Product Alias |
Yamaha power amplifier |
Region oriented |
|
brand |
other |
Number of rear (surround) speakers |
4 |
Number of center speakers |
4 |
Front dimension |
6 |
Format of host playing disc |
CD |
With DVD or not |
With DVD player |
Video connection mode |
Mixed Video |
Product category |
Power amplifier |
USB |
yes |
FM frequency modulation |
support |
Bluetooth function |
support |
Microphone |
support |
Shanghai Yamaha Power Amplifier After sales Service Center
Yamaha power amplifier after-sales service hotline: 4001140858
Yamaha EMX230 power amplifier maintenance:
The front stage of high fidelity OCL and OTL power amplifier circuits mostly adopts differential amplification input, and the final stage adopts complementary high-power transistor output, with direct coupling between the front and rear stages. It has the advantages of stable operation, good frequency characteristics and low distortion, so it has been widely used in recent years and in household power amplifier circuits. However, due to the use of multi tube direct coupling, once a component deteriorates or is damaged, the working point of the whole circuit will be changed, ranging from low sound and distortion to extensive damage to components and even burning of the speaker system. The change of voltage at one point will cause the change of voltage at multiple points, which also makes it difficult to judge and repair faults. When communicating with peers, it was also found that when repairing such power amplifiers, if the fault is not eliminated, the new components are often damaged again when the power is turned on for test run, resulting in economic losses. Therefore, the author tried out a safety maintenance method in the maintenance practice, and introduced it to everyone in the form of examples in order to communicate with peers.
Example 1 When a colleague overhauled a Nissan Yamaha EMX2300 power amplifier and mixer combination machine, he found that 16 high-power butt tubes and 4 push tubes of the two power amplifiers were all broken down, and the speakers in the two speakers were all burned out. After replacing all the damaged parts according to the specifications and without connecting the front mixer, power on and test the machine. After only a few minutes, smoke can be seen in the machine. After shutdown and inspection, 12 new high-power butt tubes were damaged, and the speakers in the two speakers were burned again, with a loss of more than 2000 yuan. He didn't dare to repair it again, so he turned to the author for help. Having learned from the past, after careful consideration, the author adopted a safe and sound method for maintenance and troubleshooting.
The specific maintenance steps are as follows:
(1) Make clear the working principle and component parameters of the circuit by referring to the physical object and the schematic diagram (see figure).
(2) Use resistance measurement method to measure all components in the circuit once, and compare the measurement results of left and right circuits to find out the damaged components.
In order to improve the in circuit measurement, a digital multimeter is used to measure the resistance. Because the internal resistance of the digital multimeter is large and the current supplied to the circuit under test is small, the diode and triode PN junction cannot be connected, which is equivalent to an open circuit and can reduce the impact on resistance measurement. Use a pointer multimeter to measure diodes and triodes. When measuring the forward resistance of the PN junction, use R × 1 gear, which can not only provide a large forward current to the PN junction, check its forward characteristics, but also reduce the impact of other components on the test. Under normal circumstances, when measuring the forward resistance of the PN junction with a 1.5V battery powered resistance block, the pointer should deflect to the midpoint of the resistance range scale line (about 0 Ω 1/2 away). If the displayed resistance is large, it indicates that the forward characteristic of the PN junction is poor. When measuring the reverse resistance, use R × 100 or R × 1k gear, and the display resistance should be slightly less than the parallel resistance between the two test points. When measuring capacitors (especially electrolytic capacitors), a pointer multimeter is also used, and the corresponding range is selected according to the size of the capacity. It can not only measure the resistance of the capacitor in the circuit, but also estimate the capacity of the capacitor according to the swing of the pointer.
After in circuit measurement by the above method, 12 high-power output tubes of the combination machine were broken down, 5 emitter resistances were burnt out, two push tubes leaked electricity, and the loudspeaker protection circuit failed. After all the above components are replaced with new ones and the loudspeaker protection circuit is repaired, the key power on test run phase is started.
(3) The three-step safe power on test method is adopted for power on test. In order not to damage the loudspeaker and high-power tube, the loudspeaker system is not connected before the test run, and a 20~50 Ω/20~50W wire wound resistor is connected between the push-pull output terminal and the ground (that is, between point C and point D in Figure 1) to make a false load. Secondly, disconnect any two electrodes of the last stage high-power tube or do not install high-power tubes Q212 ～ Q219 in advance. Keep the push tubes Q210 and Q211 for complementary push pull output (if there is no emitter resistance between the emitter and the midpoint of the push tube, two resistors of 100~270 Ω and above 0.5W should be temporarily installed and removed after commissioning). Then connect a voltage regulator in series at the 220 V input end of the power supply of the power amplifier, supply power to the power amplifier from 50 V, and monitor the midpoint voltage of the output terminal (the voltage between point C and point D). This voltage shall be 0V ± 0.5V for OCL circuit and half of the power supply voltage for OTL circuit. If the neutral point voltage does not meet the normal value, stop the machine for inspection immediately. At this time, due to the low power supply, the components will not be damaged generally. If the midpoint voltage is normal, gradually increase the power supply voltage. While monitoring the midpoint voltage, observe whether there are discoloration and smoking elements, and feel the temperature of the push tube with your hand. If the mains power rises to the normal value, the output terminal voltage remains unchanged after half an hour of power on, and there is no temperature rise or deterioration or discoloration of components and parts in the driving tube, it indicates that the safe power on test run is over, and the next step can be carried out. The second step is to connect the high-power tube, maintain the false load, step down the power supply, and monitor the midpoint. In other words, install the last stage high-power tubes Q212~Q219, and continue to power on and test the machine according to the method of gradually increasing the voltage from 50V. If necessary, the static current and neutral point voltage of the whole machine shall be adjusted accordingly. If the midpoint voltage is abnormal, check the final power amplifier tube and peripheral circuit. Until the midpoint voltage is stable and the power amplifier tube is not heated. The third step is to remove the false load, connect the low-grade loudspeaker and signal source, and test the normal power supply. Specifically, connect low-grade speakers between C and D and between E and D in Figure 1 for audition. At this time, even if the circuit fails, it will only damage the low-end speaker at a lower price. The midpoint voltage should be stable and the temperature rise of the power amplifier tube should be normal after half an hour of power on listening. The indicators can be tested and adjusted if conditions permit.
If there is sound in C and D, and no sound in E and D, the speaker protection circuit is faulty. Check and repair the corresponding protection circuit.
When the machine is powered on and tested with the above method, if it is found that the voltage between the midpoint C and D is too high, and the push tubes Q210 and Q211 are heated and smoke, the machine should be stopped immediately. Repeated detection and comparison of circuit elements show that no damaged or deteriorated elements are found. Later, the circuit was carefully checked against the schematic diagram, and it was found that the bias current resistance R210 on the base of the differential input stage Q202 was not directly connected to the ground wire, but was connected to the ground wire of the console through the plug socket, and then formed a loop with the ground terminal of the power supply. During the power on test run, the differential amplifier stage Q202 was not connected to the mixer for convenience, which led to the loss of bias voltage of the differential amplifier stage Q202 and the imbalance of the differential amplifier. Through direct coupling, the voltage at the midpoint (between C and D) of the output terminal was high, and the complementary high-power transistors Q212~Q219 were burned. Connect R210 ground wire A directly to power amplifier ground wire B, repair the socket connected to the mixer that may be falsely soldered and falsely connected, and then test the machine according to the steps. The midpoint voltage recovers to 0V, and the midpoint voltage of the regulated input terminal voltage is stable. Connect 16 power amplifiers for the second step of power on for half an hour, and there is no abnormal phenomenon. After that, remove the false load, connect the low-grade loudspeaker and mixer between C, D and E, D, and input the CD signal to listen for several hours. The midpoint voltage remains unchanged, and the power amplifier tube has no obvious temperature rise. business as usual. This machine has been used by users for two years, and no similar failure has occurred again.
Hotline for repair: 4001140858
Key words: Shanghai Yamaha power amplifier after-sales service telephone Yamaha power amplifier after-sales customer service telephone
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