Haier 29T9D, Service Manual, Page: 45 / 73

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30 Post-AV audio input of right channel 4.0 4.6M 3.2M
31 Woofer control 4.4 6.9M 4.8M
32 Pre-AV audio input of right channel 4.0 4.6M 3.2M
2.6 Analysis of sound amplifying circuit
The sound amplifying circuit is comprised of an integrated circuit TDA7297 and peripheral
components. TDA7297 is a double-channel stereo sound amplifying circuit featuring MUTE and
POWER functions, with power output 15+15W. TDA7297 has a BTL sound output manner with no
coupling capacitor in its output circuit, which has a wide range of power supply
（
6V
～
18V
）
and the
functions of short circuit protection and over-load protection.
(18) and (15) of the sound tone processing circuit N701 send out the sound signal for left and right
sound channels, which will be adjusted by R604, R603 and 607, R606 respectively , and then
coupled and fed into the (4) and (12) of the sound amplifying integrated circuit N601 via C601 and
C605, and , after being amplified, sent out from the (1), (2) and (14), (15) in positive and negative to
directly drive speakers for sound.
Woofer amplification is also comprised of the integrated circuit TDA7297 and peripheral components.
The sound signals from left and right channels that have not passed through sound tone processing,
will be coupled and fed into the (12) of N610 via C611, which, after being amplified, will be sent out
as positive and negative to directly drive speakers for sound.
Table 4 lists the pin functions and test data of TDA7297as the reference for maintenance. The data is
to be tested under the mode of 49.75MHz
，
PAL D/K and cylindrical color card, using a model FLUKE
79
Ⅲ
instrument.
Table 4
Resistance to Ground R
Pin Function
Working
Voltage
（
V
）
Forward Test
（Ω）
Back
Test
（Ω）
1 Sound output from right channel 8.0 12.8K 12.7K
2 Sound output from right channel 8.0 12.8K 12.8K
3 15V Power supply 16.0 ~ 0.94M
4 Audio signal input of right channel 1.5 86.2K 86.6K
5 Blank pin 0 ~ ~
6 MUTE signal input 5.1 108.8K 107.6K
7 POWER signal input 5.1 5.6K 5.6K
8 Ground 0 0 0
9 Ground 0 0 0
10 Blank pin 0 ~ ~
11 Blank pin 0 ~ ~
12 Audio signal input of left channel 1.5 86.3K 86.5K
13 15V Power supply 16.0 ~ 0.94M
14 Sound output from left channel 8.2 12.7K 12.7K
15 Sound output from left channel 8.2 12.7K 12.7K
Table 5 lists the pin functions and test data of woofer TDA7297as the reference for maintenance.
Circuit Explanation