Toshiba TLP-711U Technical Training Manual - Page 20
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5 . VIDEO/RGB
5-1. Video Signal Process Circuit
5-1-1. Circuit Configuration
This circuit is composed of the following sections:
• The decode section which demodulates the video sig-
nal to Y color difference signal.
• Video demodulation section consisting of the up-con-
verter section which performs double speed conversion
on Y signal, and the matrix section which demodulates
the signal to RGB signal.
• RGB signal process section which amplifies RGB signals
entered from RGB input terminals and supplies RGB sig-
n a l s t o t h e d i g i t a l s i g n a l p r o c e s s s e c t i o n i n t h e n e x t s t a g e .
• Audio signal process section which switches and am-
plifies the audio signal relating to the video signal.
Fig. 5-1-2 shows the block diagram of the video signal
p r o c e s s c i r c u i t .
5-1-2. Video Signal Demodulation Section
The input signals used for this section are a composite
signal, Y/C signal entered from S terminal and Y, Pb, Pr
signal for Hi-vision, DVD, etc.
The composite signal and Y/C signal are used to identify
the signal mode (NTSC, PAL, SECAM) and demodu-
lated to Y, U and V signal.
The signal mode identification is carried out automati-
cally by QA003 (TDA9141, video/color process IC).
The applicable color modes are NTSC, 4.43 NTSC, PAL
and SECAM.
When the color mode is either of NTSC, 4.43 NTSC or
PAL, Y/C separation is carried out by QA002 (TC9090AN,
Y/C separation IC). Input signal switching IC, QA001
(CXA1855Q, AVSW IC) switches the video signal and
the audio signal at the same time.
After the signal mode is identified by QA003, the R-Y
and B-Y signal demodulated is adjusted in their phases
and levels by QA004 (TDA4665T, 1H delay line) and
developed as U and V signals.
The sync signal is also developed from QA003. The Y, U
and V signals demodulated or a video signal entered as Y,
Pb and Pr signal of NTSC or PAL signal format from a
DVD, etc. are switched in by QA005 (M52055FP, AVSW
IC). Then the signal switched is supplied to the up-
converter circuit in the next stage.
When the Y, Pb and Pr signal, the signal format of which
is different from NTSC and PAL signal used for Hi-
vision system, is entered, QA003 does not identify the
signal mode but supplies the signal directly to the next
stage through the buffer circuit.
In this case, the up-converter does not perform the
double speed conversion process on the signal.
CIRCUIT
QA006 (M52347FP, sync separation IC) separates the
sync signal superimposed on the Y signal at Y, Pb and Pr
signal input and determines the display mode using the
frequency of the sync signal separated by QA006.
5-1-3. Matrix Section
The signal matrix is carried out in QF005, TA1276AN,
which is adaptable for the double speed signal and can
control the matrix factor by using I
The signals entered in this section are as follows:
• Video signal processed the double speed scanning con-
version in the up-converter.
• Video signal not performed double speed scanning con-
version, for high-vision system, etc.
• Video signal of fV=15 Hz supplied from a projection
camera.
The signal has already switched before supplied to the
matrix IC, QF005, so only one video signal selected is
supplied to QF005.
At the same time, the blanking pulse, mask pulse, etc. are
also supplied to QF005.
In QF005, not only matrixing the Y, U and V signal to
RGB signals, but also the user adjustments such as color
density, tint, picture quality correction, etc. other than the
black extension, ABL, etc. are carried out.
5-1-4. Audio Signal Amplification Section
The audio signals are included in each of four video
signals entered (RGB1, RGB2, VIDEO1, VIDEO2). All
audio signals are adaptable to the stereo input system
using a stereo mini-jack.
However, the speaker output signal is monaural.
The audio signal for video system is selected in QA001
and finally develops after switching with the signal on
RGB input side. The volume control is carried out by
QB026, M5222FP, volume control IC. The signal
controlled is amplified to the level to drive a speaker in
QA51, LA4425A, audio output IC.
The output is approx. 2W.
Fig. 5-1-1 Block diagram of audio circuit
5-1
2
C bus.