Osd/Follow Tv (Os/Fome) - Grundig GV 6400 HiFi/5 Service Manual

GV 6400 ..., GV 6401 NIC
2.7 Family Board – OSD/Follow TV (OS/FOME)
General Information on OSD
The IC7800 makes it possible to display a full page with separate
background (Full Page) and to insert information into the playback or
(EE) signal (Superimpose). For this purpose IC7800 is fitted with a
programmed Character-ROM containing 128 characters. The FSC
signal from the Video/Chroma circuit stage passes through the fre-
quency doubler (T7830 / L5831 / D6830) for the background of the
OSD information including the sync signal generation (without line
interlacing).
The integrated Display-RAM of IC7800 allows to display 12 lines of 24
characters each. This memory reads in the character codes supplied
via the 3-lead bus IC7800-(9/10/11). Separate registers determine the
position of the display and the background. Each character consists of
a 12x18 dot matrix the vertical size of which is determined by the line
scanning pattern. The width of the character is determined by the LC
oscillator at IC7800-(6/7). This oscillator operates at a frequency of
6.59MHz (±2%) and is synchronized by the horizontal pulses (CSYNC)
from IC7800-(17) when information is superimposed, or by internally
generated horizontal pulses when a full page on blue background is
displayed. Due to this method, the character read-out rate and the
background are definitely coordinated. Counters which are triggered
by the horizontal frequency and the LC oscillator are used for address-
ing the display-RAM. The integrated character-ROM converts the
character codes to pixels.
OSD Signal Path
The playback or loop-through signal is fed through the impedance
converter T7821 to IC7800-(15). The insertion of information into the
signal is made in the "MIX" stage. Afterwards the signal is passed
through IC7800-(13) and the impedance matching stage T7802 to the
"IN/OUT" circuit stage.
The vertical synchronization of the superimposed display is effected
externally by the field pulse "OFP" at IC7800-(20), and the "CSYNC"
signal at IC7800-(17) takes over the horizontal synchronization of the
display.
Follow TV
For the "Follow-TV" function (option) the video signals from the
EURO-AV1 (VIN1) socket are compared with the signal from the
Frontend (VFV). The resulting signal is the so-called "FOME" signal.
In the sync separators "4-C" and "4-D" of IC7850 the sync levels of
each input signal are separated from the video signals. The transistors
T7851 / T7852 form an Exclusive-NOR gate which sends a HIGH level
to the Schmitt-Trigger "4-B" of IC7850 if the sync signals are synchro-
nous. The trigger inverts the level and passes it on as a "FOME" signal
(active at LOW level) to the deck computer IC7400-(1).
3. Family Board II (PAF)
3.1 Family Board II – Stereo/NICAM Decoder (SD)
The Stereo/NICAM decoder has the task of amplifying and decoding
the signals (ALR, A2R and SSIF) coming in from the Frontend. It
produces the following AF signals:
– Stereo sound: Left: AF1; Right: AF2
– Two channel sound: Sound 1: AF1; Sound 2: AF2
Stereo Decoder (SD)
Mono Sound
On Mono broadcasts, a signal (ALR) is present only at IC7780-(7). The
evaluation circuit in the decoder IC7780 identifies the MONO status
and advises the keyboard control computer IC7201 correspondingly
via the I 2 C bus (pins 1/20). Via the I
selection switches in IC7780 to MONO and the sound signal is
connected to the output pins 13 / 14. From there, the signal is taken to
the Audio circuit section.
Stereo Sound
On Stereo broadcasts the sum signal
and the R-signal (A2R) with pilot tone (117Hz amplitude modulated) is
present on pin 8. Via the pilot circuit (C2783 / L5780) and pin 5 of
IC7780 the pilot signal is fed to the evaluation circuit. In this circuit the
decoder identifies the stereo status from the presence of the 117Hz
signal and advises the keyboard control computer via the I
computer then controls the matrix in IC7780 via the I
L + R
the signals and R, the Stereo signals L and R are obtained. It also
2
sets the output selection switch to "Stereo". On pins 14 (AF1 - L) and
13 (AF2 - R) the signals are fed out and applied to the Audio circuit
section.
GRUNDIG Service
2 C bus, this computer sets the output
L + R
(ALR) is present on IC7780-(7)
2
2
C bus. This
2 C bus so that from
Two-channel Sound
On two-channel sound broadcasts, the sound channel 1 is present on
IC7780-(10) and the sound channel 2 with pilot tone (274Hz amplitude
modulated) is present on IC7780-(9). By means of the evaluation
circuit the decoder identifies the two-channel status from the 274Hz
signal and advises the keyboard control computer via the I
computer controls the output selection switch via the I
sound channel 1 (pin 12) and sound channel 2 (pin 11) are applied and
connected to the Audio circuit stage.
NICAM Decoder
The NICAM (NEAR INSTANTANEOUS COMPANDED AUDIO MUL-
TIPLEX) Transmission System is a digital stereo sound transmission
technique.
This technique is a standard for sound transmission in television
engineering. Compared to the conventional analog methods, this
technology makes it possible to achieve an appreciable improvement
in the signal-to-noise ratio and the dynamic range.
In a way similar to the analog stereo/ two-channel sound technology
applied in Germany for example, also with NICAM, a digital sound/data
signal with a separate carrier is additionally added to the conventional
vision and sound signal. Apart from two digital sound channels of 10Bit
each this digital signal contains scaling, identification as well as coding
data for stereo, mono, two-channel sound or the data transmission.
The total dynamic input range is divided into eight stages. The so-
called "Scaling Factor" identifies the respective stage and serves as
the multiplication factor for the 10Bit data word. Hence its name.
The scaling factor is determined every 2ms at a sampling rate of 32kHz
and, together with the operational sign-bit, results in a dynamic total of
14Bit. With this method, the data rate is reduced to 704kBit/s compared
to 896kBit/s of a real 14Bit transmission. To conceal this loss of
information, use is made of statistical characteristics of the sound
signal and the properties of the human ear.
Apart from this compressed data transmission, a further advantage of
the Nicam-System is its low sensitivity to interference due to the use
of 4PSK-Modulation (Phase Shift Keying). This improvement in quality
requires, however, an even more sophisticated design of the transmit-
ter as well as of the receiver.
To get a more detailed idea of this system than is possible with this brief
description please refer to the appropriate literature.
NICAM Signal Processing
The sound-IF-signal "SSIF" is fed through solder contact 1970-(8) to
IC7700-(29). In IC7700, the signal passes through a bandpass, a gain
controlled amplifier and a mixing stage with QPSK demodulator. The
phase detector corrects the differences between the "CARRIER-VCO"
and NICAM-IF frequency. The integrated "DATA SLICER" generates
the digital signals from the NICAM-IF signal. In the "BIT RATE CLOCK
RECOVERY" stage the original data clock is produced. This stage is
followed by the NICAM decoder, the controller and the deemphasis
stage (digital filter J17). Subsequently, the processed signals are taken
to the D/A-converters (DAC R and DAC L). The analog signals (left -
IC7700-(15) / right - IC7700-(8)) are each subjected to an operational
amplifier (IC7701) where they are filtered and adjusted in level. The
analog signals are then fed through IC7780-(9/10), the source selec-
tion switches and IC7780-(14/13) to the Audio circuit stage as "AF1/2
signals".
The evaluation of the NICAM status (2 mono channels – two-channel
sound, 1 mono channel / 1 data channel, stereo and NICAM-sound =
analog sound) is carried out in the controller interface of IC7700.
3.2 Family Board II – Audio (AF)
The Audio circuit section processes the audio signals for both helicalscan
(FM sound) and longitudianl recording (Standard sound). The heart of
this processing stage forms IC7100 which is controlled by the key-
board control computer IC7201 via the I
3.2.1 Family Board II – FM Sound
As the stereo sound channels are symmetrically constructed, the
description is confined to the left channel (L).
Function Overview
In the FM sound circuit stage, on record mode, the audio signals are
selected by the input selection switch and compressed. Subsequently,
the two carrier frequencies (1.4MHz-Left Channel and 1.8MHz-Right
Channel) are frequency-modulated with the audio signals and fed to
the two rotating audio heads to be recorded onto the tape.
Descriptions
2 C bus. This
2
C-bus so that
2 C-bus.
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