Do-it-yourself music center repair does not turn on

Many novice radio amateurs are sometimes afraid to repair complex electronic devices such as music centers, CD / MP3 players, computers. This is due to uncertainty, because if you have little experience, then you can not only not fix the device, but even break it ...

But in fact, most of the malfunctions of complex devices are quite easy to repair and you do not need to have a lot of experience to fix them. Many faults are generally so common in repair practice that sometimes 5 minutes is enough to diagnose the malfunction and in 95% cases to say what exactly is faulty!

Since malfunctions are different, and it is impossible to cover everything in one article, we will consider the most common breakdowns of music centers - malfunctions associated with amplification and high-quality sound reproduction.

Let's consider examples of faults:

No sound in any operating mode (tuner, cassette deck, CD / MP3 player, external signal)

Husky, unpleasant playback sound in any operating mode.

There is no sound from one of the speakers (speakers).

The sound from time to time disappears, appears.

To eliminate any of these faults, you must first check the health of the speakers (speakers). To do this, you need to connect another speaker or a speaker with an impedance of 4 - 8 ohms. The speaker can be taken from an old faulty TV, tape recorder.

Usually all amplifiers of musical centers are designed for load resistance (speakers, speakers) in the region of 4-8 ohms. This value is indicated on the back of the device near the speaker connectors.

Do not ignore the check if you do not have a speaker for the required impedance. For example, on the case of the music center it is written that the load should be 6 ohms, and you only have a speaker for 8 or 4 ohms. Nothing wrong! You can connect one for testing, it is only important not to connect speakers with a very low internal impedance, less than 2 ohms.

So, you need to connect a known working speaker or column and listen to how the music center works with a working speaker.

If, when connecting a working speaker, the malfunction disappeared, then the speakers are damaged, and you will have to repair them. If the malfunction persists, then it is necessary to repair the device itself, and not the external speakers.

Wheezing, no sound, sudden disappearance / appearance of sound may be due to the fact that the connection of the output connector and contact copper tracks on the main board of the music center is broken. This malfunction is associated with intensive use of the device or degradation of soldering.

It is necessary to disassemble the center and carefully inspect the contact connections, the soldering of the output connector to which the speakers are connected.

Defective contact and soldering is visible to the naked eye. Just in case, it is better to solder the connector contacts, as soldering degradation is possible.

With the degradation of the soldering around the contact soldered into the board, a slightly visible gap is formed, non-soldering, which interferes with the reliable contact of the printed track and the copper contact. The appearance of soldering degradation is associated with mechanical stress, overheating at the soldering point, “fatigue” of the metal and is found mainly in rather old devices that have operated for more than one year.

To rule out the situation: “I was looking in the wrong place… ”Let's make sure that the malfunction is connected with the final sound path of the music center.

First, we check the operation of the device in all modes - tuner (receiver), cassette deck, CD / MP3 player, external input AUX IN.

If a malfunction manifests itself in all modes, then the amplification output path is faulty, most likely the UMZCH microcircuit (Havebooster Mpower Zsonic Hfrequency). But it is possible that another unit of the device is faulty, for example, a sound processor chip, signal switching.

So you can get confused and look for a malfunction in the wrong place. In such cases, we take ordinary headphones and connect to the jack Phone (headphones), which all music centers have. Don't forget to turn down the volume before doing this!

In turn, we turn on all modes of operation of the music center and check by ear the health of the sound path to the UMZCH. With this simple operation, we narrow the area of ​​troubleshooting, since if there is undistorted and clear sound in the headphones, then all the nodes of the audio path, including the sound processor, signal switch, preamplifiers, are in good order and the malfunction is associated with that part of the electronic circuit that is responsible for the amplification and signal power ...

So, if after the actions taken, the malfunction persists, then the UMZCH microcircuit is most likely faulty. In the practice of repair, there are cases that the microcircuit is half operational. What does half mean? This means that, for example, 1 out of 2 output audio channels works. Or one of the amplification channels works with audible distortions. In such cases, the amplifier microcircuit can work for quite a long time.

Here are just a few real-world examples:

Chip TDA8588J. 4 - channel UMZCH with built-in power stabilizers.

After the wrong supply voltage to the car radio, 2 amplification channels work flawlessly, 1 channel noticeably “bass”, 1 channel produces a monotonous low-frequency hum instead of sound. On the face of a partial failure of the microcircuit. Despite a partial malfunction, the car radio is working properly, 2 serviceable channels are involved.

Microcircuit STK403-070. 2 - channel UMZCH. One of the amplification channels reproduces sound with distortion. The second channel is operating normally.

When searching for a malfunction, the main task is to narrow the search area for this very malfunction, so there is no need to rush to conclusions. The sequence of actions for repairing electronics is approximately as follows:

External examination of the device, checking the functionality, operation of the device in different modes.

An approximate estimate of the malfunction of a specific unit of the device: tuner unit, control panel, cassette or CD / MP3 deck, amplifier, power supply.

Inspection of the electronic printed circuit board in order to identify burnt-out tracks, "swollen" electrolytic capacitors, darkened and burnt-out radioelements, cracks on the board, non-soldering, deformation of the microcircuit cases.

Finding a faulty element using the described methods and replacing it.

Do not try to re-solder the entire PCB right away the repaired device, this will take your time and will contribute to the emergence of new faults caused by you. Remember, a professional radio mechanic solders two times: the first time - he solders the defective part, the second - solders the defective part... This is the ideal of repair that every radio mechanic should strive for.

To confirm what has been said, let us consider step by step the repair of the Samsung MAX-VS720 music center.

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 starts to read information normally from a rotating CD. If this does not help, then, most likely, the transparency of the lens has worsened 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. Rotation of the head when reversing the direction of movement of the tape in the tape recorder requires a certain effort at the time 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, you should 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, lubricate the contact tracks with a small amount of grease. A refurbished 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 the 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 the voltage should be 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

Musical centers have long and firmly merged into our lives. Many people are so used to music at their celebrations that they cannot imagine a holiday without their favorite music. And some people also became attached to their music centers, which served them faithfully for many years.

Due to a fairly simple device, this technique can work for years without breaking. But nothing can work forever. Personally, my opinion is that if the equipment has worked for 3-4 years without breakdowns, this means there is no point in throwing it away and running to buy a new one. You can try to repair your favorite device, and it can serve you as much more.

Of course, there can be problems with the mechanical part of the device. Over time, the plastic from which the gears are made "dries up". And since the production of our device ended many years ago, the gears are unlikely to be found on sale. But you can try to find people who are engaged in the manufacture of plastic or metal products. With apiaries, the situation is simpler. They are still used in many devices today. Therefore, acquiring them is not as difficult as gears.

There are also problems with “not soldered” element legs. Since tin is also subject to time. This often happens from vibration, but there are different reasons for this defect. In this article, we will tell you about one of such defects in music centers, and how to repair it with our own hands at home. To repair the music center, we need a Phillips screwdriver and a soldering iron.

The repair will be carried out on the example of the music center LG FFH-DV55AX. So, when you wiggle the AUX wires, the sound disappears. First, we check the wire, call or connect a known worker. After connecting another wire, the problem remained. Next, you should check the connector. To do this, you need to disassemble the music center. The photos below show the screws you need to remove to disassemble the LG Music Center case and repair it yourself.

The following photo shows cracks in the soldering area of ​​the AUX connector. This is the reason why the sound disappeared on the LG Music Center. We solder the connector, give a signal and check. The sound appeared. The LG Music Center issue has been fixed. We collect the device.

As you can see, this repair can be done by hand and without any difficulties.

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Is your TV, radio, mobile phone or kettle broken? And you want to create a new topic about this in this forum?

First of all, think about this: imagine that your father / son / brother has an appendicitis pain and you know from the symptoms that it is just appendicitis, but there is no experience of cutting it out, as well as the tool. And you turn on your computer, access the Internet on a medical site with the question: "Help to cut out appendicitis." Do you understand the absurdity of the whole situation? Even if they answer you, it is worth considering factors such as the patient's diabetes, allergies to anesthesia and other medical nuances. I think no one does this in real life and will risk trusting the life of their loved ones with advice from the Internet.

The same is in the repair of radio equipment, although of course these are all the material benefits of modern civilization and in case of unsuccessful repairs, you can always buy a new LCD TV, cell phone, iPAD or computer. And for the repair of such equipment, at least it is necessary to have the appropriate measuring (oscilloscope, multimeter, generator, etc.) and soldering equipment (hairdryer, SMD-hot tweezers, etc.), a schematic diagram, not to mention the necessary knowledge and repair experience.

Let's consider the situation if you are a beginner / advanced radio amateur who solders all sorts of electronic gizmos and has some of the necessary tools. You create an appropriate thread on the repair forum with a short description of “patient symptoms”, ie. for example “Samsung LE40R81B TV does not turn on”. So what? Yes, there can be a lot of reasons for not switching on - from malfunctions in the power system, problems with the processor or flashing firmware in the EEPROM memory.
More advanced users can find the blackened element on the board and attach a photo to the post. However, keep in mind that you replace this radio element with the same one - it is not a fact that your equipment will work. As a rule, something caused the combustion of this element and it could “pull” a couple of other elements along with it, not to mention the fact that it is quite difficult for a non-professional to find a burned-out m / s. Plus, in modern equipment, SMD radio elements are almost universally used, soldering which with an ESPN-40 soldering iron or a Chinese 60-Watt soldering iron you risk overheating the board, peeling tracks, etc. The subsequent restoration of which will be very, very problematic.

The purpose of this post is not any PR of repair shops, but I want to convey to you that sometimes self-repair can be more expensive than taking it to a professional workshop. Although, of course, this is your money and what is better or more risky is up to you.

If you nevertheless decide that you are able to independently repair the radio equipment, then when creating a post, be sure to indicate the full name of the device, modification, year of manufacture, country of origin and other detailed information. If there is a diagram, then attach it to the post or give a link to the source. Write down how long the symptoms have been manifesting, whether there were surges in the supply voltage network, whether there was a repair before that, what was done, what was checked, voltage measurements, oscillograms, etc. From a photo of a motherboard, as a rule, there is little sense, from a photo of a motherboard taken on a mobile phone there is no sense at all. Telepaths live in other forums.
Before creating a post, be sure to use the search on the forum and on the Internet. Read the relevant topics in the subsections, perhaps your problem is typical and has already been discussed. Be sure to read the article Repair strategy

The format of your post should be as follows:

Topics with the title “Help fix the Sony TV” with the content “broken” and a couple of blurred photos of the unscrewed back cover, taken with the 7th iPhone, at night, with a resolution of 8000x6000 pixels are immediately deleted. The more information about the breakdown you put in a post, the more chances you will get a competent answer. Understand that the forum is a system of gratuitous mutual assistance in solving problems and if you are dismissive of writing your post and do not follow the above tips, then the answers to it will be appropriate, if anyone wants to answer at all. Also note that no one should answer instantly or within a day, say, no need to write after 2 hours “That no one can help”, etc. In this case, the topic will be deleted immediately.
You should make every effort to find a breakdown on your own before you get stuck and decide to go to the forum.If you outline the whole process of finding a breakdown in your topic, then the chance of getting help from a highly qualified specialist will be very great.

If you decide to take your broken equipment to the nearest workshop, but do not know where, then perhaps our online cartographic service will help you: workshops on the map (on the left, press all buttons except “Workshops”). You can leave and view user reviews for workshops.

For repairmen and workshops: you can add your services to the map. Find your object on the map from the satellite and click on it with the left mouse button. In the field “Object type:” do not forget to change to “Equipment repair”. Adding is absolutely free! All objects are checked and moderated. A discussion of the service is here.

It just so happens that equipment that has served well for a long time or, conversely, bought not so long ago, suddenly stops working. But this does not mean at all that it can no longer be restored.

Before you know how to repair a music center, you should determine the cause of its breakdown.

Repair of the music center may be required for the following reasons:

• the end of the working life of the parts, which is provided by the manufacturer;
• mechanical impact - equipment falling to the floor, impacts, etc .;
• the use of low-quality CDs;
• failure of the power supply and electronic boards due to voltage drops in the electrical network;
• an independent attempt to disassemble the equipment for the purpose of cleaning;
• the use of memory drives with questionable content (in terms of the presence of viruses).

But this is far from the whole list of possible problems, but the most common ones; in all other variants, special cases are possible that require only specialized diagnostics.

It is important! Regular cleaning and lubrication of equipment mechanisms is a prerequisite for the long-term operation of any equipment.

The most common "disease" of this equipment is the refusal to read discs. As a rule, in this case, a complete replacement of the laser optics will be required.

Crash during CD playback often occurs due to contamination of the optical system, or rather dusty lens. In this case repair of the music center Sony or any other will be limited to wiping its surface with cotton wool, and an even better option is to blow off the dust using a special aerosol can with compressed purified air.

Is the disc spinning? The problem is most likely in the drive microcircuit or in the engine itself, which is solved as follows: remove the entire drive and unsolder the board. If the disk spins, but slowly, and at the same time the driver microcircuit heats up, there is probably a short circuit in the motor winding.

If the CD is spinning but not readable and LOAD is displayed on the display, repair of the music center, whether Aiwa, Sony, Panasonic or Samsung, will consist in replacing the laser head. But the master will also check the flexible cable; problems with it are also possible - in the places of inflection near the laser.

If the indicator does not light up when you turn on the tape recorder, and the check shows that the voltage from the power supply is lower than required, most likely the reason is in the electrolyte of the power supply filter. However, the reason, perhaps, lies in the failure of the power supply due to deformation of the output microcircuits in the ULF.

Equipment failure can be associated with cheap pirated CDs. In addition to the fact that information is sometimes not read from them, they can lead to the destruction of both the disks themselves and the elements of the reader.

If the clock does not work, or there is no reception of the tuner in the FM range, then the basis for repairing the music center may be: a malfunction of the controller microcircuit, quartz, stabilizing the generator frequency in the microcircuit.

First of all, it is worth excluding all negative factors from the process of using the equipment, such as: mechanical stress, poor-quality discs, voltage drop (it is recommended to use a stabilizer), self-repairs, etc.

In addition, you need to take care of the external panels of the equipment without the use of abrasive and caustic agents, refrain from installing equipment near heating devices, and avoid getting any liquid or foreign objects into the DVD tray.

First of all, the specialist of the service center makes a complete diagnostics of the equipment.

According to statistics, difficult repair of music centers required only in extreme cases, in more than 50% of the work is limited to general cleaning and adjustment of the main components of the device. But at the same time, it should be borne in mind that one of the main reasons for unnecessary material costs is contacting non-professional craftsmen.

And the availability of the services of the most common parts in stock (microprocessors, electronic boards, drive motors, gears, laser optical devices, volume controls, power supply transformers, etc.) guarantees a fast repair of music centers Samsung, Panasonic, Aiwa, Sony and other well-known models.

List of services provided:

• repair of remotes, tuner, tape recorder, turntable, tape-pulling mechanism, mechanism after ingress of liquid, consequences of mechanical damage;
• restoration of the main board, reading system;
• troubleshooting laser head, cassette deck, electronics, power circuits, control processors, etc.

In case of any problems, you can always contact the specialists, they will conduct repair of musical centers in Novosibirsk quickly and inexpensively.

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 LCD backlight lamps 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.

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 starts to read information normally from a rotating CD. If this does not help, then, most likely, the transparency of the lens has worsened 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. Rotation of the head when reversing the direction of movement of the tape in the tape recorder requires a certain effort at the time 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, you should 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, lubricate the contact tracks with a small amount of grease. A refurbished 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 the extreme case, pin 11 (Fig.2) you can simply connect 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 the 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 the voltage should be 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 UН and U2 are the voltage, respectively, of the unknown and known windings; wН 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