Service manual

CA-23
Audio Development
In the mono circuit, composite audio is fed directly from pin 2 of ICX2200 into the audio amplifier circuit.
However, on stereo and MTS models, composite audio is fed into IC1400A or IC1400 respectively. Here
the composite sound can be separated into left and right audio channels.
Stereo Processing
In stereo receivers, IC1400A receives composite audio through C1436 into pin 11. Because the 490
mVrms composite audio signal from ICX2200 is too high for the audio processor input, the voltage divider
consisting of R1421M and R1422M limit the signal to 245mVrms. This audio processor is controlled by
the microprocessor via serial clock and data lines connected at pins 3 and 4. IC1400A is powered by the
+9VSW at pin 16. Its right and left channel output exit the IC at pins 1 and 2.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
LSOUT-R
LSOUT-L
SDA
SCL
DGND
MAININ
MAINOUT
PCINT1
PCINT2
PLINT
COMPIN
VGA
IREF
GND
SAPTCVCC
SUBOUT
STIN
NDISETC
SAPOUT
SAPIN
VE
VEWGT
VETC
VEOUT
VCAIN
VCATC
VCAWGT
NC
NC
IC1400A
C1415
R1405M
C1414
C1417
C1419
C1422
R1407M
C1424
R1408M
C1428
C1426
C1427
+9VSW
C1433M
C1430
R1425M
C1421
C1420R1406M
C1416
C1425
R1404M
C1413
R1422M
C1436
R1421M
C1418
C1435M
PROV
C1434M
PROV
R1401
R1402
To Audio
Amp IC
Clock &
Data Lines
Composite
AudioInFrom
ICX2200, Pin 2
<<Figure CA-22>>
External audio input on the stereo chassis is passed to the audio amplifier via IC1401, a microprocessor-
controlled switching IC. This IC is powered by the +9VSW at pin 9. When the external inputs are present
on a receiver, processed audio from IC1400A will come into the switching IC at pins 5 and 12. External
(or auxiliary) audio enters the switching IC at pins 7 and 10. If an auxiliary source is detected by IC6000, a
signal from pin 44 of the micro will trigger pins 2 and 4 of IC1401 to switch from internal to external audio
inputs. Whichever audio source is selected will be passed from pins 8 and 11 to the volume control
IC1402.