Audio Pro B2-50, Руководство по обслуживанию

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1.2 Automatic ON/OFF
This circuit is powered via diodes D201, D202 and capacitor C201.
The power transformer and the Automatic ON/OFF circuit are powered
at all times when B2-50 is plugged in to a live outlet.
The other circuits in B2-50 are powered only when relay K101 is
actuated.
The audio signal on left channel is sensed by operational amplifier
Z201 (3, 2, 1) which acts as an amplifier with gain 5,000 at 500Hz.
The amplified voltage (point H) is limited to +7.0 V and -0,7 V
by zener diode D208.
Operational amplifier Z201 (6, 5, 7) and transistor V201 work
as a Schmitt trigger with ON level 7 V and OFF level 5 V. The
input (pin 5) senses the voltage from Z201 (3, 2, 1) after
rectification in D209 and capacitor C206.
Transistor V201 drives relay K101 and a red LED indicating "ON".
When toggle switch 5201 is in position "AUTO", relay K101 is
de-energized about 5 minutes after the audio signal on left
channel input disappears. The time delay is determined by C206
and R210. (During testing R210 may be shunted by 100 kohm, so
delay time is reduced).
When toggle switch 5201 is in position "ON" the sensing circuits
are bypassed, and relay K101 is energized as soon as B2-50 is
plugged in to a live outlet.
Temperature sensor TS3-85 senses the temperature of the Power
Amplifier heatsink. If this temperature becomes too high, the
resistance in TS3-85 drops to a low value, and relay K101 is de-
energized.