DIY samsung music center repair

In detail: do-it-yourself repair of samsung music centers from a real master for the site my.housecope.com.

One of the most common malfunctions of music centers is the failure of the UMZCH microcircuits, as well as malfunctions of the speaker speakers.

Consider repairing the music center Samsung MAX-VS720.

The malfunction manifests itself as follows: hoarse, distorted sound, both in the tuner mode, and in the CD / MP3 player, cassette deck, external AUX IN signal.

When connected to the center of knowingly serviceable speakers instead of relatives, it turned out that both acoustic speakers of the music center, as well as one output channel of the amplifier, were faulty. It was this channel that gave out a distorted, hoarse sound.

When checking the speakers, it turned out that one of them had a faulty full-range speaker - the voice coil was displaced. With light pressure on the speaker cone, you could hear the voice coil brushing against the walls of the magnet core. Mixing the voice coil with respect to the core is one of the common faults in electrodynamic loudspeakers.

Another column was also found to be faulty. The main speaker has a broken voice coil. Both faults (coil misalignment and breakage) are very difficult to repair. In this case, it is wiser to purchase speakers with similar parameters and replace the faulty ones.

Apparently, the cause of the malfunction was the long-term operation of the music center at maximum volume. This led to the failure of the speakers, followed by the failure of one of the amplifier channels.

When inspecting the printed circuit board in the area of the power amplifier, no burnt elements or damaged printed tracks were found. It was concluded that the audio frequency power amplifier (UMZCH) chip is faulty STK403-070.

Video (click to play).

To finally make sure that the STK403-070 microcircuit is malfunctioning, headphones were connected to the “Phones” jack. The sound in the headphones in all operating modes of the center was clean, without distortion, which confirmed the assumption that the STK403-070 microcircuit was defective, which is responsible for amplifying the stereo signal and outputting it to the speakers.

To dismantle a faulty UMZCH microcircuit, it is necessary to thoroughly disassemble the music center. When disconnecting flexible loops and wires connecting different units, you can mark connectors and loops with a marker or take a clear photo of all interconnects. This technique will help to avoid confusion during the subsequent assembly of the device.

Since the STK403-070 microcircuit is multi-pin, it is better to solder it using a desolder (desoldering pump). To remove the solder from the soldered pins of the microcircuit, you can also use a copper braid.

If there is no desire at all to mess around with the desoldering for a long time, then in turn we bite off the microcircuit conclusions with pliers as close as possible to the board. Then we unscrew the two bolts that attach the microcircuit to the aluminum radiator. Everything! Now we solder the new UMZCH microcircuit to the board.

We connect working sound speakers and test the device. We check the operation of the tuner, cassette deck, CD / MP3 - player, external input AUX IN.

It will be useful to clean the laser lens of the optical unit. As a rule, fine dust is deposited on the lens, which impairs reading from the disc. It is best to do this when you have some experience in repairing CD / MP3 players and radio tape recorders. Dust from the lens is erased with a regular cotton swab, making several light circular movements along the lens surface. Do not moisten a cotton swab with cleaning agents, the lens material may react with the cleaning agent and become coated.

In case of contamination of the elements of the tape drive mechanism of the cassette deck, we clean the magnetic head, tape drive rollers.

For these purposes, we use cleaning cotton swabs moistened with cologne. Do not use excessive force when cleaning the magnetic head. With a slight movement, move 2-4 times over the surface of the magnetic head. Remove brownish deposits and dust from rollers and tones in the same way.

Cleaning the lens and cassette deck is optional, but advisable, especially when a paid repair is required. Also, you should perform a general cleaning of the device from dust inside the device and dirt on the outer panel. Agree that the customer will be glad if he sees his device not only repaired, but also stylishly sparkling with cleanliness! This will raise your professionalism in his eyes, and he will definitely turn to you for repairs!

Troubleshooting Music Centers

The article describes how to eliminate the most likely malfunctions that occur in music centers and other similar household audio equipment: failures or malfunctions in reading CDs of the player, malfunctions of the volume control or LPM tape recorders with a reverse, malfunctioning power amplifiers and a power supply unit.

Being engaged in the repair of music centers of various companies (AIWA, JVC, LG, etc.), one has to deal with a number of the most frequent malfunctions, and regardless of the manufacturer. Although from experience we can say that the devices of more serious companies, such as MATSUSHITA, SONY, etc., are very reliable and fail much less often. Of course, many malfunctions arise through the fault of the user, due to careless handling of the device, however, there are a number of such faults, the reasons for which are related to the aging of parts and assemblies of the device itself, wear of rubber, oxidation of contacts, the presence of a layer of dust, etc.

The most common malfunction in most music centers is poor readability or complete read failure in an audio CD player (CD-DA). This is mainly due to contamination of the laser head, aging and, accordingly, deterioration of the transparency of the plastic lens. Malfunctions are expressed in the fact that the player tries to read the initial tracks of the CD for a long time and, finally, stops. Sometimes it is able to identify the disc and start playing, but it may often fail when playing music.

In case of such failures, first of all, it is necessary to check the operability of the laser itself and the transparency of the lens 3 (Fig. 1 shows a simplified drawing of the laser head), as well as the error correction device on the electromagnet 4. For this, it is enough to open and close the carriage without inserting a CD. music center player. The cover of the device itself, of course, must first be removed so that the laser head is visible. As soon as the carriage moves to its place and the rotor of the disk drive motor starts rotating, the lens on the laser head should move up and down using an electromagnet. Moreover, if you look at the lens from a certain angle, you can see a thin red laser beam. If all of the above processes are completed, the laser head is working properly. Sometimes it is enough to wipe the lens surface with a soft cloth to fix the malfunctioning of reading CDs. This should be done very carefully so as not to damage the lens or rip it off the mount on the electromagnet. If there is no improvement or it is insignificant, it is most likely that not only the lens is contaminated, but also the prism 2 under the lens (see Fig. 1). To clean the surface of the prism, remove the laser head from the device.

The lens and electromagnet are fixed to a metal plate 1. They can be covered with a small plastic snap-on cap.This cap must be removed, then unscrew the fastening screws 6, which press the metal plate to the base 5. Carefully lifting the plate, you can see a small hole under the lens. After winding a small piece of cotton wool on a match and dipping it in alcohol, wipe the surface of the prism. Then very carefully put in place the metal plate with the lens and screw it with screws 6. After that, close the electromagnet of the head with a protective plastic cap and set the head in place. A laser head cleaned in this way in most cases begins to read information normally from a rotating CD. If this does not help, then, most likely, the transparency of the lens has deteriorated or the laser diode is faulty and the laser head needs to be replaced with a new one.

In music centers with a tape recorder, in which there is an auto-reverse of the tape movement, some specific disturbances in the operation of the LPM of the tape recorder may occur. When you press the play button, the motor shaft starts to rotate, but after a few seconds it stops. In such cases, rewinding may work.

This malfunction occurs mainly due to the weakening of the belt tension between the engine pulleys and the drive shaft of the tape recorder. In most CVLs with autoreverse used in music centers, instead of a four-track head, a two-track head with a turning mechanism is installed. Rotating the head when reversing the direction of movement of the tape in the tape recorder requires a certain effort at the moment of switching. When the belt tension is weakened (due to rubber aging), the head rotation mechanism is jammed in any position and the CVL stops working. Such a malfunction can be easily eliminated by replacing the old belt with a new one.

Another malfunction that sometimes arises in digitally controlled devices that have worked for several years, manifests itself in the termination of volume control by a regulator located on the device itself; the volume control from the remote control is effective. Such failures arise because in such music centers, instead of ordinary variable resistors - volume controls, special sensors - knobs are installed, when rotating, the corresponding contacts close, and the processor, depending on the direction of rotation of the shaft, changes the gain in the path. If these contacts become dirty or oxidized, they will malfunction and disrupt the normal volume control.

Elimination of the malfunction consists in cleaning the knob contacts. Since it is located on the front panel of the device, disassemble the device. On the front panel of most music centers, there is a large printed circuit board, into which the volume encoder is soldered. After dismantling, it is disassembled by unbending the metal frame-mount, then the internal contact tracks are washed with alcohol, cleaned from the oxide with an eraser (eraser) and again washed with alcohol. Before assembly, the contact tracks are lubricated with a small amount of grease. A repaired rotary encoder will usually work normally for several more years.

Failure of a power amplifier in a music center often occurs due to careless handling - a short circuit of the amplifier output to a common wire or case. Since in most music centers power amplifiers are made on integrated microcircuits, the repair may consist in a banal replacement of the microcircuit with a serviceable one. However, there may be cases when it is difficult to find a similar microcircuit, especially where there are no shops selling imported radio components, and there is no way to stock up on a wide range of elements in advance. There are also cases when, as a result of the combustion of a microcircuit, the inscription on it has disappeared and it is not possible to determine the type of microcircuit.If the circuit of the device could not be found, the device can be repaired by using TDA1557 or TDA1552 instead of the burnt out microcircuit. These microcircuits differ in that they do not require any external elements for operation, and therefore replacing any integrated power amplifier with one of these microcircuits will require a minimum of work. The output power of these microcircuits - 2 × 22 W - corresponds to the majority of mid-priced music centers.

At the input 11 of the microcircuit (see Fig. 2), you need to send the Stand-By signal, which controlled the operation of the old microcircuit. It can be found as follows. Connecting in turn to the contact pads at the location of the old microcircuit, a voltmeter or an oscilloscope, turn on and off the music center with a button on the front panel and find a place where, when the center is off, the voltage is close to zero, and when it is on, to the supply voltage. If this signal cannot be found, then in extreme cases pin 11 (Fig. 2) can simply be connected to the positive power bus of the microcircuit.

I have changed the output amplifiers in JVC and Panasonic music centers (one of the MATSUSHITA brands). The results of this replacement of the output microcircuit turned out to be good. If the output power turns out to be slightly overestimated, then it can be reduced to the required level by cutting the tracks on the music center board in the input signal circuit in front of the coupling capacitors and soldering the resistive dividers shown in Fig. 3. By selecting resistors R1 and R3, they achieve the output power reproduced by the loudspeakers of the music center without distortion. It is unacceptable to exceed the output power more than the previous one, as this can lead to failure of the dynamic heads or the power supply of the music center. If you use surface mount resistors for R1 — R4, this modification can be done very carefully without spoiling the appearance of the board.

The described replacement of the power amplifier is also suitable for repairing UMZCH car radio tape recorders; it allows you to significantly increase the quality indicators and output power of an average quality car radio.

And finally, another malfunction, which is also common, is a defect in the mains transformer. If there is a circuit and known voltage values on the secondary windings of the transformer, this repair is not particularly difficult, but if this information is not available, problems may arise with replacing the transformer or rewinding it, especially if there are several secondary windings.

It is necessary to eliminate this malfunction, starting with checking the health of the power cord and fuses. If the fuses are turned on in the secondary circuits and the mains voltage comes directly to the primary winding of the transformer, and there is no voltage at its output, most likely the fuse is built into the transformer. This fuse is present in most transformers and is mounted over the primary winding, but other arrangements are possible. If this fuse is not present or it turns out to be intact, and there is an open in the primary winding, then the transformer will have to be changed or rewound accordingly. Rewinding the primary winding in the transformer from the music center is sometimes not easy. Firstly, the winding is filled with varnish, and the wire is thin and it turns out to be impossible to count the turns, gradually winding it up (the wire often breaks). Secondly, even knowing the number of turns, it is often not possible to lay them so tightly during winding as it was done at the factory, and as a result, the wound winding does not fit in the transformer frame or in the magnetic circuit window. Therefore, it is easier to find out what the secondary voltages should be, and wind up another transformer or pick up a ready-made one - since there is usually enough space inside the music center.

It is best to start clarifying the voltage values in the secondary winding circuits by looking for a circuit or any inscriptions about the voltages on the printed circuit board. If this is not the case, then you can try to determine the voltage using one of the microcircuits. Best of all - on the power amplifier microcircuit (having found out the nominal voltage of its supply from the reference book). As noted above, in most cases this voltage turns out to be in the range of 14. 17 V. Knowing it, one can accordingly assume what should be the voltage on the transformer winding. If, for example, the rated supply voltage of the microcircuit is 15 V, then due to the fact that after the diode bridge and filter capacitors the voltage increases by about 1.4 times (at low load), the transformer winding should be respectively 12-13 V. Then you can wind up all the secondary windings of the transformer and count their turns. Since the wire of the secondary windings is quite thick, it is not difficult to do this even with the windings filled with varnish. Knowing the number of turns of the windings and the voltage on one of them, it is no longer difficult to calculate the remaining voltages using the well-known formula

where U_N and U₂ - voltage, respectively, of unknown and known windings; w_N and w₂ - the number of turns of the corresponding windings.

When winding the windings of a new transformer, the wire diameter should be no less than that with which the windings of the old transformer were wound. Even if the voltage of the windings of the new transformer differs from the required by 1-2 V, this will not have a significant impact on the operation of the music center.

Each of the faults discussed in the article may require an individual approach, and the methods for their elimination may differ from those described by the author, however, I hope that the recommendations outlined here will help masters, especially beginners, when repairing music centers and other household audio equipment.

I. KOROTKOV, Bucha, Kiev region, Ukraine

The music center is designed to read media, listen to radio broadcasts. The receiver module is easy to find after disassembly for the presence of a thin metal (foil) shield. Inside the steel box: high frequency amplifier, local oscillator, mixer, other stages. Electronic microcircuits cannot be repaired, individual spare parts are more expensive than the device as a whole. Music centers use a superheterodyne circuit with one frequency conversion. The final cascade is a stereo low-frequency amplifier, through which sound passes to the speakers in the music center. Decoupling through transistor keys controlled by the position of the regulator on the front panel of the household appliance. Do-it-yourself repair of the music center is not always possible, it is interesting to see what is inside.

Let's try to see how to fix your Samsung Music Center yourself. A sensible technical description fell into the hands, we will read. We will leave the repair of Sony music centers for the next time. Radio receivers in music centers are wide-wave, and the creators did not bother too much with the circuit, they made two paths:

For AM modulation at mid and low frequencies.
For frequency modulation on VHF.

Avoid painting the intricacies of band dividing, just remember: small FM antennas receive a frequency modulated signal. Tracks can be performed on one microcircuit (like KA2295Q) and separately. Before the detector, both paths are incompatible due to the specifics of signal processing. You can amplify the weak one, mix it with the frequency of the local oscillator, do not interfere with the subtlety: each cascade of the Earth has a limited frequency band so far. We repeat, the paths go separately to the detector inclusive. The advantage of an integrated solution is described by a high specialization, automatic frequency control eliminates the worry of unreliable signal reception by the music center.

Many do not imagine a device that refuses to play cassettes. There are usually two decks, they work on reproduction alternately, controlled mechanically. At the circuit level, the amplifier switches to the desired head. The tape drive mechanism with one motor pulls the tape, the bobbins are slightly spring loaded. The recording-playback paths are separate, you can write:

cassette-cassette;
receiver-cassette;
laser disc reader-cassette.

Today, a chip for decrypting MP3 and other formats is being added. The stream enters the low frequency amplifier. It is not difficult to notice the microcircuit, the case is set under a solid radiator of solid dimensions. Here the lion's share of the energy consumed by the music center is lost, other stages operate with a low-amplitude signal.

Simultaneous playback from a tape recorder and a laser disc is not provided. Would make sense when mixing home author's recordings. The microphone works in all modes. Allows you to write on karaoke tape, sing along to artists on the radio.

The read-write preamplifiers are assembled by a single microcircuit, for example, K22291. The film erasure current is generated by a transistor generator. It is clear that the frequency differs greatly from the sound one. We must not forget about the software or microcircuit implemented equalizer. Simpler than a steamed turnip, a cascade that focuses on a selected part of the spectrum of the track being played. It is customary to listen to rock, pouring bass on neighbors, a low-pass filter makes a contribution.

The work of the drive of the laser discs is fueled by the controller, which is responsible for focusing, tracking the tracks. Samsung uses the KA9220 microcircuit, which controls the motors through the KA9258 drive unit and amplifiers. There are two drive motors, one rotates the disk, the second positions the head. The KA9220 controller runs the work, pre-decrypts the head signal. Further processing of the sound is carried out by the KS9282 signal processor, the waves are corrected and interpolated. To eliminate high-frequency interference, filtering is carried out with the KA9270 microcircuit.

There is always a system controller in the music center. A microcircuit that controls the operating modes of the equipment. Some Samsung music centers use MICOM LC866216 for this purpose. For interactivity, the controller is supplemented with an indication panel and keys. Through the interface, the user controls the music center. On the front panel there is a receiver for infrared radiation of the control panel. It is worth noting: the central controller analyzes the position of the volume knob, generates signals for adjusting the low-frequency amplifier (a microcircuit on a large radiator). The control bus is digital, so you should not look for a volume control on the transistor.

Switching power supply. It contains input signal filters, a high-frequency pulse generator that controls a key on a transistor, output filters, and sometimes Schottky diode rectifiers. The voltages are stabilizing. Transformer, fuses are carried out on a separate board. The device refuses to turn on - it is logical to start repairing the music center with your own hands from here. There are several supply voltages, be sure to ring the secondary windings.

Consider a receiver. In the case of Samsung music centers in the VHF range, the telescopic antenna signal comes to the preselector (a set of resonant channel filtering circuits plus a high-frequency amplifier). A typical circuit follows: mixer with local oscillator, detector. The restructuring of the circuits is carried out by varicaps using the voltage of the automatic frequency control chip of the LM7000 music center. For smoothing, the signal is filtered before being fed to the varicaps. The receiver local oscillator frequency is controlled by the LM7000 microcircuit. The signal selection is carried out mainly in the intermediate frequency amplifier. Before it, the frequency jumps, here it takes on a fixed value (10.7 MHz).Consequently, piezoceramic filters are easier to set up.

The KA2295Q microcircuit, mentioned above, is represented by a combination of an amplitude and frequency detector and separates the useful signal from the carrier. This includes the medium, long wave path. Including LOs, mixers, amplifiers. The first stage is equipped with automatic gain control. For the correct operation of the frequency detector of the music center, a phase-shifting oscillatory circuit is required. Automatic gain control works on a signal from the mixer. It is necessary that the intermediate frequency amplifier and the frequency converter do not go into cut-off mode.

From the FM detector through a filter, the signal is fed to the stereo decoder pilot tone. Information about the presence of a stereo signal is sent to the central controller. You can select the mode by the controller forcibly. The central controller of the music center receives information about the signal state, controls the formation of sound. The channels are balanced by means of a variable resistor. The filtered signal goes to the TDA 7318 microcircuit, where the cascade of the main low-frequency amplifier of the music center begins.

In the MW and LW ranges, loop antennas with transformer coupling are used. The music center device includes band switching transistors. The heterodyne switches are switched as required by electronic keys. The adjustment is carried out by varicaps, the adjustment is made according to the AFC signals. The high-frequency amplifier is a broadband amplifier, it is not commutated in the music center. The intermediate frequency in the MW and LW bands is 450 kHz (typical). The detected signal, without passing through the pilot-tone scheme, is immediately fed to the filters to the output amplifier of the receiver. As for the MW and LW, the circuit communicates with the central controller of the music center about the fact of frequency capture, which helps the "brain" to keep abreast of events.

It remains to add, there are two channels, just at FM frequencies the sound is different, on DV and MW it is the same. What is called, in fact, stereo and mono. When reading cassettes, discs, a similar situation, you can artificially bring separate playback to continuous. The differences between the channels of the music center are leveled.

It is important to understand that the main types of faults can be represented by a careful study of the diagram. The review did not contain a complete and complete description of the musical center, we will return to this. The master must know in advance what will break. Self-repair of music centers will seem like child's play.

Always look for original factory diagrams, descriptions, before digging into the electronic guts of household appliances. The drawings of the microcircuits are open to free access by the copyright holders. The purpose of the chips is described on the websites of the manufacturers.

The main components of the music center. Causes of malfunctions of components of the music center. Troubleshooting Algorithm. Councils for the operation of music centers.

Most people who are just beginning music lovers do not risk getting into electronic devices once again, such as stereos, for example, or CD / MP3 players, computers, laptops, etc. In principle, they are doing everything right, because if you do not know how the device works, then you can not only fix it, but also break it.

In fact, most breakdowns can be repaired with your own hands. This does not require any special knowledge there. Most breakdowns occur so often that it only takes a few minutes to identify the breakdown.

For the reason that the nature of breakdowns is completely different, it is impossible to consider everything in one publication. We will consider the most common malfunctions of music centers associated with high-quality sound reproduction.

No sound in any operating mode.
Interference, bass, unpleasant sounds in any operating mode.
There is no sound from one of the speakers.
Periodic disappearance of sound.

In order to fix one of the breakdowns, you first need to check the operation of the speakers (speakers). Connect any other speaker (from the old system) that has an impedance of 4-8 ohms. All amplifiers in music systems are designed for this impedance. In order not to be mistaken, check the resistance value on the back of the case, where the connection connectors are.

Do not skip the check if you have not found a column of the required resistance. Suppose a 6 ohm resistance load is indicated on the body of the music system, and you have found an old 4 or 8 ohm speaker. Do not despair, such a column is quite suitable for testing. The main thing to remember is that you cannot connect speakers with very low impedance (less than 2 ohms).

So, first we connect a working speaker or speaker to the music center and listen to how it works with it. If, as a result of this check, all the breakdowns have disappeared, then this means that the speakers are defective, and they must be returned for repair. If the malfunction has not disappeared, then this means that you need to repair the music center itself. Columns have nothing to do with it.

Wheezing, noise, interference, complete absence of sound, intermittent lack of sound may appear due to a violation of the connection of the contact connector and contact copper tracks, which are located on the main board of the system. This breakdown is associated with intensive device operation or soldering degradation.

First you need to disassemble the music center and scrupulously consider all the contact connections and the soldering of the output connector, to which the speakers are connected. Fortunately, broken contacts and soldering are immediately noticeable. To prevent possible future malfunctions, solder the connector pins. This will prevent degradation of the solder.

If there is a degradation of the soldering around the contact, which is sealed into the board, then a more or less visible gap is immediately formed. It is he who interferes with the contact of the printed track and the copper contact. Solder degradation is associated with mechanical stress. Overheating occurs at the location of the soldering. This phenomenon occurs very often in old systems that have been in operation for more than one year. It is necessary to make sure that the breakdown is associated with the final audio path.

First, you need to check the operation of the device in all possible modes that are provided in the music center you purchased. If breakdowns appear in all operating modes, then the malfunction is located precisely in the amplification output path. This means that the audio frequency power amplifier microcircuit (UMZCH) is faulty. Another part of the system may also be broken - a sound processor chip or signal switching.

There is a chance to get confused and look for breakdowns in the wrong place. In this case, you need to take the most ordinary headphones and connect them to the Phone jack. This connector is available on all music systems. Just remember to turn the volume down before doing this.

Further, in turn, you need to try all the operating modes of the center. The serviceability of the sound path to the UMZCH is checked by ear. Performing this action immediately narrows the search for a breakdown. After all, if you hear clear sound in the headphones, it means that all the nodes of the audio path are working correctly (including the processor, switch, amplifiers). The malfunction is most likely associated with the part of the electronic circuit that is responsible for the amplification and signal strength.

If, after all these operations, the malfunction still remains, then the UMZCH microcircuit is broken. There are times when the microcircuit works only halfway. This means that only one of the two output channels works. One of these channels can handle noise and interference. In this case, the microcircuit can work for a very long time.

The main thing to remember is that when searching for breakdowns, the most important thing is to narrow the search area. Don't jump to conclusions.In principle, the procedure for repairing electronic systems is as follows:

initial inspection of the apparatus;
functionality check;
testing the operation of the device in all modes.

It is necessary to assess the malfunction of a specific individual unit of the system. This includes: tuner box, control panel, CD / MP3, amplifiers, power supply.

Next, you need to carefully examine the electronic board to identify all burned-out tracks, radioelements, cracks, degradation, deformation of microcircuits.

The device is a typical audio combine - single-cassette deck, CD-ROM and digital tuner. All this is controlled by buttons, and information is displayed on the LCD screen. Unfortunately, there were no speakers - obviously the workers took them with them.

We disassemble the center and start repairing.

The freebie in the form of a torn power cord or a blown fuse did not work, but after a long and careful examination, one of the rectifier diodes was found to be missing - there is voltage at the input of the diode bridge, and zero at the output.

Having restored the malfunction of the power supply, it was possible to get the first sounds from the music center, but what it receives there and what modes are, it is not clear - the backlight lamps of the LCD display burned out.

Now we remove the front part of the center and unscrew the board with the control buttons. It contains a small indicator of the current state of operation, the frequency of the FM receiver and the sound volume.

Pulling back the glass display reveals a pair of miniature incandescent bulbs behind it. There is a 12V supply voltage on their contacts, but they still do not light up.

We solder and replace with others. It is even better to put LEDs, then the backlighting will become almost eternal, but in this case, made it as simple as possible.

So that the situation with the burnout of the light bulb does not happen again, I put a current-limiting resistor for a couple of tens of Ohms on the backlight power supply.

The tape drive mechanism of the cassettes has long been damaged, and since it is not important to repair it (this is not a rare record player), I simply unscrewed it, disconnected the cables with wires and threw it away.

And the lid itself, which covers the cassette, was simply screwed to the body with aluminum plates.

You can collect the refurbished music center back and test it. It works great, the backlight glows normally, and the sound is noticeably superior to simple amplifiers of computer speakers on cheap TDA-shkakh.

For testing, he connected 50-watt home-made speakers to the center, which he easily swung. The repair can be considered complete.

Posted by admin in Household appliances 29.08.2018 0 55 Views

For AM modulation at mid and low frequencies.
For frequency modulation on VHF.

cassette-cassette;
receiver-cassette;
laser disc reader-cassette.

Consider a receiver.In the case of Samsung music centers in the VHF range, the telescopic antenna signal comes to the preselector (a set of resonant channel filtering circuits plus a high-frequency amplifier). A typical circuit follows: mixer with local oscillator, detector. The restructuring of the circuits is carried out by varicaps using the voltage of the automatic frequency control chip of the LM7000 music center. For smoothing, the signal is filtered before being fed to the varicaps. The receiver local oscillator frequency is controlled by the LM7000 microcircuit. The signal selection is carried out mainly in the intermediate frequency amplifier. Before it, the frequency jumps, here it takes on a fixed value (10.7 MHz). Consequently, piezoceramic filters are easier to set up.