Music centers have long been firmly integrated into our lives. Many people are so accustomed to music at their celebrations that they cannot imagine a holiday without their favorite music. And some people also became attached to their musical centers, which served them faithfully for many years.
Due to its fairly simple design, this equipment can work for years without breaking down. But nothing can work forever. My personal 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 out to buy a new one. You can try to repair your favorite device, and it can serve you just as long.
Of course, problems may arise with the mechanical part of the device. Over time, the plastic from which the gears are made dries out. 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 make products from plastic or metal. The situation with apiaries is simpler. They are still used in many devices. 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 due to vibration, but there are different reasons for this defect. In this article, we will tell you about one of these defects in music centers, and how to repair it with your own hands at home. To repair the music center we will need a Phillips screwdriver and a soldering iron.
We will carry out the repair using the example of the LG FFH-DV55AX music center. So, when the AUX wires are moved, the sound disappears. First, we check the wire, call or connect a wire that is known to work. 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 that need to be removed in order to disassemble the body of the LG music center and repair it yourself.
The following photo shows that cracks were found in the solder area of the AUX connector. This is the reason why there is no sound on the LG music center. We solder the connector, apply a signal and check. The sound appeared. The problem with the LG music center has been resolved. We assemble the device.
As you can see, this repair can be done with your own hands and without any difficulties.
Thank you for your attention and good luck with the repair!
Troubleshooting music centers
The article describes ways to eliminate the most likely malfunctions that occur in music centers and other similar household audio equipment: failures or malfunctions in reading CD players, malfunctions in the volume control or tape recorders with reverse, malfunctions of power amplifiers and the mains power supply.
When repairing music centers from various companies (AIWA, JVC, LG, etc.), you have to deal with a number of the most common malfunctions, regardless of the manufacturer. Although from experience we can say that devices from 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, but there are a number of those whose causes are related to the aging of parts and components of the device itself, wear of rubber, oxidation of contacts, the presence of a layer of dust, etc.
The most common malfunction of most music centers is deterioration in data reading or complete read failure in an audio CD player (CD-DA). This mainly occurs due to contamination of the laser head, aging and, accordingly, deterioration in the transparency of the plastic lens. Malfunctions are expressed in the fact that the player tries for a long time to read the initial tracks of the CD and, in the end, stops. Sometimes it manages to identify the disc and start playing, but there may be frequent failures while the music is playing.
In case of such failures, first of all, you should check the serviceability 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. To do 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 into place and the disk drive motor rotor begins to rotate, the lens on the laser head should move up and down using an electromagnet. At the same time, if you look at the lens from a certain angle, you will notice a thin red laser beam. Completion of all the above processes indicates that the laser head is working properly. To eliminate problems with reading CDs, sometimes it is enough to wipe the surface of the lens with a soft cloth. This should be done very carefully so as not to damage the lens or tear it off the electromagnet mount. If there is no improvement or it is insignificant, it is most likely that not only the lens is dirty, but also prism 2 located under the lens (see Fig. 1). To clean the prism surface, it is necessary to remove the laser head from the device.
The lens and electromagnet are fixed on metal plate 1. They can be covered with a small plastic cap with latches. This cap must be removed, then unscrew the fastening screws 6, which press the metal plate to the base 5. By carefully lifting the plate, you can see a small hole under the lens. Wrap a small piece of cotton wool around a match and dip it in alcohol, wipe the surface of the prism. Then very carefully put the metal plate with the lens in place and screw it in with screws 6. After this, close the head electromagnet with a protective plastic cap and put the head in place. In most cases, the laser head cleaned in this way 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 tape recorder may occur. When you press the play button, the motor shaft starts to rotate, but stops after a few seconds. In such cases, rewinding may work.
This malfunction occurs mainly due to weakening of the belt tension between the engine pulleys and the drive shaft of the tape recorder. In most CVLs with auto-reverse, used in music centers, instead of a four-track head, a two-track head with a rotation mechanism is installed. Rotation of the head when reversing the direction of movement of the tape in the tape recorder requires a certain force at the moment of switching. When the belt tension weakens (due to aging of the rubber), the head rotation mechanism gets stuck 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, which sometimes occurs in digitally controlled devices that have been in operation for several years, manifests itself in the cessation of volume control by the regulator located on the device itself; In this case, volume adjustment from the remote control is valid. Such failures arise because in such music centers, instead of the usual variable resistors - volume controls, special sensors are installed - valcoders, the rotation of which closes the corresponding contacts, and the processor, depending on the direction of rotation of the shaft, changes the gain in the path. When these contacts become dirty or oxidized, malfunctions occur and normal sound volume control is disrupted.
Troubleshooting involves cleaning the encoder 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 a valcoder is soldered - a volume control. After dismantling, it is disassembled by straightening the metal frame-mount, then the internal contact tracks are washed with alcohol, they are cleaned of oxide with an eraser (eraser) and washed again with alcohol. Before assembly, lubricate the contact tracks with a small amount of lubricant. A repaired encoder will usually work fine for several years.
Failure of a power amplifier in a music center often occurs due to careless handling - shorting the amplifier's output to a common wire or housing. Since in most music centers the power amplifiers are made on integrated circuits, repairs may consist of simply replacing the microcircuit with a working one. However, there may be cases when it is difficult to find a similar microcircuit, especially where there are no stores selling imported radio components, and it is not possible to stock up on a wide range of elements in advance. There are also cases when, as a result of the combustion of the microcircuit, the inscription on it has disappeared and it is not possible to determine the type of microcircuit. If the circuit diagram for the device cannot be found, you can repair the device by using a TDA1557 or TDA1552 chip instead of a burnt one. These microcircuits are distinguished by the fact 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 chips - 2x22 W - corresponds to most mid-priced music centers.
Before installing a TDA1557 or TDA1552 microcircuit instead of a faulty one, first of all, check that the supply voltage in the music center matches the supply voltage of the microcircuit itself. As a rule, it does not exceed 15... 17 V, which is quite suitable. In the absence of a music center circuit, use an oscilloscope to find which pins of the microcircuit receive the input signal. Having turned on playback from a CD or cassette and set the volume control to maximum, touch the oscilloscope probe one by one to the contact pads at the location of the old microcircuit. Having found the signal circuits, you should evaluate the signal amplitude and, depending on this, use the TDA1557 microcircuit (the sensitivity of its amplifiers is high - 50... 100 mV) or TDA1552 (with signal amplitudes up to 250...500 mV). Please note that input signals to the microcircuit must be supplied through isolation capacitors located on the board. The circuit diagram for connecting the microcircuits is shown in Fig. 2. As can be seen from the diagram, only the power and input signal of both channels are supplied to the TDA1557 (TDA1552), and the load is connected directly to the output pins. The microcircuit is mounted on a heat sink installed on the board; wires are soldered to its terminals, which connect them to the board. Various attachments used with the old microcircuit do not need to be removed.
At input 11 of the microcircuit (see Fig. 2), you need to apply the Stand-By signal, which controlled the operation of the old microcircuit. It can be found as follows. By connecting a voltmeter or an oscilloscope to the contact pads in turn at the location of the old microcircuit, turn the music center on and off with the button on the front panel and find a place where, when the center is turned off, the voltage is close to zero, and when it is on, it is close to the supply voltage. If this signal cannot be found, then, as a last resort, pin 11 (Fig. 2) can simply be connected to the positive power bus of the microcircuit.
I had the opportunity to change output amplifiers in JVC and Panasonic music centers (one of the MATSUSHITA brands). The results of such a replacement of the output microcircuit turned out to be good. If the output power turns out to be slightly too high, then it can be reduced to the required level by cutting the tracks on the music center board in the input signal circuit before the separating capacitors and soldering in the resistive dividers shown in Fig. 3. By selecting resistors R1 and R3, we achieve output power reproduced by the speakers of the music center without distortion. It is unacceptable to exceed the output power more than before, as this can lead to failure of the dynamic heads or the power supply of the music center. If you use surface mount resistors as 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 radios; it allows you to significantly improve the quality indicators and output power of an average quality car radio.
And finally, another malfunction, which also occurs quite often, is a defect in the network transformer. If you have a diagram and know the 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.
This malfunction must be eliminated, starting with checking the serviceability of the power cord and fuses. If fuses are included in the secondary circuits and the mains voltage comes directly to the primary winding of the transformer, but 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 on top of the primary winding, but other options for its location are possible. If this fuse is missing or it turns out to be intact, but there is a break in the primary winding, then the transformer will have to be changed or rewinded accordingly. Rewinding the primary winding in a transformer from a music center is sometimes difficult. Firstly, the winding is covered with varnish, and the wire is thin, and it turns out to be impossible to count the turns while gradually winding it up (the wire often breaks). Secondly, even knowing the number of turns, it is often not possible to lay them as tightly when winding as was done at the factory, and as a result, the wound winding does not fit into the transformer frame or in the magnetic circuit window. Therefore, it is easier to find out what the secondary voltages should be and wind another transformer or select a ready-made one - fortunately, there is usually enough space inside the music center.
It is best to start clarifying the voltage values in the secondary winding circuits by searching for a diagram or any voltage labels on the printed circuit board. If this is not the case, then you can try to determine the voltage using one of the microcircuits. The best way is to look at the power amplifier microcircuit (find out the rated voltage of its supply from a reference book). As noted above, in most cases this voltage is within 14... 17 V. Knowing it, we can accordingly assume what the voltage on the transformer winding should be. 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 approximately 1.4 times (at low load), the transformer winding should have 12-13 V, respectively. 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, this is not difficult to do even with varnished windings. 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
U N = w N. U 2 /w 2
where U N and U 2 are the voltage of the unknown and known windings, respectively; w N and w 2 - the number of turns of the corresponding windings.
When winding the windings of a new transformer, the diameter of the wires 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 malfunctions discussed in the article may require an individual approach, and the methods for eliminating them may differ from those described by the author, but I would like to hope that the recommendations outlined here will help craftsmen, especially beginners, when repairing stereos and other household audio equipment.
I. KOROTKOV, Bucha village, Kyiv region, Ukraine
Troubleshooting music centers
The article describes ways to eliminate the most likely malfunctions that occur in music centers and other similar household audio equipment: failures or malfunctions in reading CD players, malfunctions in the volume control or tape recorders with reverse, malfunctions of power amplifiers and the mains power supply.
When repairing music centers from various companies (AIWA, JVC, LG, etc.), you have to deal with a number of the most common malfunctions, regardless of the manufacturer. Although from experience we can say that devices from 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, but there are a number of those whose causes are related to the aging of parts and components of the device itself, wear of rubber, oxidation of contacts, the presence of a layer of dust, etc.
The most common malfunction of most music centers is deterioration in data reading or complete read failure in an audio CD player (CD-DA). This mainly occurs due to contamination of the laser head, aging and, accordingly, deterioration in the transparency of the plastic lens. Malfunctions are expressed in the fact that the player tries for a long time to read the initial tracks of the CD and, in the end, stops. Sometimes it manages to identify the disc and start playing, but there may be frequent failures while the music is playing.
In case of such failures, first of all, you should check the serviceability 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. To do 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. Once the carriage moves into place and the platter drive motor rotor begins to rotate, the lens on the laser head should move up and down using an electromagnet. At the same time, if you look at the lens from a certain angle, you will notice a thin red laser beam. Completion of all the above processes indicates that the laser head is working properly. To eliminate problems with reading CDs, sometimes it is enough to wipe the surface of the lens with a soft cloth. This should be done very carefully so as not to damage the lens or tear it off the electromagnet mount. If there is no improvement or it is insignificant, it is most likely that not only the lens is dirty, but also prism 2 located under the lens (see Fig. 1). To clean the prism surface, it is necessary to remove the laser head from the device.
The lens and electromagnet are fixed on metal plate 1. They can be covered with a small plastic cap with latches. This cap must be removed, then unscrew the fastening screws 6, which press the metal plate to the base 5. By carefully lifting the plate, you can see a small hole under the lens. Wrap a small piece of cotton wool around a match and dip it in alcohol, wipe the surface of the prism. Then very carefully put the metal plate with the lens in place and screw it in with screws 6. After this, close the head electromagnet with a protective plastic cap and put the head in place. In most cases, the laser head cleaned in this way 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 tape recorder may occur. When you press the play button, the motor shaft starts to rotate, but stops after a few seconds. In such cases, rewinding may work.
This malfunction occurs mainly due to weakening of the belt tension between the engine pulleys and the drive shaft of the tape recorder. In most CVLs with auto-reverse, used in music centers, instead of a four-track head, a two-track head with a rotation mechanism is installed. Rotation of the head when reversing the direction of movement of the tape in the tape recorder requires a certain force at the moment of switching. When the belt tension weakens (due to aging of the rubber), the head rotation mechanism gets stuck 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, which sometimes occurs in digitally controlled devices that have been in operation for several years, manifests itself in the cessation of volume control by the regulator located on the device itself; In this case, volume adjustment from the remote control is valid. Such failures arise because in such music centers, instead of the usual variable resistors - volume controls, special sensors are installed - valcoders, the rotation of which closes the corresponding contacts, and the processor, depending on the direction of rotation of the shaft, changes the gain in the path. When these contacts become dirty or oxidized, malfunctions occur and normal sound volume control is disrupted.
Troubleshooting involves cleaning the encoder 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 a rotary encoder is soldered - the volume control. After dismantling, it is disassembled by straightening the metal frame-mount, then the internal contact tracks are washed with alcohol, they are cleaned of oxide with an eraser (eraser) and washed again with alcohol. Before assembly, lubricate the contact tracks with a small amount of lubricant. A repaired encoder will usually work fine for several years.
Failure of a power amplifier in a music center often occurs due to careless handling - shorting the amplifier's output to a common wire or housing. Since in most music centers the power amplifiers are made on integrated circuits, repairs may consist of simply replacing the microcircuit with a working one. However, there may be cases when it is difficult to find a similar microcircuit, especially where there are no stores selling imported radio components, and it is not possible to stock up on a wide range of elements in advance. There are also cases when, as a result of the combustion of the microcircuit, the inscription on it has disappeared and it is not possible to determine the type of microcircuit. If the circuit diagram for the device cannot be found, you can repair the device by using a TDA1557 or TDA1552 chip instead of a burnt one. These microcircuits are distinguished by the fact 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 chips - 2x22 W - corresponds to most mid-priced music centers.
Before installing a TDA1557 or TDA1552 microcircuit instead of a faulty one, first of all, check that the supply voltage in the music center matches the supply voltage of the microcircuit itself. As a rule, it does not exceed 15... 17 V, which is quite suitable. In the absence of a music center circuit, use an oscilloscope to find which pins of the microcircuit receive the input signal. Having turned on playback from a CD or cassette and set the volume control to maximum, touch the oscilloscope probe one by one to the contact pads at the location of the old microcircuit. Having found the signal circuits, you should evaluate the signal amplitude and, depending on this, use the TDA1557 microcircuit (the sensitivity of its amplifiers is high - 50... 100 mV) or TDA1552 (with signal amplitudes up to 250...500 mV). Please note that input signals to the microcircuit must be supplied through isolation capacitors located on the board. The circuit diagram for connecting the microcircuits is shown in Fig. 2. As can be seen from the diagram, only the power and input signal of both channels are supplied to the TDA1557 (TDA1552), and the load is connected directly to the output pins. The microcircuit is mounted on a heat sink installed on the board; wires are soldered to its terminals, which connect them to the board. Various attachments used with the old microcircuit do not need to be removed.
At input 11 of the microcircuit (see Fig. 2), you need to apply the Stand-By signal, which controlled the operation of the old microcircuit. It can be found as follows. By connecting a voltmeter or an oscilloscope to the contact pads in turn at the location of the old microcircuit, turn the music center on and off with the button on the front panel and find a place where, when the center is turned off, the voltage is close to zero, and when it is on, it is close to the supply voltage. If this signal cannot be found, then, as a last resort, pin 11 (Fig. 2) can simply be connected to the positive power bus of the microcircuit.
I had the opportunity to change output amplifiers in JVC and Panasonic music centers (one of the MATSUSHITA brands). The results of such a replacement of the output microcircuit turned out to be good. If the output power turns out to be slightly too high, then it can be reduced to the required level by cutting the tracks on the music center board in the input signal circuit before the separating capacitors and soldering in the resistive dividers shown in Fig. 3. By selecting resistors R1 and R3, we achieve output power reproduced by the speakers of the music center without distortion. It is unacceptable to exceed the output power more than before, as this can lead to failure of the dynamic heads or the power supply of the music center. If you use surface mount resistors as 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 radios; it allows you to significantly improve the quality indicators and output power of an average quality car radio.
And finally, another malfunction, which also occurs quite often, is a defect in the network transformer. If you have a diagram and know the 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.
This malfunction must be eliminated, starting with checking the serviceability of the power cord and fuses. If fuses are included in the secondary circuits and the mains voltage comes directly to the primary winding of the transformer, but 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 on top of the primary winding, but other options for its location are possible. If this fuse is missing or it turns out to be intact, but there is a break in the primary winding, then the transformer will have to be changed or rewinded accordingly. Rewinding the primary winding in a transformer from a music center is sometimes difficult. Firstly, the winding is covered with varnish, and the wire is thin, and it turns out to be impossible to count the turns while gradually winding it up (the wire often breaks). Secondly, even knowing the number of turns, it is often not possible to lay them as tightly when winding as was done at the factory, and as a result, the wound winding does not fit into the transformer frame or in the magnetic circuit window. Therefore, it is easier to find out what the secondary voltages should be and wind another transformer or select a ready-made one - fortunately, there is usually enough space inside the music center.
It is best to start clarifying the voltage values in the secondary winding circuits by searching for a diagram or any voltage labels on the printed circuit board. If this is not the case, then you can try to determine the voltage using one of the microcircuits. The best way is to look at the power amplifier microcircuit (find out the rated voltage of its supply from a reference book). As noted above, in most cases this voltage is within 14... 17 V. Knowing it, we can accordingly assume what the voltage on the transformer winding should be. If, for example, the nominal 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 approximately 1.4 times (at low load), there should be 12-13 V on the transformer winding, respectively. 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, this is not difficult to do even with varnished windings. 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
UН = wН U2/w2
where UН and U2 are the voltage of the unknown and known windings, respectively; wН and w2 are the number of turns of the corresponding windings.
When winding the windings of a new transformer, the diameter of the wires 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 malfunctions discussed in the article may require an individual approach, and the methods for eliminating them may differ from those described by the author, but I would like to hope that the recommendations outlined here will help craftsmen, especially beginners, when repairing stereos and other household audio equipment.
I. KOROTKOV, Bucha village, Kyiv region, Ukraine
Instructions
Find out the cause of the malfunction of the music center. The most frequent and obvious breakdowns can be associated with a violation of its parameters or the absence of sound as such. Check the sound speakers (speakers) with a tester for voltage.
Use a working speaker from another device to make sure that the reason for the loss of sound does not lie in the center itself. If, after connecting working speakers, there is still no sound, there is a problem with the music device itself.
Disassemble the body of the music center. To do this, unscrew all the mounting screws with a Phillips screwdriver and remove the rear protective cover of the device. This will get you to the main board and you can inspect it.
Inspect the connection between the input connector and the copper traces on the main board of the music center. Use a soldering iron to restore the soldering in those places where it is damaged. To do this, it is better to use low-temperature solders that melt at 100 degrees, or generally conductive glue, so as not to damage the integrity of small parts of the board.
Play the music center in all possible modes (radio, cassettes, MP3 player) and check for irregularities. If in all modes the sound is reproduced with the same noise, then the problem is in the output amplification path. Damage to the power amplifier. To fix it, replace the damaged amplifier chip with a working one.
After troubleshooting, carefully inspect the main board again. It may have poorly soldered areas, swollen capacitors, darkened traces and other defects that may soon make themselves felt. Replace all “suspicious” parts. In this way, you will prevent another breakdown of your music center and extend the life of your equipment.
Sources:
- Music center FIRSTaustria TCD
- Music center repair
Sometimes the music center does not have an MP3 function, but the pocket player does. But the player, unlike a music center, is not capable of sounding loudly. To correct this drawback, you need to connect the player and the center to each other.
Instructions
First, check your stereo for RCA input jacks on the front panel, labeled AUX or PHONO. Don't confuse them with headphone or microphone jacks - they are not only made to a different standard, but are also designed for a different purpose.
If you do not find such sockets, then carefully, so as not to tear off any cables, turn the music center with the back wall towards you. You will probably find such nests there. Do not confuse them with sockets for other purposes, which can also be made according to the RCA standard.
Now take the unnecessary headphones. Cut off the sound emitters from them. Purchase two RCA type plugs. Strip the wires that went to the sound emitter. One of the pairs consists of a clear (or yellow) and a red (or orange) wire, and the other has a blue or green wire instead of a red or orange wire. Connect all colorless or yellow wires to the ring contacts of the plugs, and the red (orange) and blue (green) wires to the pins.
Connect the cable to the player and music center. On the last one, select the mode called AUX or PHONO. If it has several inputs, they may be designated AUX1, AUX2 and the like. When searching for an input, set both the player and the center to a low volume. In the future, set the volume on the player so that the center preamplifier is not overloaded, and then make adjustments from the center side.
To prevent the player's battery from draining, connect the device to a special power supply that emulates a USB port. You can also use a powered USB hub that is connected to the unit but not to the computer. Remember that if the player is powered not by a battery, but by a battery, charging the latter in any way is not allowed. Using a music center together with a player does not exclude the possibility of switching it to other modes if necessary.
Some novice radio amateurs are not eager to take on the repair of rather complex electronic devices, such as CD or MP3 players, computers or stereo systems. In fact, most of the malfunctions of the same music center are quite easy to fix, having minimal knowledge in the field of electronics and a little experience in handling equipment.
You will need
- - soldering iron;
- - solder;
- - flux;
- - headphones;
- - working speaker.
Instructions
Determine what type of problem you need to fix. It is quite difficult to cover all the problems with music centers. Most often you have to deal with the absence of sound or a violation of its parameters (timbre, signal amplification, frequency characteristics).
Start looking for the cause of the sound problem by checking the speakers. To check, connect another column (speaker) with a resistance of 4-8 Ohms. You can use a working speaker from an old TV or tape recorder. Typically, the load resistance value is indicated on the back wall of the device case next to the corresponding connector.
If, after connecting a working speaker, sound appears or its quality is restored, the fault should be looked for in the speakers. Otherwise, you will have to look at the internal circuits of the music center.
If you hear wheezing during playback, and the sound appears and disappears, look for the cause of the malfunction in a broken connection between the input connector and the contact copper tracks on the main board of the playing device. Restore the soldering in places where it is broken.
Check the operation of the music center in all modes: receiver, cassette deck, MP3 player mode. If the sound disturbance occurs in all three cases, the failure is most likely associated with the output amplification path, namely the audio power amplifier. To finally make sure of this, connect your headphones to the “Phone” jack, remembering to turn down the volume. The absence of sound in this case indicates the failure of the specified amplifier. Replace the amplifier chip with a working one.
Even if the described actions eliminated the problem, inspect the printed circuit board to identify poorly soldered areas, “swelling” of electrolytic capacitors, darkened traces and other defective installation elements. Replace identified faulty elements. Such prevention will prevent larger malfunctions during further operation of the music center.
Firmware programs are periodically released separately for each hardware model. A software update is necessary in cases where malfunctions occur or the previous firmware version becomes outdated.
The music center is designed to read media and listen to radio broadcasts. The receiver module is easy to detect after disassembly by the presence of a thin metal (foil) screen. Inside the steel box: high-frequency amplifier, local oscillator, mixer, and 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 stage is a stereo low-frequency amplifier, through which sound passes through the music center to the speakers. Isolation through transistor switches controlled by the position of the regulator on the front panel of the household appliance. Repairing a music center with your own hands is not always possible; it’s interesting to see what’s inside.
The structure of a typical millennium music center
Let's try to see how to fix a Samsung music center yourself. We came across a useful technical description and will read it. We'll leave the repair of Sony music centers for next time. The radio receivers in music centers are wide-wave, and the creators did not bother too much with the circuit; they made two paths:
- For amplitude modulation at medium and low frequencies.
- For frequency modulation on VHF.
We avoid describing the subtleties of dividing the ranges, just remember: small FM antennas receive a frequency modulated signal. Paths can be implemented on one chip (like KA2295Q) or separately. Before the detector, both paths are incompatible due to the specifics of signal processing. You can amplify a weak one and mix it with the local oscillator frequency, but don’t interfere with subtlety: each stage of the Earth still has a limited frequency band. We repeat, up to and including the detector, the paths go separately. The advantage of the integrated solution is described by its high specialization; automatic frequency adjustment eliminates worries about uncertain signal reception by the music center.
Many people cannot imagine a device that refuses to play cassettes. There are usually two decks, they work alternately for playback, and are controlled mechanically. At the circuit level, the amplifier switches to the desired head. The tape drive mechanism has one motor, pulls the tape, the reels are slightly spring-loaded. The recording and playback paths are separate, you can write:
- cassette tape;
- cassette receiver;
- laser disc reader-cassette.
Today a chip for decrypting MP3 and other formats is being added. The flow enters the low frequency amplifier. It is not difficult to notice the microcircuit; the case is placed under a good-quality heatsink of respectable size. Here the lion's share of the energy consumed by the music center is lost; other stages work with a low-amplitude signal.
Simultaneous playback from a tape recorder and a laser disc is not provided. Would make sense when mixing home original recordings. The microphone works in all modes. Allows you to record karaoke on tape and sing along with artists on the radio.
Read-write preamplifiers are assembled using one chip, for example, K22291. The film erase current is generated by a transistor generator. It is clear that the frequency differs greatly from the sound one. We must not forget about a software or microcircuit-implemented equalizer. Simpler than a steamed turnip, a cascade that places emphasis on a selected part of the spectrum of the recording being played. It is customary to listen to rock while showering your neighbors with bass; a low-pass filter makes a contribution.
The operation of the laser disc drive is controlled by a controller responsible for focusing and tracking tracks. Samsung uses the KA9220 microcircuit, which controls the motors through the KA9258 drive device and amplifiers. There are two drive motors, one rotates the disk, the second positions the head. The KA9220 controller directs the work and pre-deciphers the head signal. Further sound processing is carried out by the KS9282 signal processor, the waves are corrected and interpolated. To eliminate high-frequency interference, filtering is carried out using the KA9270 microcircuit.
The music center must have a system controller. A microcircuit that controls the operating modes of the equipment. Some Samsung music centers use MICOM LC866216 for these purposes. For interactivity, the controller is supplemented with an indication panel and keys. Through the interface, the user controls the music center. The infrared radiation receiver of the control panel is located on the front panel. It is worth noting: the central controller analyzes the position of the volume knob and generates signals for adjusting the low-frequency amplifier (a microcircuit on a large radiator). The control bus is digital, so you don’t need to look for a transistor-based volume control.
Switching power supply. Contains input signal filters, a high-frequency pulse generator that controls a transistor switch, output filters, and sometimes rectifiers using Schottky diodes. The voltages are stabilizing. The transformer and fuses are placed on a separate board. The device refuses to turn on - it’s logical to start repairing a music center with your own hands from here. There are several supply voltages, be sure to ring the secondary windings.
Schematic diagram of a music center
Let's consider the 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). The following is a typical circuit: mixer with local oscillator, detector. The restructuring of the circuits is carried out by varicaps using the voltage of the automatic frequency control microcircuit of the LM7000 music center. For smoothing, the signal is filtered before being sent to the varicaps. The receiver local oscillator frequency is controlled by the LM7000 chip. Signal selection is carried out mainly in an intermediate frequency amplifier. Before it, the frequency jumps, here it takes a fixed value (10.7 MHz). Therefore, piezoceramic filters are easier to set up.
The KA2295Q microcircuit, as mentioned above, is represented by a combination of an amplitude and frequency detector and selects the useful signal from the carrier. This includes a path of medium and long waves. Including local oscillators, mixers, amplifiers. The first stage is equipped with automatic gain control. For correct operation of the frequency detector of the music center, a phase-shifting oscillatory circuit is required. Automatic gain control works based on the mixer signal. It is necessary that the intermediate frequency amplifier and frequency converter do not enter cutoff mode.
From the frequency modulation detector, the signal is supplied to the pilot tone stereo decoder through a filter. Information about the presence of a stereo signal is provided to the central controller. You can force select the mode using the regulator. The central controller of the music center receives information about the state of the signal and controls the formation of sound. Channel balancing occurs using a variable resistor. The filtered signal enters the TDA 7318 chip, where the main low-frequency amplifier stage of the music center begins.
In the MF and LW bands, loop antennas with transformer coupling are used. The device of the music center includes transistors for switching channels across bands. The heterodynes are switched as needed by electronic switches. The adjustment is carried out by varicaps, the adjustment is made using AFC signals. The high-frequency amplifier is broadband and is not switched in the music center. The intermediate frequency in the MW and LW bands is 450 kHz (typical value). The detected signal, without passing through the pilot-tone circuit, is immediately fed to the filters and to the output amplifier of the receiver. As for the MF and LW, the circuit communicates with the central controller of the music center about the fact of frequency capture, which helps the “brain” to be aware of events.
It remains to add that there are two channels, it’s just that the sound is different on FM frequencies, and the same on LW and MW. Which is what is called, in fact, stereo and mono. When reading cassettes and discs, the situation is similar; you can artificially bring separate playback to continuous playback. The differences between the channels of the music center are leveled out.
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 music center, we will return to this later. The master must know in advance what will break. Repairing music centers yourself will seem like child's play.
Always look for original factory diagrams and descriptions before digging into the electronic insides of household appliances. Microchip drawings are open to free access by copyright holders. The purpose of the chips is described on the manufacturers' websites.
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