Circuit Descriptions, Abbreviation List, and IC Data Sheets
EN 19
TC5.1U CA
9.
9.1.3
Tuning Section
This section mainly consists of the tuner (TU101), the IF pre-
amplifier circuit and the SAWFILTER.
Table 9-1 Tuning section 1
Table 9-2 Short specification of the tuner
From Pin58 of IC101 the I2C bus clock signal goes to the tuner.
The tuner works during the clock time. IC101 will send out a
data signal from Pin57 to control the tuner's working state by
controlling the +33V voltage. +33V is provided from Pin10 of
T803. That voltage is put into the tuner at Pin7. A circuit inside
the tuner tran33V into a voltage between 0 and +33V
(as a function of the data, sent by IC101).
The AGC signal is a close loop control voltage that keeps the
amplitude of the signal constant.
Output of tuner is the Intermediate Frequency signal (IF signal).
The IF signal will pass pre-amplifier circuit (refer to the picture
below). The amplified IF signal passes the SAW filter and is
then sent to IC101 Pin41/42.
IC101 creates a CVBS signal and sends it out from Pin30.
CVBS will be selected by IC901, and then pass from Pin13 of
IC901 to Pin20/24 if IC101. IC101 will demodulate the CVBS
signal into an R, G, B signal. Next IC101 will send this R, G, B
signal from Pin50/51/52 to the CRT board.
Figure 9-3 Pre-amplifier circuit
9.1.4
Sound Process Section
The SIF signal is sent out together with the TV signal from
Pin30 of IC101. It passes through Q203, R225. X202 and a
High-pass filter (consisting of C254, L206, C253) filters out the
video signal and low frequency interference.
Figure 9-4 Sound process section 1
SIF will be finally sent into Pin2 of IC1001. An analog automatic
gain control circuit (AGC) allows a wide range of input levels.
The analog-to-digital conversion of the IF sound signal is done
by an A/D-converter. The high pass filter, formed by a coupling
capacitor at suppresses video components.
IC1001 is controlled via the I2C bus slave interface.
The AV sound signal will be directly sent to Pin37/38 or Pin40/
41 of IC1001. Q901/2 and Q903/4 form Emitter-Follower
circuits to provide a better load ability.
The (analog) sound signal will go from Pin26/27 of IC1001 to
Pin4/12 of IC602. IC602 is a dual bridge amplifier. The output
voltage of IC602 drives the speakers. The volume is adjusted
via the I2C bus.
Figure 9-5 Sound process section 2
Pin
Symbol
Description
1
AGC
Auto gain control
2
AS
I2C bus address select
3
SCL
I2C bus serial clock
4
SDA
I2C bus serial data
5
6
BP
Supply voltage tuner s5V
7
BT
Supply voltage tuning s31V
8
IF
Intermediate frequency out
Receiving
Channel
VHF LOW BAND: CH2~B(55.25~127.25MHz)
VHF HIGH BAND: CH C~CH W+11(133.25~361.25MHz)
CH W+12~69(367.25~801.25MHz)
Receiving
System
NTSC
Intermediate
Frequency
Picture carrier: 47.74MHz
Colour carrier: 42.17MHz
Sound carrier: 41.25MHz
Antenna Input
Impedance
Unbalanced 75Ohms
Output Imped-
ance
Unbalanced 75Ohms
Band change-
over system
Digital change by PLL IC
G_16340_023.eps
100306
G_16340_024.eps
100306
G_16340_025.eps
100306
