Xianke VCD machine maintenance circuit diagram

Example 1? Fault phenomenon: AL-P678K model, after inserting the disc, the screen displays "NO DISC" and the disc is not read.

Analysis and maintenance: Based on the phenomenon analysis, it is initially estimated that the focusing servo circuit of the laser component is faulty. Open the upper cover of the machine, turn on the power, and observe. It is found that the disc does not run after being put into the warehouse. At this time, there is no resistance when gently turning the disc by hand, and the operation is normal. After ejecting the disc, I observed that the up and down focusing and tracking movements of the laser head were normal, but found that the spindle motor was not running. It was suspected that the spindle motor drive circuit was defective or there was a problem with the spindle motor. Remove the movement component and measure the resistance of the spindle motor to be normal. Based on this, it is suspected that the circuit of the laser component is defective. After careful observation, a red laser beam is emitted from the laser head. The laser head of this machine is Philips 1204 type, which is integrated with the integrated circuit. After replacing the original laser component with a new one and testing the machine, the disc reading and playback were normal.

Example 2? Fault phenomenon: AL-P678K model, press the box ejection button on the panel, the tray does not come out of the box, but the "OPEN/CLOSE" characters are displayed normally on the screen.

Analysis and maintenance: After analysis, it is initially estimated that the out-of-box detection circuit is defective. After opening the upper cover of the machine, turn on the power, press the box ejection button on the panel, and observe that the box ejection drive motor is operating normally. Pull the pallet outward by hand, and the pallet can extend. When you press the close button again, the pallet can only enter about two-thirds of the way. When you push it inward by hand, the pallet enters normally. After careful observation, it was found that the belt was loose and slipping. After replacing the belt with the same size and testing the machine, the pallet enters and exits the warehouse normally, and the fault is eliminated.

Example 3? Fault phenomenon: AL-P628B model cannot read the disk.

Analysis and maintenance: Disc recognition is one of the functions that a V CD player must have. The machine has a disk but cannot read the disk, indicating that the fault is in the RF detection and A PC circuit. The RF detection and APC circuit of the machine is shown in the attached figure. As can be seen from the figure, when the power is turned on, the U1052 pin outputs the serial command (SILD) to light up the laser diode and sends it to the U104{25} pin. The U1042 pin outputs a high level and sends it to the U1037 pin. The U103{16} pin outputs Approximately 4V operating voltage is supplied to the APC circuit to light up the laser diode. At this time, if there is no CD in the machine, the photosensitive diode will have no output, the U10310 pin will have no RF signal output, and the U1042 pin will output a low level, causing the U103{16} pin to output 0V, and the LD will stop emitting light. At the same time, because U1057 pin is high level, its {16} pin outputs a diskless signal. When a disc is installed in the machine, the photodiode receives the reflected light, and U103 processes the reflected light into an RF signal, which is output from pin 10 → C501 coupling → T501 amplification → C502 coupling → D501 limiting → T502 amplification → D502 detection → C503 integration → R508→T503 turns on, outputs low level→U1057→U1052 outputs disk serial command→U104{25}→U1042 outputs high level→U1037→U103{16} outputs 4V working voltage→APC circuit→LD continues to emit light, At the same time, U105 controls each servo circuit to start working, and the laser head reads the information on the disk and enters the playback state.

The MD in the APC circuit detects the luminous intensity of the LD at any time, and converts the intensity of the laser into the equivalent resistance, so that the b-pole voltage of T3 changes with the intensity of the laser. When the LD luminescence is enhanced → MD equivalent resistance decreases → T3’s b-electrode voltage decreases → C-electrode voltage increases → T2’s b-electrode voltage increases → E-electrode voltage increases → T1 output current decreases → LD luminous intensity weakens. VR is used to set the b-pole voltage of T3, reduce the resistance value of VR, and increase the b-pole voltage of T3, which can increase the output current of T1 and increase the luminous power of LD. The resistance value of VR is set according to the rated luminous power of LD and cannot be adjusted to a lower value at will, otherwise the service life of the LD will be shortened.

It can be seen from the analysis that when the LD ages or the objective lens and 45° reflector in the laser head are blocked by dust, the laser intensity will drop significantly, and the amplitude of the RF signal output by the U10310 pin will also drop. Even after amplification by T501 and T502, D502 The DC voltage generated by the detection and C503 integration cannot turn on T503, so the U1057 pin does not have a low level, so it is processed without a disk. Open the casing, clean the dust on the objective lens and 45° reflector of the laser head, and then try the machine again, but the fault remains. After careful observation, we found that the laser head has up and down focusing movements, but does not emit light. Use a multimeter to measure the voltage at pins U1037 and {16} and it is normal, indicating that the fault is in the APC circuit or the laser diode LD itself. Tried replacing the LD and the fault remained unchanged. After replacing the A PC circuit board, the fault was eliminated.

Example 4? Fault phenomenon: Model AL-P638, the fluorescent screen does not light up, but other parts work normally. After pressing the function key, control characters are displayed on the screen.

Analysis and maintenance: Other functions of the whole machine are normal, and corresponding control characters are displayed on the TV screen after pressing the function keys, indicating that the fault is in the fluorescent display and its power supply. The display screen adopts pulse driving mode, and the display content is provided by the CPU to pins 8 (CLK), 9 (STB), and 6 (DAIN) of the driver block μPD16312 . G1~G6 of μPD16312 outputs 6 gate bit pulse control voltages to determine which blocks can emit light; A1~A20 of μD16312 outputs 20 anode segment pulse control voltages to determine which segments emit light. The gate and anode are usually at negative potential. Only when the pulses of the gate and anode are both at high levels , can the anode electrons bombard the anode and emit light. To display on the display screen, the following signals must be present: (1) input pulses from pins 8, 9, and 6 of μPD16312; (2) 3.15V filament voltage and -25V voltage; (3) gate control pulse; (4) ) anode control pulse. When measuring the gate control pulse with an oscilloscope and a multimeter, it was found to be constant -25V, and other signals were normal. Since the anode control pulse was normal, it was obvious that the fault was in the gate control part inside μPD16312, and it was determined that the integrated block was damaged. After replacement, the fault was eliminated.

Example 5? Fault phenomenon: AL-P698K model, the boot image is normal, but the sound is abnormal. When using the RF output terminal, the whole machine is silent. When using the AV terminal, there is a small accompanying sound, but the image is normal.

Analysis and maintenance: Based on the above phenomena and combined with maintenance experience, the fault is likely to be in the decompression board or the audio reverberation circuit. Based on the principle of first easy and then difficult, first take out the audio signal from the audio output end of the decompression board and send it to the power amplifier for amplification. The result is that the sound is normal, indicating that there is no problem with the decompression board, so the fault must be in the audio reverberation circuit.

The audio reverberation circuit of this machine is composed of three NE4558 op amp blocks including U305, U307, and U308 and their peripheral components. According to the conventional steps, after powering on the machine, first test the positive and negative power supplies of these op amp blocks. It was found that the negative power supply (-10V) power supply is normal, but the positive power supply power supply is abnormal (the actual measurement is +0.8V, the normal power supply should be +10V). ), it is concluded that the fault is caused by this. So I checked along the line, and finally found that the electrolytic capacitor of C368 (47μF/16V) connected to the b pole of the +10V power control tube Q311 (9014) had serious leakage. After replacing it with a new one, the fault was eliminated.