Service manual

CB-12
CB CIRCUIT DESCRIPTIONS
Jack-Pack
The CB chassis provides multiple means for connecting external sources that supply video and audio signal.
These provisions include two composite video (CV) inputs, two S-Video (Y/C) inputs, component video
(YUV) input, corresponding left and right channel audio inputs for each video input, and, in some models, a
front input jack featuring CV, Y/C, and stereo audio inputs. Additionally, a two-channel variable audio
output is provided. This portion is discussed further in the audio circuit description.
Audio/Video Switch IC
In order to handle the multitude of incoming signals from the jack-pack, as well as the two internal IF
signals, the CB chassis employs an analog audio/video IC2900. This IC is powered at pin 18 by the
+9VSW. While switching is analog, IC2900 is digitally controlled through the I
2
C (serial clock and data)
bus connection at pins 26 and 27. This data stream communicates both user selections for signal input as
well as microprocessor priority commands. These priority directives may be explained by the following
example.
<<Figure CB-11>>
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
36
26
27 28
29
30
31
32
33
34
35
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
LINE2
VINE2
RINE2
LINE1
VINE1
RINE1
LINE4
VINE4
RINE4
VINE3
LINE3
RINE3
VINS1
LINS1
YINS1
RINS1
CINS1
GND1 ROUT1
YOUT1
LOUT1
VOUT1
YIN1
CLAMP1
VINS2
LINS2
YINS2
RINS2
CINS2
VCC CLAMP2
YIN2
ROUTD
LOUTD
CIN1
COUT1
VINS3
LINS3
YINS3
CINS3
RINS3
GND2
MUTE CIN2
O3
COUT2
ROUT2
YOUT2
LOUT2
VOUT2
SDA
SCL
I/O2
I/O1
IC2900
C2934M
C2930M
C2929M
C2931M
C2928M
R2944M
C2933
C2932
R2960M
R2958M
C2927
C2926
C2925
R2945M
R2940
C2924M
C2938M
R2943M
R2933M
C2923M
Q2902
R2934M
R2935M R2936M
+9VSW
Q2904
R2956M
Jumper
R2957M
R2955M
R2937M
R2954M
Q2901
R2938M R2939M
+9VSW
+9VSWF
Q2903
R2952M R2953M
IF2-Video
CV-Micro
IF-Video-Main
Y+C/CV-PiP
Luma-Main
Luma-SD
Left-SW
Right-SW
Y-Comb
CV-Comb
C-Comb
Chroma-Main
1 2 3
4 5 6 7 8 9
R2931M
R2932M
ZD2903
R2930
Y/C-Front-Sense
C2922M
C2921M
C2913
R2924
C2919M
PROV
C2914
R2925
R2973M
C2917M
PROV
C2920M
R2928
C2916
R2926
R2974MZD2908
R2927
Jumper
C2918M
PROV
C2915
R2923
ZD2903
C2901
R2902 Jumper
ZD2904
R2901
C2902
R2904
R2969M
C2905M
C2903
R2906
R2970M
Y/C1-Sense
SDA
SCL
R2907
ZD2901
Y/C2-Sense
C2907
R2909Jumper
C2908M
R2911
R2910
R2908
ZD2906
+9VSW
C2912
C2937
R2914 Jumper
ZD2905
R2916
C2906
C2910
R2921 Jumper
R2918
C2909
C2911M
R2922
R2919
R2912
R2971M
R2972M
ZD2910
R2920M
See Component Video
JackPack Section
11
23
18
6
5
4
10
2
19
9
8
3
7
17
12
7
24
12
24
17
Y/C1-In
Aux1-R-In
Aux1-L-In
Video1-In
Y/C2-In
Aux2-R-In
Aux2-L-In
Video2-In
4A8
IQB27B42W
IQB27B44W
IQB36B44W
ONLY