Front End Fv (Fv Part); The Front End Comprises The Following Parts; The Front End Has Been Designed To Receive The Following Systems; Tuner Modulator (Tumod) - Hitachi VTMX900ECT Manuel D'entretien

5. Front end FV (FV part)

5.1 The front end comprises the following parts :

•
TUMOD = Tuner (+ Modulator Option) (+Booster Option)
(+Passive Loop Through Option)
•
IF amplifier & video demodulator IC TDA 9817, [7705] with FM
- PLL demodulator
•
IF amplifier & video demodulator IC TDA 9818, [7705] with FM
- PLL and AM demodulator
•
FM stereo decoder TDA 9873 [7760]
•
Multi-standard FM stereo, AM, NICAM decoder MSP3415D
[7761]
5.2 The front end has been designed to receive
the following systems:
•
PAL B/G with FM stereo
•
PAL 1 or PAL BG with NICAM stereo
•
PAL BG with NICAM and FM stereo
•
PAL BG/I SECAM L/L' with NICAM and FM stereo
•
PAL BG SECAM DK with NICAM and FM stereo
•
PAL B/G
•
PAL I
•
PAL I Ireland
•
SECAM L,L', PAL BG/I
•
PAL B/G, SECAM DK
The relevant layout is given in the version list on the circuit dia-
gram.

5.3 Tuner modulator (TUMOD)

The tuner and modulator are fitted into the same housing.
Both the tuner and the modulator are PLL-controlled. The reception
frequency or modulator frequency is set using the IIC bus.
The amplification is determined by the AGC voltage at pin 5 [1701]
(for operation, see IF demodulator section).

5.4 IF selection

The IF frequency of the video carrier is 38.9 MHz for all systems
except SECAM L' (33.9 MHz).
For PAL BG-SECAM DK and for PAL BG/I-SECAM L/L´ a quasi-
split audio system is used; i.e. for video and audio carriers, separa-
te surface-wave filters (OFW) are required [1704, 1703]. For all
other standards an intercarrier system is used; i.e. a common OFW
with audio stair-step can be used [1704] for video and audio
carriers.
For the PAL BG/I-SECAM L/L' version, an additional circuit for
suppressing the adjacent channel audio carrier is provided, which
is set using coil [5704] to maximum suppression at 40.4MHz.

5.5 IF demodulator

TDA 9818
The IF signal from the tuner is processed by another demodulator
IC of type TDA 9818 [7705]. The TDA 9818 is 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 dBµV), 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
=/01,/02/16
=/05 Pal I with UHF reception
=/07 Pal I with VHF/UHF reception
=/39
=/58
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').

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
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 I2C bus are available controlled on pins 1 and
2.

6. Video signal processing VS (VS part)

6.1 Switchover functions in the signal electronics
IC LA71595M [7004]:
The signal electronics IC LA71595M [7004] are controlled via the
I2C 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.
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
2-13
2
C bus. This means that the
< 0.8V
= 1.2 ... 3.8V
> 4.2V
GB