Service manual

CB-14
CB CIRCUIT DESCRIPTIONS
Component Video
Component video is handled differently than the other jackpack inputs. The CB lacks conversion circuitry
to make component (YUV) signal into CV. For this reason, component video cannot be used for PiP,
which requires CV input, and is furthermore not separated (or combined) into luma and chroma through
IC2900. YUV is directly input to IC2200 at pins 37 through 39. This arrangement necessitates the use of
a YUV switch from the microprocessor to the video IC. With respect to the A/V switch, however, the Y
component is still input to pin 2 and, when in use, is output as composite video to the microprocessor. As
mentioned before, this information is used to obtain CC and video synchrony. Moreover, the U component
must be amplified to an acceptable level to be used by IC2200. Q2906 and 2907 serve this purpose using
the +9VSWF for power.
C2904
C2940
R2905
C2939
R2903
R2976MR2975M
1
2
3
R2946
R2948
R2950
Jumper
R2949
R2951
R2947
ZD2907
1 2 3 4
1 2 3 4
C2941
Q2906
R2961M
R2964M
R2964M
R2963M
C2942
R2965M
+9VSWF
Q2907
C2943
R2966M
R2967M
R2968M
CR-In
YUV-In
CB-In
Pins 1-3
IC2900
A/V Switch
4C2
2C4
151413
24
17 212016
YUV-In Cr-In Cb-In R-In L-In
<<Figure CB-12>>
Comb Filtering
CB receivers use either a 1H glass comb filter, DL2400, or a 2H digital comb filter, IC2400. Both separate
composite video into luma and chroma more efficiently than simple chroma traps and band-pass filters. This
allows for video that is relatively free of color and luma distortion in high detail video objects. Comb filters
are better equipped to distinguish color from high-frequency luma, and can thereby reduce the crosstalk
between the two.
For sets using DL2400, CV from IC2900 enters pin 2. Chroma is output to pin 3 while luma exits the filter
at pin 5. Receivers that possess DL2400 still utilize a color trap (R2470M, L2411, and C2471M) and a
band-pass filter (R2463, L2410, and C2442M) to ensure purity of both chroma and luma before it is
returned to the A/V switch.