Hi-fi system is designed to read media, listen to the radio broadcast. Receiver module easily detected after disassembly by the presence of thin metal (foil) screen. Inside a steel box: high-frequency amplifier, oscillator, mixer, and other stages. Repair of electronic circuits are not subject to, the individual parts are more expensive than the device as a whole. The musical centers used superheterodyne circuit with a frequency conversion. The final stage put the stereo low frequency through which the music center of the speakers sound passes. Isolation through transistor switches controlled by the position controller in the front panel of the household appliance. Repair of the music center with their own hands is not always possible, it is interesting to see what's inside.
The device is a typical musical center of the time of the millennium
Let's try to see how to repair Samsung music center. Once in the hands of sensible technical description, will be read. Repair Sony Stereo leave for another time. Radios in music centers shirokovolnovye, the creators do not bother too much with the scheme did two paths:
- For amplitude modulation at medium and low frequencies.
- For VHF frequency modulation.
Avoiding paint fineness ranges division, just remember: small FM antennas are receiving the frequency modulated signal. Paths may be formed on a single chip (such as KA2295Q) separately. And the detector both paths are not compatible due to the specificity of the signal processing. To strengthen the weak mix with the local oscillator frequency can not prevent fineness: each stage of the earth still has a limited bandwidth. Again, up to and including the detector paths are separate. The advantage of integrated solutions described high specialization, automatic frequency tuning eliminates the concern over insecure receiving a stereo signal.
Many people do not represent the device refuses to play the cassette. December usually two, are working to reproduce alternately controlled mechanically. At the level of the circuit is switched to the correct amplifier head. A tape drive motor, pulls the tape reel almost biased. Paths separate recording playback, you can write:
- the tape cassette;
- Cassette receiver;
- reader laser disc cassette.
Today, the chip decryption added MP3 and others. Feed enters the low-frequency amplifier. Chip is not difficult to notice, the body placed under Mighty radiator respectable size. There is lost the lion's share of the energy consumed stereo, other stages operate with a small amplitude signal.
Playing together with tape and laser disc is not provided. It would make sense in the mix of domestic copyright records. Microphone works in all modes. It allows you to write on the tape karaoke, sing on the radio artists.
Preamplifiers recording and reading are collected audio chip, for example K22291. film erasing current generator transistor is produced. Clearly, the frequency differs from the sound strongly. We must not forget the implemented software or a chip equalizer. A piece of cake, cascade, which emphasizes the selected portion of spectrum currently playing records. Rock decided to hear the neighbors showering bass, low-pass filter makes a contribution.
Operation of the drive laser disc fills the controller responsible for focusing, tracking tracks. Samsung applies KA9220 chip control the motor via the drive unit KA9258 and amplifiers. drive motors, two, one of the rotating disk, the second head is positioned. KA9220 controller fills the work head signal pre-decode. Further sound processing is KS9282 signal processor, the waves are corrected, interpolated. To eliminate high-frequency noise filtering is performed KA9270 chip.
The Music Center is certainly worth a system controller. Chip, responsible for equipment operation modes. Some Samsung music centers used for this purpose MICOM LC866216. For interactivity controller supplemented display panel and keys. Through the interface, the user controls the music center. On the front panel there is the infrared remote control receiver. It is worth noting: a central controller analyzes the position of the volume knob, tuning amplifier generates signals of low frequencies (chip on a large heatsink). digital control bus, so do not look for the volume control on the transistor.
The power supply switching. It contains input filters, high-frequency pulse generator, the key control transistor, the output filters, sometimes Schottky diode rectifiers. Voltage stabilized. Transformer fuses are submitted for a fee. The device refuses to be included - the Music Center repair their own hands it is logical to start from here. Multiple supply voltages, be sure to ring the secondary windings.
Schematic diagram of the music center
Consider the receiver. In case Samsung Stereo in the UHF band telescopic antenna signal arrives at the preselector (set of resonant circuits plus channel filtering high frequency amplifier). The following is a typical scheme mixer with a local oscillator, a detector. Restructuring loops held varactors using frequency locked loop circuit voltage LM7000 music center. To smooth the signal is filtered before being fed to the varicap. Receiver local oscillator frequency is controlled by the IC LM7000. The selection signal is produced mainly in the intermediate frequency amplifier. Frequency jumps to it, here takes a fixed value (10.7 MHz). Hence, piezoceramic filters configured simpler.
KA2295Q circuit, mentioned above, is represented by a combination of amplitude and frequency detector and extracts the desired signal from the carrier. This includes the path of the average wavelength. Including oscillators, mixers, amplifiers. The first stage is equipped with automatic gain control. For correct operation of the frequency detector music system needs a phase-shifting oscillation circuit. Automatic gain control on a signal mixer. It is necessary that the intermediate frequency amplifier, frequency converter has not reached the cut-off mode.
Since frequency modulation of the detector signal is fed through a filter stereo decoder pilot tone. Information about the presence of a stereo is issued to the central controller. You can choose to control by force. The central controller of musical center receives information about the state of the signal, controls the formation of the sound. Balancing channels occurs by means of the variable resistor. The filtered signal is fed to a chip TDA 7318, which begins stage main amplifier of low frequency musical center.
In the MW and LW range loop antennas are used with transformer coupling. music center apparatus includes switching transistors by band channels. Oscillators are switched as required with electronic keys. Tuning varactors being, adjustment is performed on the signals AFT. high-frequency amplifier is a broadband, not switched to the Music Center. Intermediate frequency in the MW and LW range of 450 kHz (typical value). The detected signal without passing scheme pilot tone is immediately fed filters, the output of the receiver amplifier. As for the MW and LW, the circuit communicates with the central controller of musical center frequency of the fact of capture, which helps to "brain" to keep abreast of events.
It remains to add, there are two channels, simply an FM sound different on LW and MW is the same. What is called, in fact, a stereo and mono. When reading tapes, discs similar situation can lead to artificially separate playback to Fused. The differences between the music center channels are offset.
It is important to understand the basic types of faults can be represented by an attentive study of the schemes. Not together an overview of the full and complete description of the music center, come back to this. The master must know in advance what will break. Self Repair of musical centers will seem like child's play.
Always look for original factory diagrams, descriptions, anticipating digging electronic guts of household appliances. Drawings chips open holders free access. Appointment chips painted sites of manufacturers.
