Working principle, as shown in the figure: mainly divided into three parts. These are the power supply circuit, the satellite box amplifier circuit, and the subwoofer circuit.
1. Power circuit (the bottom part of the drawing): 220V mains enters the transformer primary after the fuse (F) and switch S. The secondary output of the transformer is dual 12V AC, and the dual 12V is sent to the bridge rectifier composed of VD1 Circuit circuit, after bridge rectification and C14, C15 (3300UF / 25V) filtering, the output no-load voltage is about plus or minus 16V (root number 2 times 12V), that is, A + is positive 16V, A- is negative 16V. Positive and negative 16V provide power for the three power amplifier chips TDA2030 and UTC2030. After the voltage drop of R21 and R22 is applied to the other channel, the positive and negative 12V output from B + and B- will provide the power supply voltage for bass preamplifier and low-pass filter IC4.
In this drawing, the preamplified power supply does not use the 78/7912 three-terminal voltage regulator circuit. Mill lovers may also consider adding LM7812 / 7912 to provide more stable work for the front when replacing two 3300UF capacitors Voltage.
Second, the left and right channel amplifier circuit (satellite box power amplifier circuit), because the principle of the left and right channels is completely consistent. Here I will only use the left channel of the drawings as an example to make an introduction. As shown in the figure: RIN is the signal input terminal, and enters the volume potentiometer through the coupling capacitor C23. ), After adjusting the volume, the signal enters the treble boosting circuit composed of R1 / C3. This circuit can boost a certain amount of high-frequency signal to make the sound clearer. After that, the signal enters the left channel power amplifier through the coupling capacitor C1, pin 1 of UTC2030, after power amplification, it is output by the fourth pin of 2030, and pushes the satellite box to sound. In the figure, R7 is the feedback resistor, and R7 / R9 is the magnification factor that determines the 2030 chip. Therefore, by adjusting the resistance of R7, the magnification can be adjusted. R11 / C7 is the speaker compensation network.
3. Subwoofer circuit. From the left and right channels through the two 10K resistors R5 and R6 to the C11 coupling capacitor, the signal then enters IC4, pin 3 of the model JRC4558, and IC4A in the figure is the subwoofer preamplifier. R201T sets this amplifier's magnification to about 6 times. (R17 / R18), after pre-amplification, to ensure that the driving voltage is large enough to obtain a sufficiently large volume. Pin 1 of 4558 is the front output, and enters the low-pass filter composed of IC4B, C9, C10, and R20 after R19. The role of the low-pass filter is to cut off low-frequency signals below 200 Hz, and R20 and C10 determine the cutoff frequency. (The specific cut-off frequency setting of each manufacturer is slightly different). After the output of IC4B ---- C19, connected to the input terminal of the volume potentiometer, after adjusting the volume of the subwoofer, the output of the slide terminal of the potentiometer enters the subwoofer amplifier circuit IC3; TDA2030A, the principle of this circuit is consistent with the satellite box amplifier . Pin 4 is the output terminal, which pushes the woofer to sound.
The above is the basic working principle of R201T. By the way, there is an error in the above figure: that is, the 1-pin input terminal of TDA2030A should be marked as "+" which is the non-inverting input terminal. Pins 1 and 2 on the drawing are reversed.
Note: Rambler R1900TII, 1800TII. Light Cavalry V23SE, Hivi M200, M20W, M20L T120. The chip used in LM1875T. Its working principle is consistent with TDA2030A in this article
2.1 Speaker repair method:
Master the basic principles of the circuit, and repairs will be more efficient. In fact, overhauling the audio system is like paying attention to "watching, smelling, asking, and cutting" like a doctor looking at a patient.
Things to do before overhauling: don't rush to start when the audio encounters a malfunction. First of all, ask the user about the use: before and after the fault, what is abnormal with the sound, such as whether there is a "kaka" noise, whether you smell an odor, whether you see the sound of the smoke, etc., so you can quickly understand the sound status. When you encounter problems such as silent sound or mono sound, don't rush to judge the sound itself; instead, first eliminate the problem of the signal source and the connecting cable. For example, check if the computer is muted, is the system volume adjusted to the minimum position? ? ? ? Is the balance control in the middle? ? ? ? After confirming that there is no problem with the sound card or DVD / CD signal, you should also check the output audio cable. Sometimes, the contact of the cable is not enough to cause mono or noise. Also. Also check the connection clips of the satellite box for looseness. (Sometimes you can swap the two satellite boxes to determine whether the satellite box and the power amplifier circuit are good or bad); make sure that the signal source and the connection cable are no problem, and you have decided to dismantle your speakers for maintenance when the fault has not been eliminated.
The following uses R201T as an example to introduce several common troubleshooting methods for speakers:
1. There is no response when starting up, neither the satellite box nor the subwoofer sound. (At this time, there is no response when adjusting the two volume potentiometers). This failure can basically be regarded as a power failure. (Because the probability of three power amplifier chips being damaged at the same time is very low). If the insurance tube of the multimedia audio is installed outside. We can unscrew the fuse cover, take out the fuse, and observe: if the fuse has melted, do not rush to replace it with a new fuse. We can observe the situation of insurance damage: if the fuse is only broken in the middle or both ends, there is no obvious trace of burning black. It can be estimated that the insurance was accidentally damaged. (Because of the high mains voltage, etc.) At this time, the replacement of the insurance tube with the same specification can generally be excluded. (If the fuse is installed in the main box, you need to remove the cover to remove the fuse).
If the wall of the fuse is burnt black, it is estimated that the transformer is burned (or short-circuited between turns). In addition, short-circuiting of components in the rectifier or filter circuit will also cause this phenomenon. At this time, we can observe the transformer for odor and see if there are any signs of burning. At the same time, you can use a multimeter to check whether the secondary output voltage. If the output of the transformer is normal, it is necessary to check whether the four rectifiers are short-circuited, whether the capacitors are short-circuited, and so on. Until the short-circuited component is detected.
2. Mono. For example, if the left channel is silent, we can remove the left channel satellite box and access the right channel satellite box. If the satellite box sounds at this time, you can confirm that the cause of the failure is that the satellite speaker of the left channel is faulty or burned. If the right satellite box is connected, the fault remains, indicating that the speaker is good, but the left channel amplifier circuit is damaged. . (You can also swap the left and right channels of the audio input line behind the R201T to determine the working state of the 2.1 speaker). So, how to repair the left channel power amplifier circuit? ? ? ? ? Let's look at the drawings. In the picture, I have marked A, B, C, D, E, and several "key points". IC2 is a left-channel amplifier circuit, we can use a simple and effective "signal injection method" (also called signal interference method), specifically using medical metal tweezers or other small screwdrivers (hands touching the metal part), Directly touch point B in the figure. That is, pin 1 of the power amplifier chip. At this time, the loudspeaker should have a large "click" interference sound. If not, then it can basically be judged that the power amplifier chip has OVER. We just use the same type of chip replacement. UTC2030 can be directly replaced with UTC2030, TDA2030, TDA2030A. At the same time, it should also be noted that the R10 and C6 of the inverting input terminal of the TDA2030A are disconnected or damaged, which may cause sound blocking or even silence. In addition, there is a broken circuit board copper foil at point A --- B, which will also cause the left channel to be silent. The premise of the above maintenance method is: when the working voltage of IC2 is normal. (That is, pin 3 is negative 16V, and pin 5 is about 16V).
3. No sound from the subwoofer. We can directly use the R * 1 block of the multimeter to measure the woofer. The speaker should have a small "kaka" sound, otherwise the speaker will be damaged. When the horn is normal, we still use the signal injection method. In order to quickly find the fault point, we generally interfere from the "back" to the "front". That is, the first stage of the power amplifier is injected with the signal, and if there is no fault, the signal is injected into the previous stage.
As shown in the figure: the interference signal is injected at point F, and the woofer should have a “popping soundâ€; otherwise, the TDA2030 power amplifier circuit must be repaired. If the popping sound is normal, but the subwoofer does not work, we can check the volume potentiometer of the bass. After eliminating the problem of the potentiometer, the problem cannot be solved, then check IC4. IC4 has two functions, one is pre-amplification and the other is low-pass filtering. If the power supply of IC4 is abnormal or damaged, it will cause the silent failure of the subwoofer. (Note, pin 8 of IC4 is positive 12V and pin 4 is negative 12V). Before conducting the above inspection, we have to visually observe whether the circuit board is broken and whether the components are obviously burned. This way you can avoid detours.
Continued, TDA2030A is a relatively easy to damage device, except for the signal injection method. We can also use the following method to quickly determine whether 2030 is good or bad ---- We first check whether the power supply of the chip is normal, that is, 5 feet are positive 16V, and 3 feet are negative 16V. In the absence of signal input, the other three pins should be zero voltage. If the DC voltage output of pin 4 (power amplifier output) is measured, (even reaching about 16V), it is determined that the chip has been damaged. In particular, pay attention to: pin 3 of TDA2030A (LM1875) is connected to the heat dissipation contact surface. If there is no pad insulation between the heat dissipation surface and the heat dissipation plate, please remember when repairing: the heat dissipation plate should not touch the ground wire or power line Otherwise, the chip may be damaged.
4. When adjusting the potentiometer, the speaker has the noise of Kaka. This fault can be cleaned with WD-40. Reference: http: //? U = bbs & id = 20040216225824sb If the wear is severe, replace it with a potentiometer of the same specification.
5. There is "howling" sound or loud noise in the speaker. When a rectifier diode of the rectifier circuit breaks down or the filter capacitor fails. It may cause this malfunction. How to judge whether the filter capacitor is invalid? ? ? ? We can detect A +, A- voltage. The normal voltage should be around 15V. When it is detected that a certain group of voltage is only about 10V, it is estimated that the corresponding filter capacitor has failed. For example, if A + only has 10V, then C14 has failed and lost its filtering effect. Replace it with a capacitor of the same specification.
Sixth, the subwoofer has a loud "Weng Weng" sound when it is not playing music. Even if the input signal cable is unplugged, Weng Weng is still very large and cannot be eliminated. This phenomenon is generally caused by a malfunction of the bass channel circuit, and the most likely cause is damage to the TDA2030A chip. Cause the TDA2030 pin 4 to output a DC voltage, so that the speaker emits a dull "Weng" sound, and only need to replace the power amplifier chip to solve the problem.
See the three pictures in reply 5, we can quickly identify the pin sequence of NE5532 and TDA2030A. Color picture one: the pin in the middle is NE5532 (JRC4558) pin 1. The bottom figure is the identification of each pin of the dual op amp. At a glance.
NE5532 (JRC4558) pins: 1 is the output of the op amp, 2 is the inverting input, and pin 3 is the input. Pin 5 is the non-inverting input of the other op amp, pin 6 is the inverting input, pin 7 is the output. Pin 4 is the negative voltage , 8-pin positive voltage.
The actual picture in the middle is 2.1. The TDA2030A power amplifier chip commonly used in speakers. This chip is a dual in-line package. Count from left to right: feet 2 and 4 are close to the heat sink. The front row is followed by feet 1, 3, and 5. (LM1875 pins are exactly the same).
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