Kenwood TK-230 Service Manual page 29

TK-230/230(SC)
CIRCUIT DESCRIPTION
1.RX Audio Switching ON/OFF
If no selective signaling option is employed, the
receive audio muting is done by controlling the power
supply for the AF power amplifier !C in the PA sub-unit
of the TX-RX unit and ICQ and O5 (audio signal line) in
the control unit.
When the selective signaling (CTCSS or Digitally Con-
trolled Squelch) is enabled, audio muting is performed
by monitoring the detector (DET) output signal.
Audio muting is performed by controlling the power
supply for the audio amplifier, the same as for the noise
squelch.
For driving the speaker with the BEEP alarm during PA:
ON, T.0.T. and LOCK OUT, PA: ON and SP: ON are set
to high. The BEEP signal from the MPU passes through
a LPF before being amplified and applied to the speaker.
During DTMF output, part of the DTMF signal from
the signaling unit is routed to the audio amplifier. Only
PA: ON and SP: ON are set to high and DTMF side tone
is applied to the speaker.
All three signal output levels are adjustable by using
the volume control and the level compensation of each
signal is done with a summing resistor.
When switched to EXT, the SP: ON signal is set to
low and the INT SP signal is turned off. (Figure 9]
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