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9. At the same time, the noise of the AF signal is detected by
squelch circuit in IC1 and the output is sent from pin 19 of IC1.
CPU Board:
When receiving continuously, IC9 (C3V) is turned ON and IC11 and IC13 are set to RX operation.
When receiving periodically, ON/OFF of IC9 (C3V) is controlled. The followings are under the
condition that C3V is ON in RX mode:
1. The AF signal output from pin 15 of IC1 is supplied to pin 23 of
IC13 (CTCSS) through pin 3 of CN4, then amplified and passed
through the band-pass filter to be output from pin 7.
2. IC13 checks the exsistence of CTCSS signal and its frequency (60
~ 250 Hz) in AF signal. If the check result matches to the
programmed conditions, it turns off the mute and AF signal is
output from pin 7 of IC13.
3. The AF signal output from IC13 is led to pin 23 of IC11 and
amplified to descramble passing through the filter in the scramble
mode. (TR325)
4. Furthermore, the signal is returned by the expander to be output
from pin 17, then it is amplified at the amplifiers of pin 18 and pin
19 to be output.
5. The voice signal is input to the pin 4 of the power amplifier of
IC12 for the main speaker, and differential outputs from pin 5 and
pin 8 to drive the speaker.
6. The signal for the sub-speaker is amplified one more stage in
IC11 and output from pin 21. It is supplied to pin 4 of the power
amplifier (IC10) for sub-speaker. Differential outputs from pin 5
and pin 8 drive-Differential is output from pin 5 and pin 8 to drive
the sub-speaker.
7. 2 amplifiers are turned ON/OFF by the control terminals (pin 1
(SD0, SD1)) respectively. (They don't work at the same time.)
8. The output terminal of main speaker is connected to the speaker
through the external output terminal (CN2).
9. When the external speaker (headset/speaker microphone) is
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