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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Replacing the K416KN1 chip and the BPI-411 power supply in TVs. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Телевидение When repairing TVs, radio mechanics and radio amateurs often face the problems of replacing elements (not available for sale) and blocks (in order to increase the reliability of the devices). The author of the selection of materials published here shares his experience of overcoming these difficulties by using the equivalent of the K416KH1 chip and replacing the BPI-411 power supply with a more reliable MP-3-3. Analog chip K416KN1 When repairing radio equipment, we repeatedly had to deal with the failure of the K416KN1 chip used in the pseudo-sensor television program selection unit (BVTP) of Elektronika-Ts431 and Elektronika-Ts432 TVs, which are quite widespread. It is almost impossible to buy it, since it is no longer produced. To restore the performance of such TVs, it was necessary to develop a replacement option for this microcircuit, which is offered to repairmen and radio amateurs. The K416KN1 microcircuit is a switch with two sets of electronic keys controlled by triggers. When you press the BVTP button of one of the programs, the trigger corresponding to the button operates, which controls two keys. One of them supplies +27 V voltage to the tuning resistor of the selected program, and the second, opening, turns on the desired tuning sub-range selection node and the indicator of this program. When developing an analogue-equivalent of a microcircuit, the task was to obtain a relatively simple device with minimal changes in the TV. The assembled equivalent of the microcircuit was tested in TVs and proved to be excellent. No differences or failures in the operation of devices with such a replacement were observed. The schematic diagram of the analogue is shown in fig. 1. Its main feature is the use of comparators on the op-amp instead of keys that switch the voltage of +27 V. The fact is that most of the available microcircuits, which include switches on field-effect or bipolar transistors, are not capable of switching such a voltage, and the use of individual transistors would lead to a significant increase in the size of the equivalent. The use of comparators required only two microcircuits DA1, DA2 and two resistors.
The comparators are controlled by flip-flops on microcircuits DD1, DD2, on which a dependent quasi-sensor switch is assembled. With a short-term supply (through a button) to any of the inputs of the +12 V voltage switch, a high level is set at its corresponding output, and a low level is set at all other outputs. These levels are fed to the non-inverting inputs of the comparators, and the voltage in the range of +2...4 V is applied to the inverting inputs from the divider R9R10. As a result, at a low level at the inputs of the comparators, a voltage close to zero is set at their outputs, and at a high level at the input, a voltage of +26,5 V appears at the corresponding output, which is necessary to set up the TV. Elements of the DD3 chip control the subrange selection circuits and LED indicators, inverting the signals coming from the switch outputs. Capacitor C1 ensures that the first switch trigger is set to a single state when the TV is turned on, i.e., turning on the first program (which is configured on button 1). Unlike the K416KN1 microcircuit, it is necessary to separately supply the +12 V supply voltage available in the BVTP to the analogue. In addition, the program switch buttons on the TV are connected with one contact to the terminals (ISIS, 22-24) of the K416KN1 chip, and their second contacts are connected together with a common wire. The latter must be disconnected from the common wire by cutting one printed conductor on the BVTP board and applying +12 V voltage to them through the jumper. This is due to the fact that the equivalent triggers are controlled by a positive voltage, and the microcircuit triggers are connected by connecting their inputs to a common wire. This is the difference between connecting an equivalent from a microcircuit. It is also necessary to solder the output of the diode connected to the output of the 24 microcircuit on the BVTP board. The printed circuit board of the device is made of double-sided foil fiberglass and is shown in fig. 2. Its small size makes it possible to place an equivalent inside the BVTP in place of a soldered faulty microcircuit.
The board (Fig. 2, b) has resistors and a surface-mount capacitor of size 1206 on the side opposite to the placement of other parts (Fig. 2, a). On the same side, the places on the printed conductors are indicated, to which the wires are soldered, which serve as analog outputs. They should be marked. The use of plenary elements made it possible to reduce the dimensions of the board. The LM324 (DA1) chip can be replaced with K1401UD1, K1401UD2, and LM358 (DA2) - with CA3240, KR1040UD1. Microcircuits of the K561 series are interchangeable with similar ones from the KR1561 series. Instead of diodes of the KD510 series, you can use diodes from the KD521, KD522 or similar series. All diodes are soldered perpendicular to the board surface also in order to reduce its size. The assembled analog is soldered with wires-outputs to the BVTP of the TV instead of the remote microcircuit in accordance with its circuit. A correctly assembled and connected equivalent does not need to be adjusted. In the case of fuzzy switching programs when you press the buttons, you can pick up the resistor R8. However, at the nominal value indicated on the diagram, the assembled copies of the device worked reliably. Replacement of BPI-411 with MP-3-3 When repairing domestic TVs, radio amateurs often encounter failures in the BPI-411 power supplies in TVs, especially the Orizon type, for example Orizon-51TTs449D. One of the very common malfunctions can be called the repeated operation of the protection in the unit. At the same time, it is operational, but when you turn on the TV, it often starts up with only a few attempts. All elements in the block are in good order, the replacement of oxide capacitors also does nothing. Slightly improves the operation of the source by increasing the capacitance (up to 200 μF) of the capacitor C3, connected between the terminals of the collector and emitter of the transistor VT2. However, it does not completely eliminate the problem. To get rid of such problems, it is best to replace the BPI-411 with a more reliable and stable power supply MP-3-3 (or similar) used in third-generation TVs. It has all the voltages necessary for the operation of these TVs, except for the 6,3 V voltage that supplies the kinescope filament, since in third-generation TVs the voltage for the kinescope filament is removed from the horizontal scan transformer. For replacement, it is required, first of all, to make a simple adapter, the diagram of which is shown in Fig. 3 because the connectors on these power supplies don't match. The kinescope filament voltage is applied to pins 4 and 5 of the X4 connector of the adapter. Voltage can be obtained in different ways. It is best to add a separate transformer to the TV with a voltage on the secondary winding of 6,3 V. It should provide a current in the range of 0,6 ... 0,8 A. There is plenty of space to place the transformer on the TV.
The second way is to connect the kinescope filament through a resistor with a resistance of 2-3 ohms and a power of at least 4 W to the winding of a 7-8 line transformer, as is done in third-generation TVs. The winding in the horizontal transformer of these TVs is not involved. Finally, the third way is illustrated in Fig. 3. It consists in adding one more winding to the TPI-4-2 transformer in the MP-3-3 power source. To do this, solder the screen that closes the transformer, and wind six to seven turns of wire with a diameter of 0,5 ... 0,7 mm over the existing windings. It is very convenient to use a mounting wire for this purpose, for example, MGTF. To check the voltage on the additional winding, turn on the MP-3-3 power source to the network, preloading the +130 V circuit with an incandescent lamp (220 V, 100 W) and soldering a PEV-7 resistor with a resistance of 10-15 Ohm to the additional winding. Instead of a resistor, you can also use an incandescent lamp for a voltage of 6,3 V and a power of 4 ... 5 W. Measure the voltage across the resistor (or lamp) with a multimeter in AC voltage measurement mode. If necessary, if the voltage value does not correspond to 6,3 V, add or reduce the number of turns in the winding. Exactly this voltage can be achieved by selecting an additional resistor R1d. Having received the required voltage, the transformer shield is installed in place. The MP-3-3 power supply board for replacement must be selected with small-sized line filter capacitors. If K50-31 capacitors screwed with nuts are installed on it, they must be replaced with K50-35 or imported ones. You can use one capacitor with a capacity of 150-200 microfarads for a voltage of at least 350 V. The new board is freely placed in place of the old one. The power supply installed in this way in the specified TV has been working reliably for several years. It should also be noted that the cost of the MP-3-3 power supply is almost two times lower than the cost of the BPI-411. Author: I.Korotkov, Bucha village, Kyiv region, Ukraine
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