Video/Chroma (Vs) - Grundig GV 6400 HiFi Service Anleitung

Descriptions
Carrier Preparation (PAL/NTSC)
– Record (PAL)
For carrier preparation use is made of a voltage-controlled quartz
oscillator (VXO) in IC7051 the oscillating frequency (4.433619MHz) of
which is determined by the quartz (Q1000) connected to pins 32 and
31. The REC-APC detector compares the phase of the transmitted
burst with that of the VXO and controls the latter accordingly. The
control voltage provided on IC7051-(33) is smoothed by C2004, R3001
and C2005. In addition, an oscillator (321FH VCO) is used which is
integrated in IC7051 and controlled by the synchronizing frequency.
The VCO oscillates at a multiple of the line frequency (321f
corresponds to a frequency of 5.015625MHz. This frequency is divided
by 8 in a 4-phase shifter. Subsequently, it is fed to the sub-converter
(SUB CONV) where it is mixed with the VXO oscillator frequency
(4.433619MHz). The result is the subcarrier frequency of 5.06MHz.
The subcarrier passes through an internal 5.06MHz bandpass (SUB
BPF) and is then fed to the main converter (MAIN CONV).
– Playback (NTSC/PAL)
On playback use is made of the quartz frequency (Q1000 –
4.433619MHz) of the free running XO quartz oscillator as a reference,
and the VCO oscillator. After reconversion of the chroma signal from
627kHz (PAL) or 629kHz (NTSC) to the 4.43MHz subcarrier frequency
the VCO is now synchronised by the burst of the played back chroma
signal. The PB-APC stage generates the control voltage for the VCO
comparing the phase of the quartz oscillator with the phase of the
reconverted 4.43MHz burst. The time constant of the filter circuit which
is connected to IC7051-(37) is determined by C2001, C2002 and
R3000. In the 4-phase shifter, the frequency is divided by 8 and fed to
the sub-converter (SUB CONV) where it is mixed with the XO oscillator
frequency. The result is, among others, the subcarrier frequency of
5.06MHz. The subcarrier is supplied via an internal bandpass filter
(SUB BPF) to the main converter (MAIN CONV).
2.5 Family Board – SECAM L (SE)
Recording
The CCVS signal (VREC) from the "IN/OUT" circuit stage is fed
through the emitter follower T7101 to a stage for chroma selection
(Q5103 / T7100). The selected chroma signal then passes through the
trap circuit (L5102 / C2102 / L5101 / C2101 / R3102) to arrive at
IC7110-(29). The trap circuit increases the selective effect of the
"gaussian filter circuit" (Q5103). Subsequently, the signal passes
through a 15dB amplifier and is then taken via pins 25 and 24 to a
limiting amplifier with a following frequency divider. Dividing the
chroma signal in a ratio of 1:4 this divider generates the necessary
1.1MHz signal for recording which is applied to pin 21 of IC7110. The
bandpass which follows then reduces the harmonics resulting from the
frequency division and the signal is routed to pin 19 of IC7110.
Afterwards, it is subjected to a 10dB amplifier and switched to pin 15.
Between pins 15 and 14, the 1.1MHz signal is fed through an "anti-
gaussian filter circuit" (Q5108). The signal is limited then in IC7110 and
passed via pin 17 to the Video/Chroma circuit stage as "CSR"-signal.
It is then fed through an adjustment control for the SECAM chroma
recording current, R3042 (SECAM-Curr.), to the junction R3035 /
R3039 / R3042 where the signal is added to the Y-signal. The sum
signal (FMRV) is taken via the amplifier stage T7018 / T7019 to the
head amplifier.
Control of the switches in IC7110
On recording, a LOW level (0.7V) is present at the collector of the
transistor T7105. This transistor works like a diode, turns on so that a
voltage of 1.3V is present on IC7110-(23). From this level, the following
detection stage can identify the recording mode and switches all in-
circuit switches to record position.
Playback
On playback, the "uncontrolled FM signal from the tape" (FMPV) is
taken to pin 23 of the IC7110 and is then amplified by 6dB. From pin 21,
the signal is fed via a bandpass to IC7110-(19). Between pins 19 and
18, the obtained 1.1MHz signal passes through a 10dB amplifier; via
pin 16, it is fed to another amplifier in IC7110 whose feedback path
contains an "anti-gaussian filter circuit" (Q5108) which is connected
between pin 14 and pin 16. In the AGC stage following the amplifier,
2 - 12
the signal undergoes an automatic gain control (AGC) and its fre-
quency is doubled (2.2MHz) in the full-wave rectifier "RECTIFIER f x2.
From IC7110-(10), the 2.2MHz signal is fed to the bandpass
(R3126...R3127) which removes disturbing harmonics from the wanted
signal. In another doubling stage which obtains the 2.2MHz signal from
IC7110-(8), a 4.4 MHz signal is generated. This signal is subsequently
amplified by 10dB and is fed to the colour killer via pin 31, the anti-
gaussian filter circuit (Q5100) and pin 32. From IC7110-(1) the 4.4MHz
signal is fed into a bandpass (R3122...C2121) which separates
disturbing harmonics from the wanted signal. The resulting SECAM
chroma signal (CSP) is taken via the impedance converter T7106 to
) which
the Video/Chroma circuit stage, IC7051-(28), where it is added to the
H
CVS-signal.
2.6 Family Board – Head Amplifier (HA)
Function Overview
On record the Head Amplifier has the task of feeding the video and
audio signals to the rotating transformers.The signals are then re-
corded onto the tape by the head wheel.
On playback the signals scanned from the tape are amplified, regu-
lated and passed on for Video/Chroma and Audio processing.
The head amplifier in video recorders fitted with 2 video heads (SP)
contains IC7152, in video recorders with more than 2 video heads (SP/
LP), IC7150 is integrated. The variant fitted with IC7150 is described
below.
Video – Record
The Video-FM-signal "FMRV" from the Video/Chroma processing
stage is fed through IC7150-(19) to the recording stage. Subsequently,
on SP mode, the signal is fed through IC7150-(1), 1915-(8) and on LP
mode, through IC7150-(11), 1915-(5), to the common ends of the
rotating transformers. The transformer windings are ac-grounded to
chassis via the plug contacts 1915-(4/6/7/9) and IC7150-(10/9/3/2).
The record output stages are active on condition that a HIGH level is
present on IC7150-(15).
Audio – Record
From the Audio circuit stage the FM signal is fed to IC7151-(11). In this
IC, the signal passes through an amplifier and is fed via IC7151-(15)
and plug contact 1915-(2) to the common end of the rotating transform-
ers. The two other ends of the transformer are ac-grounded to chassis
by the "RAF" switching voltage from IC7151-(10) via IC7151-(4/6).
Video – Playback
The common ends of the rotating transformers "SP" and "LP" are
connected to RF-chassis via 1915-(8) and IC7150-(1), and via 1915-(5)
und IC7150-(11), respectively. The FM information from the tape is
taken on Standard Play from 1915-(9/7) to the pins 7 and 5 of IC7150,
and on Longplay from 1915-(4/6) to IC7150-(8/4). In IC7150, each of
the signals pass through one amplifier and are then switched by the HI
pulse "SWIN" in the head switching stages depending on the sequence
of the heads to build up the FM signal. In this IC the FM signal is then
present on IC7150-(15) as an uncontrolled (in gain) signal "FMPV" for
Video/Chroma signal processing.
In "LP" mode, the HI pulse "SWIN" is superimposed by a DC voltage.
The FM signal of the LP heads is thus fed through IC7150-(15) to the
Video/Chroma circuit stage.
For all Feature functions (e.g. picture search), the FM signals from the
four heads SH1, SH2, and LH1, LH2 are switched to build up the FM
signal. For this, the FM signals from the SP/LP heads are rectified. In
the following comparator a control voltage ENVC is derived signalling
to the tape deck computer IC7400-(7) which head supplies the highest
amplitude. The tape deck computer then selects the corresponding
head by means of the "SWIN" control signal. The sync signal CSYNC
allows the heads to be switched over only at the end of the line.
Audio – Playback
The common end of the transformers is connected to chassis via plug
contact 1915-(2) and IC7151-(15). The FM signals from the tape are
fed through plug contacts 1915-(1/3) and enter IC7151on pins 4 / 6. In
this IC the signals are subjected to amplifier stages and are then
switched by the HI pulse "HP2" depending on the sequence of the
heads to build up the FM signal. The FM signal passes through an
amplifier stage in IC7151 and is taken from pin 8 to the Audio circuit
stage.
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