Radio channel module on TDA8304 in 3USCT. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Телевидение

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The radio channel module (RCM) described here, the appearance of the printed circuit board of which is shown on the 1st p. cover of the magazine "Radio" No. 1 of this year, is intended to replace the MRK-2 module in 3USST TVs. It has relatively small dimensions, a small number of interconnects, lower current consumption and improved characteristics of horizontal and vertical synchronization systems. The use of an imported channel selector made it possible to exclude two blocks SK-M-24 and SK-D-24, to ensure the combination of antenna inputs MB and DM V, obtaining a high gain and reception of cable subbands. In addition, it became possible to use the MSN-501-9 voltage synthesizer module to control the TV. The disadvantages include the impossibility of working in the B / G standard (however, it is not used in Russia).

The horizontal synchronization system of the TDA8304 microcircuit used in the RTO eliminates interference on the screen with weak input signals and the presence of noise, as well as the appearance of dark bands at the edges of the image. In the frame scanning system of the microcircuit, the temperature stability of the parameters of the frame signal is improved, as a result, the best image interlacing is obtained. The parameters of the systems also depend much less on the supply voltage.

More details about the features of operation and functional units of the microcircuit are described in [1].

When developing RTOs, the schematic diagram of the TV set "Horizon-54CTV601" [1] was taken as a basis, in which the TDA4504B chip was used. Note that the TDA8304 chip differs from the TDA4504B only in improved characteristics.

Schematic diagram of RTOs is shown in fig. one.

(click to enlarge)

The received radio signal is amplified and converted to a 38,9 MHz IF signal by the A1.1 channel selector. From its IF output, the signal passes through a matching amplifier on a VT1 transistor to a SAW filter ZQ1. From its symmetrical output, the signal is fed to the radio channel processor (pins 9 and 10 of the DA1 chip). In the microcircuit, it is amplified and detected. From its output 20, the video signal (from the 6,5 MHz audio IF) arrives at the notch filter ZQ2, where the audio IF signal is suppressed. As a result, based on the VT4 transistor and pin 16 of the microcircuit, there is a full color television video signal (PCTV).

From the output of the emitter follower on the transistor VT4, the video signal is fed to connector X5, to which the video input of the VCR is connected. At the same time, the video signal comes to the internal switch (via pin 16) of the DA1 chip. The "AV / TV" modes of the TV are controlled by a key on the VT6 transistor: low voltage (O V) at the emitter of the transistor turns on the internal signal (TV), high (5 V) - external signal (AV). The control voltage acts on pin 18 of the DA1 chip and pin 11 of the DA3 chip (the latter is used to control the sound switch).

The external video signal is fed to the X4 connector, and the output and input audio signals are sent to the X6 connector, to which the VCR is connected.

The video signal after switching through pin 15 of the DA1 chip and the R31C29 circuit passes through connector X2 to the color module (MC-31-1). XZ connector - reserve.

From pin 20 of the DA1 chip, the video signal containing the audio IF, through the C49R61 circuit, comes to the ZQ3 band-pass filter, which selects the 6,5 MHz audio IF signal coming through pin 3 of the DA3 chip to the audio demodulator. Further sound processing takes place in this chip.

From the output of the regulated amplifier through pin 17 of the DA3 microcircuit, the R74R75C64 circuit and the X7 connector, the 3H signal passes to the power amplifier in the BU-3-1 block. Volume control is provided by changing the constant voltage at pin 16 of the DA3 chip. It comes to pin 3 of the X11 connector from the MSN-501-9 block. The initial voltage is set by the divider R69R70.

We will not describe the operation of all elements and circuits of each output of the microcircuit and its nodes. Let us consider here only the features of connecting the vertical and horizontal scanning synchronization outputs, as well as the OOS circuits and the strobing signal (SSC).

Linear trigger pulses with an amplitude equal to 0,8 ... 1 V are formed at pin 29 of the DA1 microcircuit. After passing through the emitter follower on the VT3 transistor, they enter through pin 3 of the X9 connector to the MS-1 line scan module. The circuit is connected in the same way as in [2].

For the reasons discussed in [2] (different shape and amplitude), the control pulses for the vertical scanning output stage are fed through an inverter amplifier on a VT2 transistor. From its collector, frame pulses with an amplitude of 10 ... 11 V come through contact 7 of the X10 connector to the frame scan module MK-1-1.

As for the environmental protection, it is applied without the protective properties described in [2]. The R27R28 divider in the MRK is installed to restore the constant component in the OOS circuit and unlock the sweep nodes inside the DA1 chip. Capacitor C26 serves to pass the sawtooth component and prevent shunting of the divider by the vertical scan module circuits. The trimming resistor R76 regulates the level of the vertical sawtooth signal, and hence the frame rate. Resistor R14 in the MK-1-1 module no longer performs this function.

SSC strobing pulses through pin 30 of the DA1 processor and pin 4 of the connector come to the color module. The R47R49 divider reduces the level of the 60 V flyback horizontal pulses to 5 V to form SSC superstrobe pulses. The R47R48 divider serves to obtain the necessary constant component of these pulses.

As for the beam current limiting circuit (OTL), in 3USCT TVs, with an increase in the kinescope current, the voltage in the circuit increases, and in the CTV-601 TV, on the contrary, it decreases. However, 3USCT TVs have a circuit in which the voltage also decreases in proportion to the kinescope current. This is the Stabilization Signal circuit. To it and you need to connect the wire EXC.

Trimmer resistors SPZ-38 are used in RTOs. The remaining resistors are any (suitable in size). Capacitor C38 - K71 -7 with a tolerance of 1% for a voltage of 250 V (necessarily highly stable), C7 - K73-17 for a voltage of at least 63 V. The rest are small-sized imported ones. Throttles - DPM, DMV.

Coils L3-L5, L8, filter ZQ1 are taken from the submodule SMRK-1-5. Filters ZQ2, ZQ3 - FP1R8-63,02, FP1P8-62,02, respectively, are also available in SMRK-1-5, but imported ones are also suitable.

We will replace the KT368AM (VT1) transistor with KT368BM, KT399AM, KT645B (VT2) - with KT645A, KT3102BM (VT3-VT5) - with KT3102 with any other letter, KT3107BM (VT6) - with KT209 also with any letter index. Instead of the TDA8304 chip, you can install TDA4504B, KR1087XA6, instead of TDA3827 - KR1087XA5, and instead of the stabilizer (+5 V) 78L05 - KR1157EN502A, but KR142EN5A is also suitable.

The article in [4] will help to find out the characteristics and choose the desired channel selector.

When installing a new RTO, some changes should be made to the blocks MTs-31-1, BU-3-1, PS and MSN-501-9 of the TV.

It would be more expedient to install the MSN-501 module on the TV, but the author did not have it, therefore, the alteration of the MSN-501-9 module is described below. Those who wish can connect to RTOs both MSN-501 and regular, USU-1-15. In the latter case, it is necessary to add a resistor R5, shown by a dashed line, and correct the desoldering of the corresponding connectors. Elements R59, R60, VT5, C48, also shown by a dashed line, are installed if there is no access to the tuning resistor R22 in the MCH block. The adjustment "About APCG" is done in the MRK block by placing the indicated elements and removing the resistor R57.

The wiring diagram of the connecting harnesses going to the RTO module from the TV units, as well as from the RTO to the PS connection board, is shown in fig. 2.

On the PS board, pins are inserted into the free holes for pins 5 and 6 of connector X5 and, having soldered insulated wires to them, connect them to pin 10 of connector X4 and pin 2 of connector X1 of the board, respectively.

Just as in [5], all connecting harnesses coming from the MSN-501-9 module are soldered, extended and soldered according to the diagram in Fig. 2. In the MSN-501-9 block itself [6], the elements R75, R76, R83-R85, VD1, VD14, VD15, VD17, VT17, VT18, VT20 are removed, the VD4 diode is replaced with a jumper, and the resistors R43 (56 kOhm) and R42 (47 kOhm) is replaced with new ones with ratings of 510 and 620 kOhm, respectively.

In the MC-31-1 color module [3], remove the elements VD1, R32, and install a jumper instead of the resistor R31. When using blocks MSN-501 and MSN-501-9, resistors R4-R6 in the color module are replaced with jumpers. In block BU-3-1 [3], the elements R23, R22, VD1, C10 are removed (in the case of USU-1-15, they must be left).

After assembling the module and checking for short circuits and installation errors, it is inserted instead of MRK-2 and all connectors are connected according to the diagram in fig. 2. Before turning on the TV, you need to set the sliders of all tuned resistors to the middle position. The same applies to the tuned resistor R22 in the MSN-501-9 block. The trimmers of the coils L5, L8 are screwed into the MRK so that in the coil L5 the trimmer protrudes relative to the cut of the frame by approximately 3 ... 4 mm, and in the coil L8 - by 1 ... 2 mm.

After turning on the TV, a raster should appear. In its absence, voltages of 12 and 135 (130) V are checked at the outputs of the power module. In the case of normal values, the voltage (about 3,3 V) is measured at pin 5 of the DA1 MRK chip. If it is not there, check the elements R27, R28, C26, as well as the presence of a voltage of 12 V on pin 4 of connector X5 of the PS board.

When the raster glows, the frequency of lines and frames is preliminarily set by trimming resistors R46 and R76, respectively. In the power supply module MP-1 (MP-3-3), output voltages of 135 (130) and 12 V are set with trimmer resistors.

If you have an RF generator and an oscilloscope, carry out the adjustment as indicated in [1, p. 308]. It should only be borne in mind that the reference designations of the adjusting elements in the MRK are different and they will have to be compared with similar functions in the CTV-601 TV (see above).

In the absence of a generator and an oscilloscope, the adjustment is carried out using an avometer (multimeter). The adjustment begins with setting the frequency and phase of the line scan pulses. To do this, the pins of the XN2 plug in the RTO are closed to each other and, by rotating the engine of the tuning resistor R46, they ensure that there are no inclined horizontal lines on the screen and the image slowly moves horizontally. After that, the pins of the XN2 plug are opened.

To adjust the phase of the control pulses with a trimmer resistor R13 in the raster correction submodule (SKR-1, SKR-2), the image size is reduced horizontally and the engine of the trimmer resistor R35 is installed in the MRK so that there are no inversions and image compression from the left and right edges of the raster ( symmetry of the sides of the image). Then, by rotating the slider of the tuning resistor R16, the AGC voltage is set at pin 4 of the channel selector A1.1 so that there is no noise, distortion of vertical lines and darkening in the upper part of the raster (negative) in the image when receiving signals on all subbands.

Next, the APCG system is turned off (blocked), for which the pins of the plug XN1 of the module are closed. Using the SB8, SB9 buttons in the MCH, they are tuned to a channel and enter the setting into the memory of the MCH processor. The voltage at pin 21 of the DA1 microcircuit in the MRK is constantly measured, which should be in the range of 5,5 ... .6,5 W.

Having remembered the voltage value at pin 21 of the DA1 microcircuit in the RTO, the blocking of the APCG system is removed (the pins of the XN1 plug are opened). In this case, the voltage at pin 21 will either increase to 10 ... 11 V, or decrease to 4 V, and the tuning to the station will "leave". The coil trimmer L5 achieves the same voltage value at pin 21 of the microcircuit, which was before the APCG system was turned on. Tuning to the station should be restored. Turning the APCG system on and off (by closing and opening the pins of the XN1 plug), check the correct installation of the APCG: the setting should not be changed. Otherwise, the adjustment will have to be repeated.

After that, with the automatic search button for working channels in the MCH, you should tune in to them. In this case, there should be a “capture” of the channel and its “holding”, as well as the absence of “jumping” of stations.

Starting to tune the IF sound channel (6,5 MHz), tune in to a working station and, by rotating the trimmer of the L8 coil in the RTO, achieve the highest sound volume with the least noise.

Next, check the operation of the AV / TV switches. By pressing the "AV" button on the remote control, they make sure that there is a picture and sound from the VCR, having previously sent signals from it to the connectors X4-X6 of the module. When you press the "TV" button, the reception of on-air programs returns.

Trimmer resistor R66 set the level of the audio output signal to the VCR.

It is advisable to install the channel selector (tuner) with a FONO type antenna input, which allows using an adapter cable between the tuner and the TV's antenna input jack. Tuners with an SNIR input socket for direct connection of the antenna cable to the tuner are inconvenient, since you will have to connect the cable from the bottom of the rear wall of the TV, for which you will need to cut a window in it.

The jack for connecting a VCR ONTS-VG-5/16-R can be installed instead of the vacant UHF antenna jack. True, for this you will have to expand the hole.

The UPCHZ-2 microassembly in a typical inclusion can also serve as a sound demodulator. This will simplify the assembly a little, eliminate the process of tuning to the sound IF, and the need for an L8 coil will disappear.

Literature

1. Elyashkevich S. A., Peskin A. E. TV sets of the fifth and sixth generations "RUBIN", "HORIZON", "ELECTRON". Device, adjustment, repair. - M.: Solon-R, 2000.
2. Brylov V. Chip TDA8362 in 3USCT and other TVs. - Radio, 1998, No. 10, p. 13-16.
3. Elyashkevich S. A., Peskin A. E. TV sets 3USCT, 4USCT, 5USCT Device, adjustment, repair. - M.: MP "Symbol-R", 1993.
4. Burkovsky A. Modern television channel selectors. - Radio, 1999, No. 6, p. 6, 7; No. 7, p. 8, 9.
5. Brylov V. 68 programs on TVs 3USCT-Radio, 1997, No. 11, p. 8-10; No. 12, p. 8-10.
6. Album of schemes for portable and stationary TVs III, IV, V, VI generations of black and white and color images.

Author: A.Natnenkov

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