Qisheng AV-713 amplifier connected AC220V power source, relay does not snap, analyzing and removing loudspeakers silent: relay not closing, first check the speaker protection circuit. This machine is the speaker protection circuit using a combination of discrete semiconductor devices and integrated circuits,d2bservice manual download site
Connect AC220V power source, a group of AC27V voltage transformer secondary output through the bleeder 3R1 (100 ω/2W) added to the rectifier diode 3D5 (1 N4002) of the cathode, 3D5 31V DC voltage of the cathode to be pulsating, after passing through the capacitor 4C2, 4C3 and 4R56 filters, obtain smooth DC voltage for the load. At of 4Q5 is as of, integrated block TC4001BP of 13 feet voltage for 0V, is II feet output high level, through 4R3, and 4R5 on 4C1 charging, after must of time Hou, 4C1 ends voltage is greater than 5.6V (DW of breakdown voltage), and DW breakdown, 4Q1 obtained b-e knot partial reset voltage and saturated guide pass, following electrical have electric, touch points sucking collection, will speakers access amplifier level output midpoint. Once the midpoint of the left or right channel amplifier output voltage is wrong, that is positive or negative voltage, this voltage via 4R1A, 4R1B and 4R2 hours after the pressure is tested gave 4Q3, 4Q4. 2 220RF/25V of electrolytic capacitors (item number 4C5) series, equivalent to 1 100 μ F/50V-polar capacitors. When you work in normal, 4C5 bypassed from the output audio signals sent by the midpoint, so as not to interfere with 4Q3, 4Q4 working conditions to prevent misoperation. Regardless of output midpoint voltage is are also is negative, 4Q3, and 4Q4 of set electrode voltage are will variable low, through 4R10, and 4D4 put 4Q5 base very voltage pulled to zero potential, 4Q5 saturated guide pass, set electrode output high voltage, gave TC4001BP of 13 feet, is TC4001BP of II feet output low level, 4Q1 as, following electrical release, thus achieved on speakers of protection.d2bservice manual download site
Dang due to a species causes caused power output tube launches very current had big Shi, as lost people signal had strong caused amplifier level overload, is through 2Q11, and 2Q12 launches very of current increases, its launches very negative feedback resistance 0.25 ω/5W Shang of pressure drop also will variable big, this voltage by 4R16, and 4C7 further smooth filtering, by 4R13 points pressure Hou plus to 4Q8 of b-e knot Shang, 4Q8 due to obtained high of partial reset voltage and saturated guide pass, through 4D6, and 4R12 put 4Q5 of base very voltage pulled low , The collector output high voltage 4Q5, sent to TC4001BP 13-feet, TC4001BP feet low output voltage of ②, 4Q1 closed relay disconnected. 1Q11, 1Q12 over-current protection process with 2Q11, 2Q12.

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