Kenwood KRC-767D Service Manual page 10

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CIRCUIT DESCRIPTION
3-3. Music signal detection time Tc and the mute circuit
To prevent malfunction against any noise in the gap between
tunes, a music signal detection function is incorporated into
this unit. With this function, the plunger drive pulse is output
only when the detected signal is longer than the music signal
detection time Tc. Therefore, the pulse is not output when the
detected signal is short (noise is present). The length of Tc is
determined by the value of the capacitor Cc which is con-
nected to pin 6.
Also, when pin 6 is grounded, the mute circuit is engaged to
stop the between-tunes gap detection operation. In this case,
the input resistance of the input pin (pin 3) is lowered (to ap-
prox. 1 kohm) to prevent deterioration of the crosstalk bet-
ween channels of the L/R both-channel input system.
Cin O.022yF
Cin 0.022 pF
3-4. Output circuit
The output circuit is an open collector design, and is suitable
for the situation in which the plunger is turned ON during
searching operation. The maximum allowable driving signal is
one having a pulse width Tw of 200 ms, duty cycle of 30 %
and an output current lo of 100 mA.
For the mute function, the output signal is turned OFF forcibly
and the signal level becomes high.
Since the IC might be damaged due to the counter elec-
tromotive force generated in the solenoid of the plunger, a
discharging diode should be inserted in parallel to the
solenoid.
[] Plunger
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