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Video switching functions are carried out in IC501 which is controlled by the IC bus and in analogue
multiplexes I302, I303 and I304, controlled by pins 3 and 4 of I003, (the Microcontroller).
The CVBS at the emitter of Q505 is applied to a 5.5MHz sound trap (CL model only), F501, via R541 which
in turn is applied to the base of Q507. The CVBS at the emitter of Q507 is output at pin 19 of SCART 1
and applied to pin 13 of I501 via R539 and C581. The video signal at SCART 1 is derived from the signal
received by the tuner and is independent of the picture displayed.
SCART 1 has CVBS input and output and luminance & chrominance inputs. The video signal at pin 20 of
SCART 1 is applied to pin 11 of I501 via analogue switch I302, pins 1 and 15, which is switched when pin
10 is high, (3.3V). Luminance and chrominance signals are input at pins 20 and 15 of SCART 1
respectively. The luminance signal is applied to pin 11 of I501 as above and the chrominance is applied to
pin 10 of I501 via analogue switch I302, pins 13 and 14, which is switched when pin 11 is high.
SCART 2 has CVBS inputs, output and RGB input. CVBS input at pin 20 of SCART 2 is applied to pin 17
of I501 via analogue switch I302, pins 3 and 4, which is switched when pin 9 is high. The CVBS output at
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pin 19 of SCART 2 is provided from pin 38 of I501 via R546 and Q508; this is switched by the IC bus and
is identical to the picture on screen. RGB inputs on pins 15, 11 and 7 respectively of SCART 2 are
switched by analogue switch I303. This device switches the RGB inputs to pins 32, 30 and 31 respectively,
of I501, between SCART 2 and SCART 4; or SCART 2 and the DDT module on DDT models. When pins 9,
10 and 11 of I303 are high, the RGB signals are applied from SCART 2; else they are applied from SCART
4/DDT. RGB Blanking is switched between SCART 2 and SCART 4/DDT by I304, pins 3, 4 and 5. When
pin 9 of I304 is high SCART 2 is selected, else SCART 4 is selected.
SCART 4 has a CVBS input but no CVBS output, and RGB inputs. The RGB input functions in the same
way as SCART 2, as described above. The CVBS input at pin 20 of SCART 4 is applied to 17 of I501 via
analogue switch I302, pins 4 and 5, switched when pin 9 is low.
Note, for DDT models SCART 4 is not fitted and the CVBS signal from DDT module is applied to pin 5 of
I302.
SCART 3, front AV3, is used for S-VHS input having separate luminance & chrominance signals and
CVBS. Analogue switch I302 switches the source of the luminance & chrominance signals to I501 pins 11
and 10, from SCART 1 to AV3. This happens when pin 10 and 11 of I302 are low. The CVBS input at front
AV3 phono socket is applied to pin 11 of I501 via I302, pins 2 and 15, switched when pins 10 and 11 of
I302 are low.
The DDT module has two CVBS outputs and one RGB output, some of which have been discussed. The R,
G and B outputs are used for picture content and CVBS OUT1, applied at pin 3 of lead header PL2, is used
for sync purposes. CVBS DT2 is applied to pin 5 of LP2 and in turn pin 5 of I302, only when material
viewed by the digital module is not right protected. Thus, protected material is not output at SCART 2.
The CVBS output at pin 38 of I501 is also input at pin 12 of I003, (Microcontroller,)
for Teletext, VPS and WSS slicing, via Q509. Pins 23, 24 and 25 are the RGB inputs
of I501 used for OSD and teletext display.
The final video signal is output from I501 as RGB on pins 21, 20 and 19
respectively. These signals are applied to the CRT base via R534, R535 and R536.
Video/Chroma TV Input Processor - Philips TDA8879
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The TDA8879 is a multi-standard IC bus controlled TV processor. It contains integrated sound trap
circuits, switchable group delay correction, multi-standard colour decoder with switchable colour filters and
delay line and various picture improvement features including:
Video dependent coring. The coring can be activated only in the low-light parts of the screen. This
effectively reduces noise while having maximum peaking in the bright parts of the picture.
Colour Transient Improvement (CTI). This circuit improves the rise and fall times of colour difference
signals. The function is realised by using delay cells with a length of 300ns.
Black-stretch. This circuit corrects the black level for incoming video signals that have a deviation between
the black level and blanking level. The time constant for the black stretcher is realised internally.
Blue-stretch. This circuit is intended to shift colour near ?white? with sufficient contrast values towards more
blue to obtain a brighter impression of the picture.
White-stretch. This function adapts the transfer characteristic of the luminance amplifier in a non-linear way
dependent on the picture content. The system operates such that maximum stretching is obtained when
signals with a low video level are received. For brighter a picture the stretching is not active.
Dynamic Skin Tone control (DST). This function is realised on the YUV signals by detecting the colours
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near to skin tone. The correction angle is controlled via the IC bus.
Video dependent coring and peaking, CTI, Black-Stretch and DST can be turned on and off by selecting
the ?more? option in the ?picture? menu. Video dependent coring and peaking is listed as ?noise reduction?.
White-stretch is pertinently turned on and Blue-stretch is turned off. In addition to these features, picture
?tint? can be altered in the ?more? option of the ?picture? menu. This adjusts the gain offsets of the red, green
and blue amplifiers to produce a cooler or warmer picture. |
ACEC
HITACHI
