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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING TVs with digital processing and control. Methods of adjustment, repair. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение The control system for the operation of blocks and nodes in digitally controlled TVs provides reliable protection of devices in case of failure. If a malfunction occurs, especially in power circuits (line and vertical scanners, secondary voltage stabilizers, etc.), it puts the TV into standby mode, and it is impossible to turn it on. How to turn off the protection system for repairs in this case is described in the published article. The author examines the operation of such TVs using the JVC-AV-G21T as an example, and also gives recommendations on entering the service mode and how to adjust. A significant reduction in prices for household appliances (in US dollars) in recent years has also affected many TV models. To the greatest extent, this applies to the most popular devices on kinescopes with a screen diagonal of 37, 51 and 54 cm. Already in 1992, many manufacturing firms managed to bring retail prices for televisions with a kinescope with a screen size of 54 cm diagonal to 300. ..350 dollars, without reducing their technical level and quality. One can only guess what their true cost is, but some ways to significantly reduce production costs can be clearly seen. As an example, consider a fairly popular TV JVC-AV-G21T (acquired by the author in 1996). It continued to be produced in a slightly modernized form in 1998 (model JVC-AV-2130EE at a price of $345, see [1]). Let's briefly dwell on the technical characteristics of the TV. The received frequency intervals 46,25 ... 168,25, 175,25 ... 463,25, 471,25 ... 863,25 MHz are covered by the CEEU534-803 tuner, a tunable voltage synthesizer, i.e. reception is provided in all broadcast and cable channels (1-12, 21-60, S1-S41). Working radio standards - B, G, D, K, K1, I, color systems - PAL / SECAM, and from video inputs - NTSC3,58 / NTSC-4,43, which are selected both automatically and manually. In addition, the device is equipped with video and audio inputs on the front and rear panels and C3adi video and audio inputs (RCA connectors). Adjustment and control is possible from the front panel and from the remote control, provides quick adjustments for brightness, contrast, color saturation or tone (in the NTSC system), clarity and volume. Power consumption - 70 W (maximum - 105 W) at mains voltage 90...260 V. The listed parameters in no way allow classifying this model as "simple", and, according to the author, JVC managed to ensure low cost mainly by eliminating most of the technological adjustment operations on the assembly line. Previously (20 years ago) each workplace of the traffic controller was equipped with expensive measuring equipment and accessories. In addition, highly qualified personnel were required for most of the technological adjustment and testing operations. The JVC-AV-G21T TV (and many other models of the company in recent years) according to the domestic classification belongs to the fifth generation, i.e. to analog-to-digital TVs with microprocessor control and analog processing of audio and video signals [2]. However, some features of the sixth generation devices are also inherent in it: most technological adjustment operations are performed digitally by programming a non-volatile electrically reprogrammable memory device EEPROM (EEPROM). In our case, this is the AT24C04 chip (IC702). Since this adjustment method practically does not require the connection of measuring equipment to test points inside the TV and the adjustment of various elements with variable parameters (inductors, trimmers and capacitors), it is possible to significantly reduce production costs. In addition, by adjusting several instances of TVs, in the future, you can enter the primary information into the EEPROM by the programmer. In this case, it will only be necessary to check the devices coming off the assembly line, and if any parameter deviates from the nominal value, only its adjustment from the control panel will be necessary. A simplified block diagram of the JVC-AV-G21T TV is shown in fig. 1. It includes a switching power supply on a SANKEN STR-S6707 (IC901) chip, a line scanner on discrete elements, a vertical scanner on a SANYO LA7837 (IC401) chip, an all-wave tuner CEEU534 (TU001), a multifunctional television signal processing unit based on chips M52343SP (IC201), M52325P (IC302) from MITSUBISHI, U3660M-B (IC301), audio and video input switches based on chips LA7016 (IC251, IC651) from SANYO, audio frequency amplifier based on chip AN5265 (IC601) from MATSUSHITA, system control and settings on the M37212M4-050SP microprocessor (IC701) and a number of voltage stabilizers and nodes on discrete elements.
In terms of the volume of tasks to be solved, first of all, one-chip microcomputer M37212M4050SP (IC701) from MITSUBISHI should be singled out. JVC traditionally widely uses microprocessors and other microprocessors of this company in its video equipment, which are distinguished by very high reliability. Spontaneous, without noticeable external causes, failures of its microprocessors are very rare, which cannot be said about the products of some other companies. For example, FUNAI TV microprocessors TMP47C434N - R214 (QSMQAOZTS015) and TMP47C634AN - R584 (QSMQAOZTS045), notorious among repairers, provided considerable profit to our companies trading in electronic components. Unfortunately, during the operation of TVs, spontaneous failure of these LSIs is widespread. The microprocessor is powered (+5 V) by a specialized stabilizer IC703 based on the L78LR05E-MA chip. It also contains a reset device for resetting the microprocessor when the device is turned on. The VDD power circuit (pin 27) of the microprocessor is carefully decoupled from interference by a U-shaped filter С709L701C711. The IC701 microprocessor provides most of the functions for the operational control of all other functional blocks of the TV and control over the execution of commands. In addition, he is entrusted with the task of technological adjustments at the production stage, for which the TV set is built with virtually no tuning elements (coils, resistors and capacitors). Of the traditional manual adjustments, there are focusing and voltage trimmers on the anode of the A51LEC098X kinescope in the horizontal scanner and a vertical image size control in the vertical scanner. On a digital bidirectional line (presumably I2C, the designation on the diagram is BUS I / F), the microprocessor exchanges information with the multifunctional LSI for processing a television signal IC201 (signals SCL1 and SDA1 - at pins 37 and 39 of the microprocessor) and with a non-volatile memory device IC702 (signals SCL2 and SCDA2 - on pins 36 and 38). All these signals are output to the CN00C control connector, which allows programming the memory device from an external computer, connecting a logic analyzer or other measuring instruments for diagnostics and repair in production conditions and service centers. The purpose of the remaining control outputs (outputs) of the microprocessor is as follows: 4 - signal for switching the vertical scan mode 50/60 Hz (supplied to pin 5 of the IC401 chip); 8 - a signal that turns on the LED indicating the OFF TIMER mode on the front panel; 9 - control signal for the volume control in the IC601 chip; 10 - sound blocking signal by shorting to a common wire output 4 of the IC601 chip (through a matching stage); 19 - turning on the operating mode of the TV by applying a voltage of +5 V to the transistor Q942 of the power supply (in standby mode, the transistor is closed); 20-22 - tuner voltage synthesizer control signals - CLOCK, DATA, ENABLE (synchronization, data, tuning resolution); 31 - signal to turn on the CF124 notch filter at 4,5 MHz in the video path when working with signals of the M and N standards (the filter only works when docked through the video input with some NTSC TV tuners; when connecting VHS VCRs or video disc players, the presence or absence of a filter is indifferent; docking through the antenna input with NTSC equipment is not provided in the model); 31, 32 - signals for controlling the modes of the audio path, which ensure its switching to receive television signals with a frequency separation of 5; 6 and 6,5 MHz (the desired mode can also be selected manually from the remote control); 41 - control signal for the switch of audio and video inputs on IC251, IC651 microcircuits; 50-52 - signals B, G, R of the setup and adjustment menu driver are fed to the corresponding inputs of the IC201 chip (pins 25, 27, 29) of the television signal processing channel. To ensure the control of the operability of the TV nodes and the correct functioning of the microprocessor has the following inputs (outputs): 1 and 2 - for supplying horizontal pulses from the TDKS winding and personnel pulses from the output stage of the IC401 microcircuit (through buffer stages and resistive attenuators), as well as 7 - to control the state of the protection system of the units of the reamer. Since the construction of a protection device has specific features, it is advisable to consider its operation in more detail using a circuit fragment in Fig. 2. The key on the Q581 transistor provides tracking of the presence of three voltages at once. In the initial state, with a properly working TV, it is securely closed. Since there is no voltage on its collector, level 0 is fed through the NECK circuit to pin 7 of the microprocessor. Controlled power circuits through voltage dividers, diodes and a common resistor R549 are connected to the base of the transistor Q581: for a voltage of +8 V, these are R594, R595, D568, and for +12 V - R592, R593, D567. The +27 V voltage is indirectly controlled, since the R550R565 divider is connected through the D565 diode and vertical deflection coils to the midpoint of the vertical scan output stage in the IC401 chip (pin 12) with a voltage of +14 V.
In the normal state, all diodes are closed by voltages applied to the cathodes from the corresponding dividers. With the disappearance of any of these voltages, one of the diodes opens and, therefore, the transistor Q581 through the corresponding resistor in the lower arm of the divider (connected to the common wire). A voltage of +5 V appears on the transistor collector and the NECK conductor, which means an emergency mode for the processor. As a result, at pin 19 and the P-ON / OFF conductor of the microprocessor (see Fig. 1), the voltage drops to zero, the transistors Q941, Q942 in the power supply close, the +12 V voltage (HD-VCC) that feeds the scanner disappears, and the TV goes into standby mode. Since the presence of a voltage of +14 V on the R550R565 divider (Fig. 2) is possible only with a normally operating line scanner, from which +27 V is applied to the IC401 chip (pins 8, 13), almost all power elements of the TV are covered by the control system. So, the lack of generation in the line scanner for any reason leads to emergency blocking. The author does not know what exactly the developers meant by the abbreviation NECK, but the phrase NECK OR NOTHING means "either pan or go!" (there is a value NECK - the neck of the kinescope). Such an extraordinary and at the same time simple construction of a protection device can be used in various amateur radio developments, which requires calculating voltage dividers for their specific values according to the formula U2 = U1R2 / (R1 + R2), where U1 is the supply voltage; U2 - voltage at the middle point of the divider; R1 - top, R2 - bottom resistor connected to a common wire. The voltage U2 must be 0,5 ... 3 V more than the supply transistor Q581. In the node discussed above, the approximate calculated voltages U2 are +5,38 V (R594R595), +7,07 V (R553R592), +7,5 V (R550R565). The reverse side of this method of control is great difficulty in diagnosing faults, since the failure of any of a very large number of elements in the most diverse nodes of the TV leads to its blocking and the inability to measure anything. To eliminate ambiguity during diagnostics, the monitoring system can be turned off for the duration of repair work, for example, by shorting the base and emitter terminals of the Q581 transistor together. However, before doing this, it is necessary to make sure that there are no short circuits in the power circuits of the line blocks (Q552, C526, D542, C543, C545, D543, etc.) and personnel (pins 8 and 13 of the IC401 chip, etc.) scans and circuits connected to voltage regulators IC542 and IC543 (pins 1 and 2). Let's continue consideration of features of functioning of the TV microprocessor (see fig. 1). Pins 11 and 15 serve as mode control inputs from the front panel (volume controls, program switches). Pin 16 receives signals from pin 2 of the infrared photodetector TFMSS380ESN of the remote control system. Pin 30 - reset input, pin 35 - input for monitoring the health of the device for limiting the current of the kinescope beams along the brightness (ABL) and contrast (ACL) circuits. The operation of the microprocessor is synchronized by a built-in crystal oscillator with a frequency of 8 MHz (X701 resonator is connected to pins 24 and 25). The same as discussed above, the functioning algorithm is also characteristic of some other models of the company's TVs. For example, the JVC-C-21ZE model uses almost the same chipset of the main components as in the described model, with the exception of the microprocessor (M37102M8-C42SP is installed in a 64-pin package). It is interesting that in very many models of the company produced in 1996-1998. completely different circuit solutions and element base are used. This refers to models that are comparable in price and functionality, for example, JVC-C-S2180M, etc. TV signal processing in JVC-AV-G21T, JVC-C-21ZE TVs is mainly provided by the M52343SP multifunctional LSI. The signal to it goes directly to the image IF from the SAW filter (pins 6 and 7). The radio channel block (inside the LSI) has a video output (pin 52), from which the PCTS passes through a switch on the LA7016 chip (IC251) to an external video output or through cascades in which audio subcarriers are notched - to the video input of the microcircuit (pin 36). In addition, the radio channel block has an output (pin 3) of the control signal of the AGC system applied to the tuner. From the PCTS at pin 52, the switched piezo filters select the desired audio subcarrier, which comes to the input of the sound channel (pin 2). Depending on the model, three or four band-pass filters are installed on the TV at frequencies of 4,5; 5,5; 6; 6,5 MHz in accordance with the standards M, B, G, I, D, K. The audio signal from pin 46 of the LSI through the IC651 switch goes to the output amplifier of the AF - pin 2 of the AN5265 (IC601) chip. Most of the nodes of the decoding device and the luminance channel are also included in the LSI - bandpass and notch filters, a delay line in the luminance channel, a color television system recognizer, amplifiers, matrixing devices, driver signal generators for the scanner, R, G, B signal switches, etc. And all of them are made on a single chip, without the use of external elements. Variable parameters (tuning frequencies, delay time, etc.) are set digitally via the BUS I / F bus (pins 11 and 15). From pins 21-23, color signals R, G, B are removed for feeding to TV video amplifiers. Additional inputs R, G, B (pins 29, 27, 25) are used to supply menu signals from the control microprocessor. A number of nodes on the M52325P (IC302) and U3660M-B (IC301) microcircuits take part in the signal processing of the SECAM system. The latter is a Line Delay Line (PCD) that also works when receiving a signal in the PAL system. Consequently, the applied circuit solutions made it possible to achieve many advantages of fully digital TVs at a low cost of the element base without converting the television signal into digital form. The retail price, for example, of M52343SP chips on the radio market of Rostov-on-Don is about $15, M52325P is $5. The nodes common to most TVs (power supplies, sweeps, video amplifiers, etc.) do not have any significant features, although they account for the bulk of the malfunctions of such devices. In this regard, consider the construction of the power supply of the JVC-AV-G21T TV. Its peculiarity is a wide range of permissible changes in mains voltage - 90...270 V for short-term and 110...260 V for long-term operation, which is mainly due to the use of a specialized SANKEN STR-S6707 chip. It is widely used in many modern TV models by various manufacturers. However, despite the rather large margin for the allowable network voltage, the failure of these microcircuits is not uncommon. In case of difficulty with replacement, you can focus on its more powerful functional equivalents STR-S6708, STR-S6709, used in TVs with 63 and 72 cm kinescopes. From the point of view of reliability, such a replacement is even preferable (replacing STR-S6708, STR-S6709 with STRS6707 not allowed). The failure of power microcircuits of switching power supplies is often accompanied by failures of other elements, therefore, before switching on, it is necessary to check the serviceability of diode rectifiers, high-voltage oxide capacitors, optocouplers, low-resistance resistors, and also make sure that there are no short circuits in the secondary power circuits. Diagnostics and repair of scanners of the TVs in question do not have any features, and there is quite a lot of relevant literature now. In conclusion, let's look at ways to adjust some of the TV's parameters in service mode. Due to the significant volume of the service manual, it is not possible to describe them in full, so we will focus only on the main operations. The instruction [3] translated into Russian is sold on radio markets, but the low quality of the translation can cause difficulties in its use. The need for adjustment may arise if the operating parameters of the TV set are incorrectly set at the factory, as well as after replacing any elements and assemblies during repair. So, in the copy available to the author, the color saturation was significantly overestimated when working in the SECAM system. And finally, the largest amount of adjustment operations is required to be carried out when replacing a faulty PROM with a "clean" one, without information. Adjust the unit using the remote control and the menu on the TV screen. The service mode is entered by simultaneously pressing the "DISPLAY" and "PICTURE MODE" buttons. At the same time, the names of three main blocks (stages) of adjustment operations are displayed on the screen: 1. VSM PRESET, 2. SUB VSM, 3. IF V/C ADJ. The necessary blocks are selected by the corresponding buttons (1, 2 or 3; mode 4 - SET UP MENU does not need to be called in this model). The first group (block, stage) of operations allows you to set the average values of brightness (BRIGHT), contrast (CONT), saturation (COLOUR), NTSC hue (TINT) and sharpness (SHARP) in various image brightness modes - BRIGHT (bright), STANDARD (medium) and SOFT (soft), sequentially selected by the "PICTURE MODE" button. The setting itself is carried out using the "+" or "-" buttons from the "PICTURE ADJUST" button group, before which it is necessary to press the central button from this group in each of the modes. The numerical values (they are displayed on the screen) recommended by the manufacturer for each of them (BRIGHT, STANDARD, SOFT) are as follows:
As can be seen from these values, the BRIGHT, STANDARD, SOFT modes differ in image contrast and, to a lesser extent, in its clarity. Presetting color saturation is best done using real images when receiving various television programs and working through a video input in PAL, SECAM, NTSC systems. If you want to return to the previous menu (SERVICE MENU), press the "MUTE" button. Pressing it again takes the TV out of service mode. The parameters of the second group (2. SUB VSM) are set similarly to the first, but instead of the "PICTURE MODE" button, the "COLOR SYSTEM" button is used. The modes and their parameters are set with the same buttons ("-", PICTURE ADJUST, "+"). COLOUR-33, BRIGHT-17, CONT-30, SHARP-9 values recommended by the manufacturer - for all systems when receiving on-air programs. When working through the video input, it may be necessary to adjust the parameters for real signal sources (turn on the video input with the TV / VIDEO button). The third group (3. IF V / C ADJ - IF, video, color) includes 14 parameters, the installation of which requires the supply of calibrated test signals. Its detailed description is given in [3]. There are also considered ways to adjust the vertical size, focusing and voltage at the anode of the kinescope, as well as the implementation of the self-control function. The self-monitoring system signals faults by flashing LEDs and displaying NECK (sometimes OCP or X-RAY) on the screen, if this is still possible. In case of breakdowns, breaks and short circuits in the scanner, the screen does not light up, but the LEDs continue to blink, of course, if the control system itself is working, and the primary power source supplies +5 V to it. Literature
Author: Yu.Petropavlovsky
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