Philips 286NS-05, Руководство по обслуживанию

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9 CIRCUIT DESCRIPTION
27 Comet
9.9.11 IF Source Select, Luminance And Chrominance Separation.
The Baseband Video signal (normal amplitude 2Vpp) at Pin 7
also contains the inercarrier sound signal, however the sound
signal has to be filtered out before the Video signal can be used
. Ceramic filter 1102 (6 MHz) is used for this purpose. After the
filter has removed the sound, the Video signal is then fed back
into the IC at Pin13. From here the signal is internally fed to a
source selector switch, Pin16 is used for source select control.
If Pin 16= 0V This is Internal Video Input Mode If Pin 16= 8V
External Video Input Mode Is Selected BIMOS Pin 16 is
controlled via the STATUS and the External 2 switching
signals, which originate from the main microprocessor.
9.9.12 Luminance And Chrominance Separation
The Chrominance signal is filtered out by using a Notch Filter,
the Notch Filter provides -20db of attenuation. The Notch Filter
is accurately internally calibrated by the subcarrier frequency
(4.43 MHz).
9.9.13 Sharpness Control-Pin 14
Picture Sharpness is adjusted at Pin 14 of the BIMOS IC. The
voltage variation expected here will be between 2.5V-5V.
Picture Sharpness is adjusted in the on screen Picture Menu.
9.9.14 Crominance Decoder
The Chrominance signal originating from the CVBS signal (Pin
7) is filtered and then applied back into the BIMOS via either
pins13or15.Pin16
is connected to the Microprocessor (Pin17 ) and is used for
internal/external video switching. The internal Chroma
Decoder is then internally fed with this selected feed, see page
11. From here the Chroma is fed to a pre amplifier and then on
to the Burst Demodulator, the next stage is the R-Y and B-Y
Demodulator. The Line and Frame Oscillators also use the
4.43 MHz reference signal available at pin 35.
9.9.15 Pin 27
Is used for Chroma standards selection, however as these sets
are PAL only this pin is permanently forced in the PAL system
via this pin. To facilitate this 5.5 Volts is applied to this pin via
R3104 and R3145, 4K7.
9.9.16 Pin 32
This pin is used in combination with a separate SECAM
decoder, it is used to select either the PAL or SECAM colour
systems.
For PAL only sets, this pin will be set at 1V5 volts.
9.10 Video Controller Section: RGB-Dematrixing
This block dematrixes the -(R-Y), -(B-Y) and the Y signals into
RGB signals; the Sandcastle pulse, which is derived internally,
synchronises the internal RGB dematrixing process, it is also
used to suppresses the RGB output signals during Frame
Flyback.
9.10.1 Analogue Control
– 0-4V5 /Contrast Pin 25
– 0-5V /Brightness Pin 17
– 0-2V5 /Saturation Pin 26
9.10.2 Fast Blanking
Via the FAST BLANKING signal available at pin 21 RGB input
selection is also made.
9.10.3 OSD FAST BL
Originates from the OSD generator; this signal is "high" (>1V)
to insert OSD characters.
9.10.4 F.BL.SCART
This is the fast blanking signal form pin 16 of Scart 1. This
signal is "high" (>1V) to switch the RGB source select into
external input mode.
Note: Scart 2 does not have RGB capability.
9.10.5 F.BL. TXT
Fast Blanking signal from the Teletext Decoder. This pin is high
(>1V) to switch the RGB source select into external mode. Pin
22 Red, 23 Green and 24 Blue.