Constant voltage amplifier without output special fault repair circuit diagram

Filter 18.432M

The boot check found that one of the two 10000μF/100V power supply filter capacitors exploded, so the burst capacitor was removed and the electrolyte on the board was carefully wiped off. Then check the power to see no signs of short circuit in the tube, and finally put a new 10000μF/100V filter capacitor and 15A fuse inside the machine, the power test machine is all normal, after a few days of use, the relay can sometimes pick up when booting. Sometimes it can't be sucked in, accompanied by an alarm sound. It has also been found that there are the following rules: After the power is turned off for a long time, the first time the relay is turned on, the relay can basically pick up. When the power is turned off shortly after the shutdown, the relay can sometimes pick up and sometimes not pick up. According to the above phenomenon, it is estimated that the DC potential of the output terminal to the ground is not zero when the fault occurs, so the power supply voltage at the time of the fault is measured, and the power supply voltage is found to be asymmetric. The voltage of the newly replaced filter capacitor side is 118V, and the other capacitor is two. The terminal voltage is only 68V (normally, the voltage across the two capacitors is 91V).

Then found that the negative power indicator is off much slower than the positive power indicator, so it is suspected that the electrolyte is not wiped clean on the board or the performance of individual transistors is poor, after spending a lot of time to eliminate the above possibilities I only turned my attention to an inconspicuous thing - the bleeder resistance. After the measurement, the 5.6kΩ/5W open circuit on the negative power supply side was found, and the fault was completely eliminated after the replacement.

Analysis of the cause of the fault: The cause of the fault is that the balanced resistor is open, causing the power supply on the front panel of the power amplifier board to be unbalanced, causing the output of the power amplifier to deviate from the balance point. The interference protection circuit of the audio signal does not function well, resulting in One of the capacitors burst due to long-term operation at 120V. After the capacitor is replaced, the balance can be established due to the randomness of the pre-stage establishing balance. Sometimes the balance cannot be established. If the preamplifier is balanced at this time, the amplifier stage is balanced by the pre-stage control and the balance is established. Since the quiescent current of the power amplifier stage is large, the influence of the balance resistor can be neglected at this time.

According to the above analysis, I feel that this machine is suitable for capacitors with a withstand voltage of 150V.

As shown in the picture, Hangzhou HENTR brand constant pressure amplifier has no output special fault repair circuit diagram