Talk about the inspection and judgment of common faults of power amplifier

by:Gisen     2020-01-05
Amplifier, short for power amplifier, commonly known as 'amplifier '. It is the most basic device in the sound system. Its task is to amplify the weak electrical signal from the signal source to drive the Speaker to make a sound. The following is a way to check and judge the six common fault phenomena of the power amplifier. (1) Fault phenomenon: silent, all indicators on the panel are not lit. Check: Does the current limiting protector at the back of the amplifier pop up in a protected state? If it pops up, reset it. If the power indicator is on but no output. Can you open the cover to check if the fuse on the motherboard is blown? Replace the fuse of the same specification without damage to other devices. (2)Fault phenomenon: silent. On the panel, the power indicator, the wave indicator, and the protection indicator are on. Check: sometimes you can smell the burnt smell, which is caused by the device burning out. There are four main causes: a, power amplifier motherboard high power tube, Fet breakdown. In this case, the fuse on the motherboard has also been blown and must be returned to the factory for repair in this case. Because the bias current needs to be readjusted after replacing the transistor, more devices will be damaged if the user replaces it himself. B. The power filter capacitor and thermistor on the Power board overflow and burst due to the aging of the service time. After replacing the same specification device, the machine can work normally. C. Rectifier bridge damaged. The damage of this type of device often occurs at the same time as the breakdown of the high power tube. The analysis is caused by the instantaneous breakdown of the device by the large current after the short circuit. Replace the rectifier bridge of the same specification, however, pay attention to the polarity of the four lead-out ends when replacing. D short circuit of transformer is extremely rare. The fuse and the current limiting protector will not appear until the above short circuit occurs in the power amplifier. If it is the quality problem of the transformer itself, the probability of occurrence is generally within one thousandth. Only one case has been encountered in the past few years. (3) After starting up, when there is no signal, the signal indicator light has been lit for inspection: First check the power board. If a filtering electrolytic capacitor on the Power board is damaged, the rectified positive and negative voltages will be different. The same specification capacitor should be replaced. If the Power board is good, check the main interface board again. There is a set of positive and negative 15V on the main interface board, and the voltage is provided to the front amplification circuit and the excitation amplification stage. When the 15V voltage regulator on the motherboard is damaged, the voltage imbalance will occur. As a result, the circuit is not working properly. (4) The sound is distorted, and the wave-cutting indicator on the panel is lit. Check: As mentioned earlier, the power supply part of the power amplifier is in a secondary power supply mode. When the high and low power supply voltages in the circuit are not converted with the signal strength, the large signal operation will cause wave distortion. In this case, the dynamic negative feedback circuit of the previous stage or the sampling circuit is damaged and needs to be returned to the factory for repair. (5) Fault phenomenon: the cooling fan rotates slowly or stops. Check: whether the cooling fan of the power amplifier works normally plays a vital role in ensuring the work of the machine. Therefore, the power amplifier should not continue to be used when the fan speed is slow or not, otherwise it will enter the shutdown protection state because the temperature inside the machine is too high. During the inspection, it is first judged whether it is an AC 220V power supply fan or a DC 24V power supply fan. For the AC power supply fan, the key point to check is whether the 564/630V Safety capacitor of the control speed is open. If the fan performance is normal, the fault can be eliminated after replacing the new capacitor. The DC power supply fan is relatively simple. If the 24V voltage is normal, the fan is basically bad. There are still many machines that return to repair because the dust is too blocked and the fan is not working properly. It is recommended to remove dust at the site first. If it still does not work, return to the factory for repair. (6) When the machine has no output or the output volume is large and small, check: when the machine is used for a long time, dust and the use environment will cause oxidation of the volume adjustment potentiometer and lead to poor contact. The basis of the judgment is that there is mechanical noise when adjusting the volume, and the same type of potentiometer can be replaced. Some machines returned for repair are caused by loose terminal or output socket, and this part of the device should also be inspected at site. The common faults and maintenance methods of power amplifiers are described above. In short, once the failure of the power amplifier occurs, it should be analyzed and judged by experienced professionals. In particular, the maintenance of the main interface board since the high power tube of the power amplifier is working in parallel, all the power tubes on the motherboard with short circuit phenomenon should be removed for screening during measurement. Since the high-power triodes are screened and paired before production. The bias current is also accurately debugged during production. Therefore, it is not recommended that customers replace the device at will. In order to avoid greater damage caused by incorrect parameters. In addition, the replacement of the voltage regulator diode must also pay attention not only to the same voltage regulator value, but also to the same power of the voltage regulator. The ordinary 1W Voltage regulator cannot be used instead of 1. 5W pressure stabilizing tube. In our maintenance records, there are cases in which the customer repairs all the power tubes in the machine and burns out the electrolytic capacitors and the rectifier Bridge. This has brought great difficulties to our maintenance, and has also increased the maintenance costs of customers for machines that have passed the warranty period.
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