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15
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Model No.: 14LAANZACDC
Version: 1.0
d) White balance adjuster
Traditional white balance is adjusted through adjusting the bright and dark balance
potentiometers of the CRT drive circuit. The white balance adjuster of the chassis is
equipped in LA76818A, which is performed by the CPU through the I
2
C bus.
e) Video
amplifier
The video output circuit is amplify three primary colors and drive the CRT to
display color pictures.
V902, V912 and V922 are three end video amplifying triodes. V931, V932, VD901,
VD911, VD921, C901, C911 and C921 are formed into a spot killer.
When the TV operates, 9V supply voltage supplies enough voltage to C932 so that
C905’s negative has lower potential to saturate V931 and its positive has higher
potential to cut off V932. as the positive potential of VD901, VD912, VD922
diodes lower than their negative potentials, the diodes cut off, not affecting the TV’s
operation. When turn-off, C931, C932 and C933 discharge to cut off V932 through
VD902, VD903 and R933, as the electric charge of C934 is discharged quickly due
to its too small capacitance, V932’s emitter is conducted to conduct VD901, VD911
and VD921, ensuring V902, V912 and V922 end video amplifying triodes
conducting for a period of time and high voltage of the CRT discharged quickly
through the end amplifying triodes. Thus spot is killed when turn-off.
3. AUDIO SIGNAL PROCESSOR
The audio signal processor mainly consists of a SIF processor, audio switchover circuit and audio
power amplifier. 14S01 uses LA4285 to complete audio power amplifying.
a) SIF processing and audio switchover circuit.
The detected video signal as well as second SIF signal is output from Pin52 of
LA76818A to be coupled by R122, from which the high pass filter including C125,
C126 and L121 filter out a SIF signal y to be sent to the band pass filter connected
to Pin54. The band pass filter further filters interference elements except
4.5-6.5MHz SIF signals out of the two signals for sent to phase discriminator. In
addition, SIF carrier signal from the SIF carrier signal from the SIF carrier PLL
restorer (SPLL) is also sent to the phase discriminator. After the discriminator
compares the two signals, the filter externally connected to Pin53 filters high
frequency element out of the generated error signal and processes it into DC error
voltage to control oscillating frequency in the SPLL circuit so that the frequency is
always consistent with the received sound IF.
