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Front Audio In Compressor
39 38 To SysCon IG401
(control for auto vol)
Rear L 37
Audio Stereo Demux
In R 36 Tone & Vol 40 5 Ext Spkr
IA002 Amp IA502
WB Audio 7 41 3
(from Sound/Pix IF) L
23 22 26 25 7 1
(from Sys- 2 Clk
Con IG401) Dat To Ext
L 6 8 R Spkrs
To 2 Int Spkr 10 To Int
Headphones 12 Amp IA003 4 Spkrs
TX809 Audio Processing Block Diagram
The TX809 audio circuit is comprised of a Stereo De-Multiplexor (IA002) and two
(2) amplifier IC's, IA003 and IA502. IA002 is responsible for decoding the stereo
signal into left and right channels and also provides for tone and volume control.
Amplifier IA003 drives the internal speakers while IA502 provides drive for the
external speakers. IA003 also has an output for the headphones. The stereo
de-multiplexor is controlled by the System Control uC, IG401 via the I2C2 bus.
The wide band (WB) audio from the Sound/Pix IF is input to IA002 pin 7. The
front and rear audio inputs are applied directly to IA002 pins 36 through 39. All
switching and signal selection are accomplished in IA002 via control from the
I2C2 bus. The sound compressor (IA001) serves to compress the audio
dynamic range by minimizing any sudden and undesirable changes in audio
level. The output from the Sound Compressor is a DC control signal that is
applied back to the system control IC, IG401. IG401 then communicates the
desired changes back to IA002 via the I2C2 bus.
If an audio problem is suspected check the following:
1. Check for audio power supplies to audio circuits.
2. Confirm speakers are not shorted or open.
3. If problem appears to be stereo related, inject stereo signal (from generator)
into pin 7 of IA002 and check signal path.
4. If problem is external input related, inject know mono audio signal and check
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