Video Signal Processing Vs (Vs Part) - Philips VR120 Service Manual

GB 102 9.
used to demodulate pos. or neg. modulated video carriers. It
is possible to generate a QSS-audio-IF signal or an
intercarrier IF signal for demodulation in the audio
demodulator [7761]. For the best possible video signal
performance the IF signal is conveyed via an OFW [1704]
according to the standard. The audio-IF carrier is selected in
the audio OFW [1703] which is switched for SECAM L'. The
output signal for this OFW is further processed in the TDA
9818. FM carriers are converted from the IF level into the
audio IF position and further processed in the audio
demodulator. The AFC coil [5702] on the TDA 9818 is
adjusted so that when a frequency of 38.9 MHz is supplied to
the IF output of the tuner, the AFC voltage on pin 17 on the
TDA 9818 is 2.5V. The setting of the picture carrier frequency
for SECAM L in the TDA 9818 is achieved by connecting pin
7 of the IC via a potentiometer [3730] to earth. The AFC
voltage on pin 17 TDA 9818 should then also be 2.5V at 33.9
MHz. The HF-AGC is set using the AGC controller [3707] so
that with a sufficiently large input signal (74 dBV), the voltage
at the IF output on the tuner [1701, pin 17] is 550 mVpp. The
setting must be carried out when the audio carrier is switched
off. The demodulated video signal appears on pin 16 [7705].
The video drop [1705] reduces adjacent channel sound
carrier and sound carrier remainders in the video.
TDA 9817
As for TDA9818, without the option for processing AM audio
and positive video modulation (SECAM L,L').
9.5.6 Audio demodulator
Multi-standard audio processor MSP 3415D
The MSP 3415D [7761] is a multi-standard sound processor
which can demodulate FM Mono/Stereo, NICAM and AM
signals. The incoming signal is first controlled and then
digitised. The digital signal is then demodulated in 2 separate
channels. In the first MSP channel, FM and NICAM (B/G/I/D/
K) are demodulated, whereas in the second MSP channel,
FM and AM is demodulated again (NICAM L corresponds to
NICAM B/G). These demodulated signals are selected
digitally in the I/O and switched to the D/A converter on the
outputs. Amplitude and bandwidth of the demodulated audio
signals can be determined in the MSP using the
corresponding commands via the I
the setting required for the best possible performance can be
made.
FM stereo audio decoder TDA 9873
The TDA 9873 [7760] is a multi-standard A2 audio processor
which can demodulate FM mono/stereo signals. The audio IF
SIF2 is passed from pin 3 [7705] to pin 25 [7760]. The
demodulated stereo signals AFL and AFR I
available controlled on pins 1 and 2.
9.6

Video signal processing VS (VS part)

9.6.1 Switchover functions in the signal electronics IC
LA71695xM [7004]:
The signal electronics IC LA71595M [7004] are controlled via
2
the I C Bus on pins 23 and 24 by the AIO.
As groups 5 and 6 can only be transferred with a change in
HP1, it must be ensured that during measurements the HP1
line is always connected to the SE IC or replaced by a
corresponding signal.
REC/PB via IIC bus
During RECORD pin 30 must be passed via [7009] on 5V
(IREV=LOW) to activate the video write current stages. To
keep the transient condition of the write current as short as
possible, the signal electronics IC is set to REC via IIC bus
before the pin 30 change.
VR120 Circuit descriptions and List of abbreviations
2
C bus. This means that
2
C bus are
PAL/SECAM/MESECAM/NTSC via IIC bus
SP/LP/SLP via IIC bus
VIDEO INPUT SELECTOR SWITCH via IIC bus
In 1-scart units a distinction is made via the IIC bus between
VFV (pin 36 / VID2) and VBS which corresponds to VIN1 (pin
38 / VID1). In 2-scart units the video input selection is made
via IIC bus in the STV6401 [7904] and the SE IC is always on
VBS (pin 38 / VIN1).
VIDEO ENTRY
The feature frame pulse FFP signal on pin 26 is used to enter
the artificial picture pulse for playback features and the test
picture for the unit installation procedure:
Loop through
Test picture
Artificial picture pulse
LP/SP head pair switchover
The switchover between the long play LP head pair and the
standard play SP head pair is made via the HSC signal (pin
25).
4/x scanner in play back:SP head pair:1.2V <= HSC <= 2.8V
2/x scanner in play back:always
Head switchover
The video head switchover is made using the HP1 signal (pin
11). To keep audio linear interference as low as possible, the
HP1 polarity should be selected to be inverse and the HP1
level should be the same as the CROT signal on pin 10.
PB: SP1 / LP1:
SP2 / LP2:
Envelope curve comparator
If the ENVC signal (pin 94) is HIGH, the FM envelope curve
on the LP head is greater than that on the SP head, and vice
versa.
9.6.2 Recording
Luminance
The input signal (1-scart: pin 38 = scart , pin 36 = front end;
2-scart: pin 38 = input video selected using STV6401) is
connected in the IC [7004] and is available uncontrolled on
pin 32 as VREC (SECAM; VPS only unit data slicers). It
reaches pin 31 via an electrolytic capacitor [2036]. In the IC
[7004] the video signal first goes through an amplification
control process (time constants determined by C [2035]).
After the AGC the video signal reaches the FBC clamping
stage (feed back clamp), then the video signal is divided onto
3 paths:
• Loop-through signal path: The video signal is amplified
by 6dB following video entry and is available controlled
on pin 29 as a VSB signal (OSD entry, data slicer -> I/O,
front end,..).
< 0.8V
= 1.2 ... 3.8V
> 4.2V
LP head pair: 0V<= HSC <= 0.8V
3.2V <= HSC <= 5V
1.2V <= HP1 <= 2.8V
0V <= HP1 <= 0.8V