Philips DVDR1000/001, Service Manual

Page: 161 / 317

Circuit-, IC Descriptions and List of Abbreviations
GB 161 DVDR1000 /0x1 /691 9.
and will reach approx. 10V at a temperature of 40 ° C. It is also
possible to switch off the fan via the control line ION_FAN.
The circuit generates also two control-signals: TEMP goes to
the P and BE_FAN is the control-line for the basic engine fan.
9.3.7 Power Supply
The 5SW and 8SW supply are switched off in case of standby
from the P via the ISTBY-line. This is possible for power-
save. The ISTBY-line must be low in case of STBY. There is
also a
„ power fail “ circuit on the PS-schematic which is
necessary to mute AUDIO when IPFAIL is low.
9.3.8 Front End (TU, AP Part)
The Front End Comprises the Following Parts:
•
Tuner [1705]
• IF amplifier & video demodulator IC TDA 9818 [7703]
• Sound processor MSP3415G [7600]
IF Selection
The IF frequency of the video carrier is 38.9 MHz for all
systems except SECAM L' (33.9 MHz).
A quasi-split audio system is used. Separate surface-wave
filters (SAW) are required. [1700], [1701] for video, [1702] for
audio. [1700] Is switched into the signal path for DK/I-
SECAM L/L' reception, if the signal SAWS is
“ high ” . In this
case the switches [7701], [7702] are open and the diode
[6700] is conducting. [1701] Is switched into the signal path
for BG reception, if the signal SAWS is
“ low ” . Then the switch
[7708] is open and the diode [6701] is conducting. For DK/I-
SECAM L/L' reception, an additional circuit for suppressing
the adjacent channel audio carrier is provided, which is set
using coil [5702] to maximum suppression at 40.4MHz.
IF Demodulator
TDA 9818
The IF signal from the tuner is processed by the demodulator
IC TDA 9818 [7703]. The signal PSS to pin3 switches
between demodulation of positive SECAM or negative PAL
modulated video carriers. A QSS-audio-IF signal SIF1 is
generated for demodulation in the sound processor [7600].
The audio-IF carrier is selected in the audio SAW filter
[1702]. This filter is switched for SECAM L
’ . If the signal SB1
is “ high ” , the switch [7707] is closed and the diode [6702] is
not conducting. For all other standards the diode [6702] is
conducting and the switch [7707] is open. The output signal
from this SAW filter is first processed in the TDA 9818. Audio
carriers are converted from the tuner IF level into the audio
IF position and further processed in the audio demodulator
[7600]. The AFC coil [5703] on the TDA 9818 is adjusted so
that when a frequency of 38.90 MHz is supplied to the IF
output of the tuner, the AFC voltage on pin 17 of 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 resistor [3702] to earth. The switch [7700] and
the signal SB1 "high" do this. The HF-AGC is set using the
AGC controller [3707] so that, with a sufficiently large
antenna input signal (74 dBV), the voltage at the IF output of
the tuner [1705] pin 11 is 500 mVpp. This setting must be
carried out, when the audio carrier is switched off. The
demodulated video signal appears on pin 16 [7703]. The
demodulator AGC voltage at pin4 is used to determine the
antenna signal strength after a buffer [7705] with the signal
AGC_MUTE. In the opposite direction this line may be used
to mute the demodulator to avoid cross talk in all cases,
where the tuner signal is not needed. In this case a
„ high “
signal is sent via AGC_MUTE and the conducting diode
[6703] to pin4. The video trap [1703] reduces adjacent
channel video and sound carrier remainders in the video for
BG standards. For all other standards the switch [7704] and
signal TS "low" bypass this trap. In this cases the selectivity
of the SAW filter [1700] is sufficient. A frequency response
correction is achieved by the inductance [5009] for not BG
standards. This correction is not preferred for SECAM L' and
therefore shorts circuited by [7709], if the signal SB1 is
“ high ” . The demodulated video signal VFV is available after
the buffer and limiting stage for noise peaks [7706]. The FM-
PLL demodulator function of TDA 9818 is not used and
deactivated by the resistor [3726].
Audio Demodulator
Sound processor MSP 3415G
The MSP 3415G [7600] is a multistandard 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 are 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 I2C bus. The audio signal
from the tuner is available at the pins 30 AFER and 31 AFEL.
9.3.9 Input/Output Video-Routing (Europe-Version)
General Description:
The complete Video- I/O-switching is basically realised by
the I/O switch STV6410A. It is controlled via IIC-Bus-0 (SDA/
SCL) by the all in one C on the analogue board. The STV
6410 has three YCVBS switches, three chroma switches and
one RGB switch. All switches have 6-dB amplification on the
outputs. The YCVBS inputs have bottom clamp, the chroma
inputs have average clamp, and the RGB inputs have bottom
clamp circuits at the inputs. The R/C inputs can be switched
to average clamp for chroma signals via I2C bus.
The IC has also one slow blanking monitor and one fast
blanking switch for fast RGB insertion (see detailed
description in chapter 1.5). Two pre-selectors BA 7652 are
additionally used: One for switching between Rear CVBS, Y-
Rear and Front, the second for switching between Chroma-
Rear and Front signal. Both pre-selectors are controlled via
IS1 and IS2 from the analogue board C.
CVBS Signals:
There are four CVBS input connection possibilities: Front
chinch (E6), Rear Chinch (E4), Scart 1 (E1) and Scart 2 (E2).
Rear Chinch In is routed via the pre selector BA 7652; the
other signals are connected direct to the STV 6410. The
selected CVBS signal is routed to Rear Chinch Out (via BA
7660, 6dB amplification, 75 Ohm driver) and to Scart 1.
Independent of the input signal quality (CVBS, S-Video or
RGB) the digital board supplies also S-Video and RGB
signals to the corresponding socket.
S-Video Signals:
There are also four S-Video input connection possibilities:
Front In (E5), Rear In (E3), Scart 1 and Scart 2. For S-Video
from Scart this option has to be switched on in the OSD
menu. The pre-selectors and the STV 6410 do the signal
selection (for detailed routing see overview). Also the video
quality will be S-Video, the digital board supplies also CVBS
to the corresponding sockets. The S-Video signal that is
coming from the digital board is routed via BA 7660 (6-dB
amplification and 75-Ohm driver) to the S-Video Rear Out
socket.
RGB Signals:
The Scart 2 RGB input signal (Decoder socket) is connected
to the RGB switch of STV 6410 and to the digital board in
parallel. The RGB from Scart 2 is routed to Scart 1 in low