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3-3 Chroma Crystal Selection
The subcarrier oscillator crystals, X201 for 4.43 MHz and X202 for 3.58 MHz are used for both
colour demodulation
and sync. calibration circuits in IC101 (TDA8362).
When the colour system is AUTO, the output signals from pins 42 and 43 of IC701, CPU, are
"1-ligh",
Causing
Q221 and Q222 to be turned off, and both X201 and X202 are available for
oscillation.
IC101 identifies
the
colour
subcarrier
of the incoming
signal and selects the
correct crystal oscillator.
When the forced NTSC system is selected,
the CPU outputs
a "High" from pin 43 and a
"Low"
from
pin
42. Q221
is turned
on and Q222
is turned off. As a result, the oscillation of
X201 for 4.43 MHz is stopped by applying the DC voltage.
For other colour systems
using 4.43 MHz oscillation
in a forced mode, the CPU outputs a
"High" from pin 42 and a
"Low"
from pin 43 which turns Q221 off and Q222 on. The result is
that X202 is prevented from oscillating by the application of the DC voltage via Q222.
CPU
4:
4:
9
8V
R228
4.7k
R223
R224
47k
15k
Q222
*VV
R229
4.7k
V*V
...................................................................>
\
R222
4.7k
Q221
~4.43MH
Iclol
Video/chroma
34 3.53 MHZ
35 4.43 MHZ
System
Auto
PAUNTSC4.43
SECAM
NTSC
Pin 42
H
H
H
L
Pin43
H
L
L
H
Q221
off
off
off
On
Q222
off
On
On
off
X201
Live
Live
Live
Dead
X202
Live
Dead
Dead
Live
-26-
A7-A
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