Outline; In / Out Terminals; Circuit Operation - Toshiba CN27E90 Technical Training Manual

1. OUTLINE

A/V switching circuit performs change-over of video and
audio signals from tuner and external input. The selecting
operation is controlled by microcomputer through IIC bus.

2. IN / OUT TERMINALS

INNER INPUT U/V Tuner (Main)
U/V Tuner (Sub)
EXTERNAL INPUT VIDEO1
VIDEO2
VIDEO3 (Front)
VIDEO3 (Back)
OUTPUT VIDEO OUTPUT (V, L, R) .................... Excepting CN27E90
AUDIO ON SUB-PICTURE ................... Only for CN32E90, CN35E90, CN35E95

3. CIRCUIT OPERATION

This circuit consists of A/V SW IC; TA1218N (QV01), and
selects signals from U/V tuner (Main), U/V tuner (Sub),
E1, E2 and E3.
3-1 COMPOSITE VIDEO SIGNAL
The selected video signal is output to pin 38 of QV01, and
separated by comb filter into Y and C. The resulted signal
is input to pins 30 and 32 of QV01, and is output to pins 36
and 34 to be supplied to Q501 (V/C/D).
Video signal for sub picture is output to pin 42 of QV01, and
is supplied to PIP unit (ZY01).
3-2 S-VIDEO SIGNAL
When a cable is connected to S-VIDEO terminal, inner
switch of S-VIDEO terminal is shorted to ground to turn off
the transistor (QV05 for VIDEO1 input) for S-VIDEO
terminal detection. Then chroma input terminal (Pin 14 for
VIDEO1 input) of QV01 turns open. From pins 36 and 34
(Y/C output) of QV01, Y/C signal of selected source is
output.
.................................. For sub picture (PIP)
With S-terminal
With S-terminal ........ Excepting CF35E50, CL37E56, CE35E15
.................................. Only for CF35E50, CL37E56, CE35E15
45