Yamaha CT-7000 Service Manual page 14

CT-7000
STEREO/MONO DRIVE AND STEREO INDICATOR
CIRCUIT
This circuit receives stereo
for stereo reception. When the
Operation
1. The composite signal is fed from the
and undergoes a high cut due to R1, C1 and C2. It is
added to the 19kHz 90
Tr1, R2 and C3. In this way the 19kHz pilot signal
°
and is amplified at Tr2
leads by 90
stereo broadcast reception, of course).
2. At the same time, the
put (7) enters via
operated by Tr4.
3. Using the phase difference between the pilot signal
and signal, Fig. 7 to see the potential at point� (i.e.,
the phase detector output, the following points be­
co me clear.
See chart 14.
The o peration to the detector when the
is phase locked is shown by the chart 15.
time the phase difference is zero, and maximu m posi­
tive o u t put is obtained.
4. T h e potential change is integrated by R3 and R4,
and when it is more than 0.25V, Tr5 goes on and Tr7
goes off, which switches
multiplex demodulator begins to operate and at the
same time the stereo indicator lamp lights, driven by
Tr9.
However, if the station display signal is not received
via 13, i.e., if the
is bel ow the muting level, the base of Tr8 will be
grounded through 02, keeping it off and keeping the
stereo indicator lamp from
demodulator will also fail to be activated.
12
FM
signals strong enough
PLL
circuit is phase
I terminal
1
°
phase shifter composed of
(only during
PLL D
circuit terminal out­
I
and the phase detector Tr3 is
2
PLL
At this
Tr8 on. In this way the
strength of the received signal
lighting. The multiplex
locked the demodulator operates and the stereo indi­
cator lamp
circuit
lights, which is this circuit's function.