Core tips£ºIn the process of playing the disc, the sound of the Panasonic DVD A-300MU is suddenly disappeared, and all functions are out of play.
This machine plug in the power, standby, the red indicator light, press the "POWER" button, the red indicator light goes out, the green indicator light. Since then, sometimes can be a variety of operations and play, and sometimes a variety of functional keys and failure, can not play. In the process of the normal playback of the disc, and sometimes the picture, sound suddenly disappeared, all functions are failure. The failure of the emergence of the law, sometimes a power on the emergence, sometimes playing a night is no problem.
The circuit structure is complex, and there are some differences between VCD, SVCD, CVD player, with a lot of new circuit. To cause to overhaul the detours, first to Analysis > standby red indicator light and green indicating diode VD6506 lightening luminescence luminous process of diode VD6505, then again with fault phenomenon to narrow the range of possible fault.
First of all, the analysis of the standby red light emitting diode VD606.
The red indicator light emitting diode VD6506 is provided by the switching power supply circuit, first to analyze the working process of the switching power supply.
Switch power input circuit is mainly composed of L1002, Cl001, Ll001 - C1004, ZNR, VD1001, Cl011 and other components (see below the switching power supply of the left half part of the circuit). Where ZNR is a bidirectional diode over voltage protection element, which is used to prevent the high voltage from the power grid and the internal components of the machine. Ll001 and Cl001, l1002 and C1004 constitute two groups of different parameters of common mode filter, to obtain broadband inhibitory effect, used to filter out the grid voltage disturbance signal and prevent switching power supply pulse harmonic channeling into the power grid caused by pollution. The common mode filter has the characteristics of filtering the symmetrical disturbance of power supply. This is mainly due to the phase winding of two groups of coil inductance Ll001 or l1002, flowing through the current in the opposite direction, so that is can the interference signals in the core inductance formed magnetic fields cancel each other, so as to achieve the purpose of common mode rejection. In addition, Ll001 and L1002 of the two inductor coil winding is also with C1003, C1002 capacitor constitute two inverted "L" type LC filter, used to suppress the differential mode interference signal.
The ground wire of C1002 and C1003 capacitor is a cold plate ground (i.e., signal ground), in order to ensure that the filter and signal is in high frequency zero potential.
Power grid voltage poles LC filter, remove the interference in the power grid into the Cl011, VD1001 composition of the rectifier, filter circuit. > block (block winding ~ 3; tube added to, R1045 to unstable by the circuit will be AC220V voltage rectifier, filter is about 300V DC voltage, and then divided into three road to the switch power supply circuit: the first path R1046 VD1041 cathode second path switch transformation, Tl001 fifth added to thick film IC1011 foot IC internal strength rate of field effect transistor VT drain); the third path starting resistor r1021 r1022 step-down to thick film IC1011 fifth foot the foot about 8V starting voltage, which voltage is applied to the IC circuit, benchmark circuit, RL resistance to the oscillator pulse width modulation reference voltage, IC independent oscillation modulator, start to enter the work state. The pulse signal is amplified by the driving circuit and the gate of the VT resistance of the R4 in the IC. The Tl00l, the input rectifier, filter the DC voltage into AC voltage pulse. When the switch pipe cut-off VT, Tl0111 the primary side winding release magnetic storage energy Tl0112 time chopping preparing winding had induction voltage. The Tl011 7 ~ produced by the winding induction voltage by VD1021 rectifier, R1023 limit flow, C1021 filtering obtained fifth legs about 17V (DC) voltage is applied to the IC1011 (the voltage of the photoelectric coupler R1031 resistance is added to the photosensitive tube collector). Because the voltage is higher than the start voltage, the IC1011 and the current foot is mainly provided by the branch.
In this part of the circuit, the IC1011 and C2 within the R2 are outside the RC network to determine the oscillation frequency of the oscillator (which is set at about 200kHz).
VT1101, VT1102, VT1031, VD1101, Rll01, R1102 and other components of the error voltage sampling, detection and amplification transmission circuit.
Which VT1101 for error voltage detection and amplification, VT1102 tube and VD1101 regulator diode together constitute a benchmark voltage circuit.
The circuit is more special, increase the VT1102 tube, increase VTl102 tube to enable error detection circuit of reference voltage has strong load capacity, not due to changes in the current sampling circuits affect the stability of the voltage reference. The source of the error voltage and the power supply process.
1 source of error voltage
The error voltage is taken from the T1011 (16) ~ (15) ~ () VD1111 rectifier, the Cllll capacitor and the 6V inductor filter after the Lllll voltage output terminal. The voltage is applied to the base of the VT1101 tube by Rll01 and R1102 resistance.
The reference voltage of the circuit error from the switching transformer Tl01l (17) ~ (15) winding output pulse voltage -VD1131 rectifier, C1131 capacitor filter get 12V voltage, R1107 resistance, VD11001 voltage regulator tube 5.2v and added to the VT1102 tube base. After the shot with the device, the VT1101 emitter from the emitter to the error detection amplifier provides about 4.5V of the reference voltage.
2 power supply process
When the switching power supply for a certain reason causes the Tl011 transformer 2 time to the side voltage to rise to the Cllll the 6V voltage to the two ends of the high - > VT1101 tube pole voltage rises, its collector