Yamaha CT-7000 Service Manual page 9

Operation
1. Touching the tuning knob with your finger passes
the electric potential in the human body to the TS
terminal, and it is amplified by Trl
rectified by Dl and D2
2. This potential is added to the base of Tr3, switch­
ing it on and grounding the AFC terminal (i.e., cancel­
ing the AFC effect).
TRANSIENT NOISE CANCELATION CIRCUIT
This circuit serves to cancel the noise and distortion
caused by turning the Power
and Tr2, then
diodes for (+) potentiaL
switch on and off.
0�
CONNECT
THE I>
TERMINAL
OF Fig5
10/25
Fig. 4
STATION INDICATION SIGNAL
!1
AFC
3. At the same time, this potential is fed to the base
of Tr4, so that that transistor comes on and grounds
Tr5 with 15k.Q.
4. When the station display signal is fed to
terminal, Tr5 comes on and switches Tr6 on. This lights
the AFC/Station lamp. At this time, if operation (3)
above is added, Tr5 output voltage
output impedance rises, so that the AFC/Station lamp
dims to show that the AFC is off.
Operation
1. When the Power switch is turned on
When the power is switched on, potential at point®
is equal to E, and rises to +12V according t() a time
constant decided by Cl Rl. When this +12V is added
to the base of Trl this transistor switches on nd shuts
so that the difference i n voltage obtained
Tr2 off,
by Cl Rl appears as it is at terminal 0. This switches
Tr7 (previous diagram) on, and the same condition
continues until the voltage at point@ reaches -+11.5V ,
thus cancelling unwanted signals at the
is switched on.
2. When the Power switch is turned off
When the power is switched off voltage at p oi nt
changes from 12V to
rectified to couple voltage by D3D4, and neg<t ive load
potential is obtained at point @. This switch es Trl
off .and Tr2 comes on, so that E potential is
at the
collector of Tr2 and
change is available at terminal 0, providing
effect at the instant the power is switched CJ�ff.
D2 removes the ripple in the negative voltagE .a t Point
@
which means it cancels the operation o1 1:his cir­
cuit, which works via ripples whe n the powl.- switch
is turned on.
12V60mA
AFC/STATION
LAMP
Fig. 3
the I
drops and Tr6
tirre power
This cl"l ang e is
E potential.
pre sent
the negati ve �ote ntial
muting
1
CT-7000
1
1V
7