look at how you can adjust some settings in the TV the service mode. Due to the significant volume of service instructions describe them completely is not possible, so we will focus only on major operations. Translated into Russian language instruction [3] sell at radio, however, the low quality of the translation can cause trouble with her use. The need for adjustment may occur when wrong the factory installed the operating parameters of the TV, after changing the some of the elements and nodes in the repair. So, in the instance that available the author was greatly exaggerated color saturation when working in the system SECAM. Finally, the largest volume adjusting operations required hold when replacing a faulty EPROM on a "clean", with no information.
Adjust the machine using the remote and menu on the TV screen. Service mode enter, by pressing both "DISPLAY" and "PICTURE MODE". On the screen showing the names of the three main blocks (stages) of the adjusting operations: 1. VSM PRESET 2. SUB VSM, 3. IF V/C ADJ. The blocks you want to select appropriate buttons (1, 2 or 3; mode 4 - SET UP MENU in the model no need to call).
The first group (block, segment) operations allows you to set the average values adjustments brightness (BRIGHT), contrast (CONT), saturation (COLOUR), the color tones NTSC (TINT) and definition (SHARP) in different modes of brightness image is BRIGHT (bright), STANDARD (middle) and SOFT (soft), consistently choose the button "PICTURE MODE".
The actual installation is performed by the "+" or "-" button group "PICTURE ADJUST", before anything, you must press the center button of this group in each of modes. Numeric values (they appear on the screen), recommended by the manufacturer for each of them (BRIGHT, STANDARD, SOFT), the following:
- TINT - 30, 30, 30;
- COLOUR - 15, 15, 15;
- BRIGHT - 15, 15, 15;
- CONT - 30, 24, 17;
- SHARP - 20, 15, 10
As seen on these values, modes BRIGHT, STANDARD, SOFT differ image contrast and to a lesser extent its clarity. Preset colour saturation is better to do on real images when taking different television programmes and work through the video input in PAL, SECAM, NTSC. If need to return to the previous menu (SERVICE MENU), press the MUTE button. Re-clicking the button displays the TV from the service mode.
The parameters of the second group (2. SUB VSM) is set similarly to the first, only instead of pressing the "PICTURE MODE" using the button "COLOUR SYSTEM". Modes and their the parameters are set the same buttons ("-", PICTURE ADJUST, "+"). The manufacturer's recommended values COLOUR-33, BRIGHT-17, CONT-30, SHARP-9 - for all systems when receiving broadcasting programs. While working through the video input can be necessary to adjust the parameters under the real sources include video input button TV/VIDEO).
The third group (3. IF V/C ADJ - FC, video, chroma) includes 14 parameters, the installation of which requires the filing of a calibrated test signals. It the detailed description is given in [3]. There are considered and ways to adjust the size vertically, the focus and the voltage at the anode of the picture tube and the implementation of the self-test.
Self-control system signals the malfunction by flashing the LEDs on and the display inscriptions NECK (sometimes OCP or X-RAY) if it's even possible. On breakdowns, breakages and short circuit in the unit scans the screen is not lit but LEDs continue to flash, of course, if the system itself is defective management, and the primary source is supplying it with a voltage of +5 V.
Literature
Author: J. Peter And Paul