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2-9 Linear AFT
The AFT-S signal which is outputted
from pin 44 of ICI 01 is supplied to the AFT pin on the
tuner through the AFT defeat circuit consisting
of Q704, Q705, Q706 and Q707. The AIT
defeat circuit is driven by the AFT defeat signal output from pin 10 of the CPU, which is AFT
ON (L) or AFT OFF (H).
During normal operation,
the AFT-S signal is supplied to AFT pin on the tuner through Q706
and Q705.
During tuning or channel changing,
Q704 is turned on by the "High" signal from pin 10 of the
CPU. When Q704 is turned on, Q705, Q706 and Q707 are turned off. As a result, the AFT-S
signal is prevented
from reaching the tuner, and the DC voltage from divider R754 and R753
.
is supplied to the AFT pin on the tuner instead.
Once the tuning or channel operation
is completed,
the AFT-S signal is supplied to the AFT
pin on the tuner again.
For this reason it is called Linear AFT.
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CPU
10
AFT
Defeat
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