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Bel AV-368 power amplifier, the left and right channels have no output

Time：2015-05-25 15:03:08 Source：Network Author：Unknown Clicks：1605

01, 02 working States conform to the above analysis of the interaction between the circuit voltage: outputs midpoint voltage ↓ → ↓ → b voltage of Q2 Q2 Q1 current ↑ ↓ →. And can therefore differential amplifier formed by Q1, Q2, working conditions were normal. -43.9V Q3 c measuring voltage. For -3.4V,Q4 c-e voltage voltage for -43.3V. E voltage -3.5V,R9, R10 junction voltage is -3.4V. According to this measurement, analysis of R10 ends there is a voltage drop, the Q4 current through R9 no voltage drop at both ends, concluded that no current through Q3. But if the Q3 e current, Rll ends there should be no voltage drop measured 03 c voltage for -43.9V.

Rll has current can be determined through, and without the current Q3, R9 (R9 ends no pressure drop).

According to the illustrated circuit, analyzes the current path through the Rll only: 1. through Q3, b → c R9 circulation; 2. b, c is circulation of Q6; 3. C3 (leakage) in circulation. Try to disconnect the Q3 c. "Fault" no changes; split Xia Q6 measuring its resistance pressure normal, rat its c, and b very no reverse leakage phenomenon; split Xia C3 (100pF porcelain tablets capacitor), with multimeter RxlOk block measurement no exception, but at amplifier has recovery normal work, proved "fault" Department C3 leakage due to, with same resistance pressure of capacitor replaced C3 Hou try machine, not only voice output recovery normal, found volume runaway "fault" also automatically excluded.

Check the circuit structure, found outside the amplifier outputs in addition to the speaker protection circuit. Diverged along the path to the volume control circuits.

Estimated midpoint of the output end of the original circuits may be designed with the boot moments before the zero potentiometer is not set up properly.

Use the error voltage, or use the speaker protection circuit time delay function volume control potentiometer to zero function. To ensure the relay when the suction volume is in minimum position, avoid the volume of machinery and equipment and the hearing cast too much impact.

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