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qqHservice manual download site
qqHservice manual download site
The second step is to access big power tube, keeping dummy loads, step-down power supply, monitor the midpoint. In other words, put on a last stage of power transistor Q212~Q219, and follow the method from 50V gradually boost continues to electrify a trial. When necessary, the whole quiescent current, neutral-point voltage to be adjusted accordingly. If the midpoint voltage wrong, should focus on late-stage power amplifier tube and peripheral circuits. Until the midpoint voltage stability, power FETs and thermal radiation so far.qqHservice manual download site
qqHservice manual download site
The third step is to remove the dummy load, access cheap speakers and signal source, normal power listening. Specifically, respectively, in Figure 1 c, d and e, d indirectly trying to listen into the low-end speakers. At this point, even if the circuit fails, but only damaged cheaper low-end speakers. Power listening for half an hour, the midpoint voltage should remain stable, power amplifier tube temperature should be normal (not burn). Conditional indicators by testing and tuning.qqHservice manual download site
If c, d room listening to audio, in between e and d trying to listen to the silent, is the speaker protection circuit malfunction, repair and protection circuit should be checked.qqHservice manual download site
Above Yamaha EMX2300 amplifier is used for servicing the above method first step power test machine, find the midpoint between the c and d voltage too high and drive pipe Q210 and Q211 heating smoke. Stop the machine immediately, and repeated testing of circuit elements, contrast, metamorphic components showed no damage. Later control schematic diagram check circuit, found on the base of the differential input stage Q202 bias resistor R210 is not directly connected to ground, but through the plug connected to the tuning platform lines again formed a circuit with the power end. While in the power on test machine, for convenience, not connected to the mixer, resulting in differential amplifier Q202 lose bias voltage,qqHservice manual download site
qqHservice manual download site
Differential Amplifiers out of balance, by direct coupling, midpoint of the resulting output (c, d), high voltage, burnt complementary power pipe Q212~Q219. R210 grounding wire directly to a connected with the amplifier ground b, and may leave virtual connection and connected to the mixer outlet weld after weld, then follow the first step power test machine, neutral-point voltage is restored the 0V, adjust the midpoint voltage of input voltage is stable.
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