k
2 - 10
GRUNDIG Service
Descriptions
GV 26 EURO, GV 6000 EURO, GV 6300 EURO
2.4 Family Board – Video/Chroma (VS)
Loop-through Signal Path (EE)
The CCVS signal (VREC) selected in the "IN/OUT" circuit stage is fed
to pin 12 of IC7051. In this circuit, the signal passes through the VIDEO-
AGC-stage, an R/P-switch and, after the video amplifier (VIDEO AMP),
it is fed out from IC7051 on pin 16. Subsequently, the CCVS signal
(VSB) is taken via the amplifier stage T7004 and the "OSD" circuit
stage to the "IN/OUT" circuit stage.
2.4.1 Family Board – Video
Function Overview
On record, the CCVS signal is processed and the luminance signal is
converted to a frequency-modulated signal in the video circuit stage.
On playback, the frequency-modulated signal obtained from the tape
passes through a demodulator, a dropout compensator, an equalizer
stage and the crispening stage. Thereafter, the CVS signal is added to
the chroma signal and fed to the modulator or the EURO-AV-socket.
Record Signal Path
The CCVS signal (VREC) selected in the "IN/OUT" circuit stage is fed
from pin 12 of the IC7051 to the Video-AGC-stage, then passes
through a -6dB attenuator (1/2), an R/P-switch, a clamping stage
(CLAMP), a lowpass filter (Y-LPF), and a few stages which are not
active on record mode. After the R/P-switch the signal is fed out from
the IC7051 on pin 4. At the base of the following amplifier stage T7007
a 4.43MHz trap is provided for suppressing the chroma component of
the CCVS signal. The filtered out CVS signal is fed via an emitter
follower (T7007) and C2027 to IC7051-(5). In this IC, the signal is
subjected to a clamping stage, a DETAIL ENHANCER and the NLE-
stage (non-linear emphasis).
On SP mode the DETAIL ENHANCER and on LP mode also the NLE-
stage is active. The NLE-stage is activated (at LOW level) via
IC7051-(25). The linear pre-emphasis (MAIN EMPH) which follows
increases the high-frequency components of the CVS signal linearly.
This preemphasis is reversed on playback mode. As a result, the
signal-to-noise ratio is improved. The peripheral circuit for the non-
linear network consists of C2075 and R3013 (pin 8), and for the linear
network it is made up of R3014, C2026 and R3015 (pin 7). Via
IC7051-(7) the sync level (R3057) of the luminance signal is adjusted
at the MAIN EMPH stage. The white level cannot be changed. The
luminance signal is then fed to the FM Modulator in IC7051.
The frequency-modulated signal is fed out from pin 2 of IC7051 and is
taken via a low pass filter (T7010) to the junction R3039 / R3042 /
R3035 or R3038 where it is added to the chroma signal. The sum signal
(FMRV) is passed through the amplifier stage T7018 / T7019 to the
head amplifier.
Playback
On playback, the signal from the tape (FMPV) passes through the head
amplifier to a few matching circuits for correction of the frequency
response and the delay time (R3034…T7014). Subsequently, the
signal is fed through the emitter follower T7013 to pin 1 of the IC7051.
In IC7051, the signal path divides. For dropout identification, the signal
from the tape is supplied to the dropout detector (DO DET) which
produces a defined period pulse corresponding to the loss of level, to
setting the programmes. Used with a TV receiver (video recorder in
"Standby" mode), the coded video and audio signals are fed from the
TV through the EURO-AV1 socket and the EURO-AV2 socket to the
Pay-TV-Decoder where the signals are descrambled and then re-
turned to the TV receiver via the EURO-AV2 socket and the EURO-
AV1 socket.
The sets are interconnected by the switching ICs (IC7550 / IC7552). A
HIGH level is present in this case at the control line MON and LOW
level at the control line DEC.
2.3.3 VPS Programme Scanning
The keyboard control computer takes up a scanning mode if two and
more VPS transmissions have been preprogrammed. For this, the
computer tunes the tuner at certain intervals and for a short time to the
respective TV stations. The IC7540 reads out the current VPS data and
transfers it on the I
2
C-Bus to the keyboard control computer. It is
therefore ensured that the computer detects also transmissions for
which the TV stations have fixed an earlier broadcasting time than
originally planned, and that the video recorder is controlled accord-
ingly.
the dropout compensation switch (DO). On another path, the signal is
fed through a limiting stage (DOUBLE LIM), a FM-demodulator, a
lowpass filter (SUB LPF), a deemphasis stage (MAIN DEEMPH)
containing a playback amplitude control, and an R/P-switch to pin 4 of
the IC7051. Afterwards, the CVS signal is passed through an amplifier
stage (T7007) and C2027 to IC7051-(5). In IC7051, the signal is
clamped (CLAMP) before and after the R/P-switch. After the lowpass
filter (Y-LPF) which follows the signal path divides. In one path, the
luminance signal is fed through a dropout switch and, after an R/P-
switch, leaves the IC7051 on pin 20. In the following delay circuit
(IC7060) the signal is delayed by one line and is then taken via
IC7051-(18) and the following amplifier stage (VCA) to the dropout
switch. If dropouts occur in the signal, the dropout switch changes over
replacing the faulty signal by the faultless delayed signal. In the other
path, the non-delayed and delayed CVS signals are subtracted in a
difference amplifier. The resulting low-frequency noise voltage is
added at opposite phase to the non-delayed Y-signal via a weighting
network. The noise-reduced Y-signal passes through the non-linear
deemphasis (NL DE EMPHASIS), the noise reduction stage (WHI NOI
CAN) for high-frequency noise voltages and a high-frequency preem-
phasis (PICTURE CONTROL). In the following "Y/C-MIX" stage the Y-
signal is added to the internally fed in chroma signal. The regenerated
CCVS signal is passed through an R/P-switch, the V-pulse insertion
stage (QH/QV INS, CHARA INS), a video amplifier (VIDEO AMP) and
is fed out from pin 16 of the IC7051. Subsequently, the CCVS signal
(VSB) is taken via the amplifier stage T7004 and the "OSD" circuit
stage to the "IN/OUT" circuit stage.
2.4.2 Family Board – Chroma
Function Overview
On record the 4.43MHz chroma signal is converted to 627kHz with the
aid of a mixing frequency of 5.06MHz.
On playback the 627kHz chroma signal is reconverted into the original
4.43MHz chroma signal with the aid of the mixing frequency (5.06MHz).
The signal is amplified, added to the luminance signal and passed on
to the modulator or the EURO-AV1 socket.
Record
On record the signal path is the same for PAL and MESECAM (Secam
East). The CCVS signal (VREC) is supplied from the "IN/OUT" circuit
stage to the IC7051 via pin 12. In this IC, the signal passes through the
Video-AGC-circuit, a -6dB-attenuator (1/2), an R/P-switch and an
integrated bandpass (FSC BPF). Here, the chroma signal is separated
from the CCVS signal. The chroma signal is then taken via two R/P-
switches, a gain controlled amplifier (ACC AMP) and a burst emphasis
stage (not active) to the main converter (MAIN CONV). In the main
converter, the chroma signal (4.43MHz) is mixed with the subcarrier
frequency (5.06MHz). In an internal lowpass filter unwanted mixing
products are eliminated from the converted chroma signal (627kHz).
Having passed the R/P-switch, the chroma lowpass filter (C-LPF) and
the colour killer which follow the signal arrives at pin 38 of IC7051. It is
then fed through R3035 or an adjustment control for the chroma
recording current, R3038 (PAL Curr.) to the junction R3035 / R3038 /
R3039 where the signal is added to the Y-signal. The sum signal
(FMRV) is taken to the head amplifier.
Playback
Via the head amplifier, the signal from the tape (FMPV) arrives at
IC7051-(38) in the chroma circuit stage. The signal is then fed through
two R/P switches to the chroma lowpass filter where the 627kHz
chroma signal is selected. Subsequently, the 627kHz chroma signal
passes through a 6dB amplifier, a gain controlled amplifier (ACC
AMP), and arrives via a burst emphasis stage (not active) at the main
converter (MAIN CONV) where it is mixed with the subcarrier fre-
quency (5.06MHz). The reconverted chroma signal (4.43MHz) is fed
through an R/P-switch to the integrated chroma bandpass (FSC BPF).
On one path, the signal is then taken via IC7051-(24) and IC7060-(2)
directly to the comb filter in IC7060. On another path, it is additionally
inverted for PAL/NTSC and passed on via the MESECAM switch,
IC7051-(23) and IC7060-(4), to the comb filter in IC7060.
The function of the comb filter is to delay the inverted signal from
IC7060-(4) by 2 lines periods for the PAL system (by one line for NTSC)
and to add it to the direct signal coming from IC7060-(2). These two
paths form the so-called "comb filter" for crosstalk compensation. On
MESECAM mode, only the direct signal is taken to the comb filter.
Consequently, there is no other signal available for the comb filter to
add so that it is out of operation. At pin 23, the comb filter IC7060 feeds
out the chroma signal and passes it on via pin 26 to IC7051. In this IC,
