As we all know, we use the power amplifier in our daily life. After a long time, various problems may occur. So, how should the power amplifier be solved? Interlaced across the mountain, although not all people can solve it, but knowing some relevant knowledge will make you easy to solve. The following describes three common faults and maintenance methods for the amplifier.
First, the whole machine does not work The whole machine does not work. The fault is that there is no display of the amplifier after power-on, each function key is invalid, and there is no sound, like when it is not powered.
The power circuit should be checked first during maintenance. Use a multimeter to measure the DC resistance at both ends of the power plug (the power switch should be turned on). Normally, there should be hundreds of ohms. If the measured resistance is much smaller and the power transformer is severely heated, it indicates that the primary circuit of the power transformer has a partial short circuit; if the measured resistance is infinite, check whether the fuse is blown, whether the primary winding of the transformer is open, the power cord and the plug There is no disconnection between. Some machines add a temperature protection device, and a current fuse is connected in the primary circuit of the power transformer (usually installed inside the power transformer, the insulation paper outside the transformer can be removed), and it will also make the power transformer primary after damage. The circuit is open.
If the resistance of both ends of the power plug is normal, you can measure whether the output voltage of the power supply circuit is normal. For amplifiers that use a system-controlled microprocessor or logic control circuit, it is important to check that the supply voltage (usually +5V) of the control circuit is normal. If there is no +5V voltage, the input voltage of the three-terminal regulator IC 7805 should be measured. If the input voltage is not normal, the rectifier and filter circuits should be checked. If the voltage of the 7805 input terminal is normal, and the output terminal has no voltage of 10V or the voltage is low, you can disconnect the load and see if the +5V voltage can return to normal. If the +5V voltage is normal, the fault is in the load circuit; if the +5V voltage is still abnormal, the fault is in the 7805 itself. If the +5V supply voltage of the system control circuit is normal, check whether the clock and reset signal of the microprocessor are normal, whether the key control and display drive circuit are damaged.
Second, the noise of large noise amplifiers are hum, pop, induced noise and white noise.
During maintenance, you should first determine whether the noise is from the previous stage or from the latter stage. The signal connection plugs of the front and rear stages can be removed. If the noise is significantly smaller, the fault is in the front stage circuit; otherwise, the fault is in the latter stage circuit. AC sound refers to the low-pitched, monotonous and stable 100Hz AC hum, which is mainly caused by poor filtering of the power supply. It should be checked whether the power rectifier, filter and voltage regulator components are damaged. The decoupling capacitors at the power supply terminals of the front and rear stage amplifier circuits are either weakly soldered or failed, and a low frequency oscillation noise similar to the hum is also generated.
Inductive noise is a complex and harsh humming component, mainly due to poor switching of the front-end circuit, poor grounding of the potentiometer, or poor shielding of the signal wiring. The popping sound refers to the intermittent "劈啪" and "咔咔" sounds. In the pre-stage circuit, it should be checked whether the signal input plug and the socket, the transfer switch, the potentiometer, etc. are in poor contact, and the coupling capacitor has no solder joint or leakage. The post-amplifier circuit should check whether the relay contacts are oxidized, whether the input coupling capacitor is leaking or has poor contact. In addition, the soft input breakdown of the differential input tube or constant current tube in the latter stage circuit also produces "咔咔" noise similar to electric spark. White noise refers to the random continuous “sand†sound, which is usually caused by the poor performance of the input stage transistor, FET or op amp integrated circuit in the front and rear stage amplifying circuits. The component of the specification is replaced by a test.
Third, the volume is light, the so-called sound and light fault, refers to the audio signal in the process of amplification and transmission, due to a certain amplification level of the amplification amount is changed or attenuated in a certain link, so that the amplifier's gain decreases or the output power becomes smaller. When overhauling, first check if the signal source and speaker are normal, and you can use the replacement method to check. Then check the various types of transfer switches and control potentiometers to see if the volume can get bigger.
If all the above parts are normal, it should be judged whether the fault is in the pre-stage or in the post-stage circuit. For a certain channel sound, the signal output of the front stage circuit can be input to the subsequent stage circuit of the other channel. If the sound size of the speaker is unchanged, the fault is in the latter stage circuit; otherwise, the fault is in the previous stage. Circuit. The sound caused by the post-amplifier circuit is light, mainly due to two reasons: insufficient output power and insufficient gain. It is possible to determine which cause is caused by appropriately increasing the input signal (for example, adding the signal output from the recorder to the speaker directly to the input of the rear stage power amplifier circuit, changing the volume of the recorder, and observing the change in the output of the power amplifier).
If the input signal is increased, the output sound is large enough, indicating that the output power of the power amplifier is sufficient, but the gain is reduced. It should be checked whether the contact resistance of the relay contact increases, the input coupling capacitance decreases, and the resistance of the isolation resistor increases. Negative feedback capacitor capacity becomes smaller or open circuit, negative feedback resistor resistance increases or opens. If the input signal is increased, the output sound will be distorted, and the volume will not increase significantly, indicating that the output power of the post-amplifier is insufficient. First check if the positive and negative supply voltage of the amplifier is low (if only one channel is light) , it is not necessary to check the power supply), whether the performance of the power tube or integrated circuit is deteriorated, and whether the resistance of the emitter resistor is increased or not. The sound caused by the switch and potentiometer in the pre-stage circuit is light and easy to find by visual inspection, which can be cleaned or replaced. If it is suspected that a signal coupling capacitor fails, it can be tested in parallel with the same value capacitor; the performance of the amplifier tube or op amp integrated circuit is poor, and it can also be checked by the substitution method. In addition, there is a problem with the negative feedback component, which also causes the circuit gain to drop.
In the actual operation of the console, if you do not have a certain amount of relevant knowledge, the operation is quite difficult, and at the same time, the sound quality effect is often unsatisfactory. Therefore, in order to improve the output of the mixer, it is important to learn and understand the knowledge of the demodulation station.
1, the sound is harsh: cause: high frequency energy is too strong; solution: attenuation 6KHz;
2, the sound is irritating: cause: high frequency is not compliant; solution: attenuation 8K-1OKHz;
3, the sound hair: Reason: ultra-high frequency energy is too strong; solution: attenuation 12K-16KHz;
4, the microphone is dry, singing tired: the reason: the microphone IF energy is not enough; solution: increase the 800Hz frequency band;
5, bass hard: reason: the upper limit of the subwoofer energy is too strong; solution: attenuation 125-160Hz;
6, bass dispersion: Cause: low frequency lower limit energy is too large; solution: increase the subwoofer lower limit frequency.
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