Service manual

CB-13
A/V Switching
Suppose the user has composite video connected to the Video 1 input and S-Video connected to the S-
Video 1 input. If the user selects video source 1 in the customer menu, the receiver must choose between
the CV and the Y/C signal. Each Y/C input has a sensor line that feeds the micro. If the micro detects the
presence of Y/C on video 1, IC6000 will direct the A/V switch to use that Y/C signal instead of the CV.
Thus if it is present, Y/C has priority over CV.
IC2900 features three functional input arrays for jack-pack signal. Each array consists of left and right (L/
R) channel audio input, CV input, and Y/C input. Additionally, the A/V switching IC provides another input
for the dual IF-video signals and input for the Y (luma) portion of the component video input as well as its
associated audio. CV, Y, and IF inputs should scope near 1.0Vp-p. Color burst from the Y/C inputs as
well as audio inputs should scope about 300 mVp-p.
For outputs, IC2900 uses pins 39 and 41 for L/R channel external audio. This is fed to IC1400, the audio
processor and is used if the user selects a jackpack source. Pin 41 serves as the PiP video output. PiP
video is sent as a composite video signal. However, if the PiP source is S-Video, IC2900 internally com-
bines the Y and C signals into a CV signal. PiP CV should have a strength of 2.0 Vp-p at pin 41. Main
video is output to the video processor on pins 32 and 34 as chroma (C) and luma (Y), respectively. The
luma signal should be 2.0 Vp-p while chroma is about 600 mVp-p.
Composite or IF video input to the IC cannot be passed to IC2200 as composite video. Rather, the A/V
switch passes CV or IF video via pin 41 through the comb filter section, where it is separated into luma and
chroma and returned to pins 38 and 30 of IC2900. Voltage at pin 41 should be 2.0 Vp-p. The separated
signal is then sent to IC2200 as Y and C along the main video lines. It should be mentioned that pin 34 also
sends the luma signal to IC6000 so that closed captioning (CC) and synchrony information can be extracted
from it.
Part Location Part # Notes
DL2400 223-00045 IQB27B42W
IC2400 221-01040 IQB27B44W
IC2900 221-01053 All Models
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