GRUNDIG Service
2 - 9
k
GV 26 EURO, GV 6000 EURO, GV 6300 EURO
Descriptions
2.1.6 Tape Servo Control
The capstan motor is a three-phase motor which is fitted with Hall
generators. These generate signals which are fed to the capstan motor
driver IC (LB1897) in the capstan motor assembly. Depending upon
these signals the IC commutates the individual phases of the capstan
motor.
The sense of rotation (CREV) is switched over via IC7400-(5) (LOW
level for the forward sense of rotation or a HIGH level for the reverse
direction).
This control signal is passed through plug contact 1946-(2)
to the capstan motor driver. For speed control, the FG Hall element
(Magneto Recitive Element) in the capstan motor generates pulses at
a frequency of 1514Hz at the rated speed. The pulses (FG) from the
capstan motor driver IC (LB1897)
for speed control are fed via plug
contact 1946-(4) and the comparator in IC7460-(8/11) to IC7400-(13).
The tachopulses (actual value) are compared in the IC7400 with an
internally generated reference value. From IC7400-(25) the
µ
C feeds
out a pulse-width-modulated square wave voltage (CAP). This is
integrated by R3482 / C2461 and fed via plug contact 1946-(6) as a
control voltage to the capstan motor driver IC (LB1897).
For the functions "Wind/Rewind" and "Picture Search Forward/Back-
ward" (
≥
3) in VCR models with High Speed Drive the supply for the
capstan motor driver is switched over from +8.8V to +14.6V. This is
done by the control signal (CSW) from the deck computer IC7400-(59)
via plug contact 1942-(8) within the power supply unit.
2.1.7 Tracking / Autotracking
During recording, encoded 25Hz-CTL-pulses are recorded onto the
tape via the sync head. These pulses are required on playback for
tracking control.
On recording, the 25Hz pulses are taken from IC7400-(16) to
IC7460-(16) and are then passed through IC7460-(2) and the connec-
tor 1961-(7) to the sync head.
On playback, the recorded CTL pulses are scanned by the sync head
to be subsequently converted to square wave pulses in IC7460 and
passed on via IC7460-(16) to IC7400-(11/14).
When a cassette is loaded, the Autotracking function determines the
optimum track position on playing back. For this, a voltage "TRIV"
(Tracking Information Video) is derived from the envelope of the FM
packages and fed in to the main computer IC7400 on the analog input
(pin 50). This voltage is generated in the head amplifier (HV).
On the basis of the tracking centre position, the nominal tracking value
is increased or reduced. For each of the two directions, the appropriate
nominal value is determined at which the voltage derived from the FM
envelope "TRIV" starts to decrease as against the maximum determi-
ned voltage level. The mid-value between the two limit values is then
used as the optimum tracking value. On completion of this meas-
urement, the Autotracking function is switched off and the determined
phase is controlled by the CTL pulses.
If more than two successive CTL pulses are missing, the Autotracking
function is reactivated assuming, in this case, that a new recording with
a different tracking position is played back.
2.1.8 EEPROM
In the EEPROM (IC7890) the control computer (IC7201) stores special
data of the customer and the machine (eg. option code, station tuning
data/channels, software/adjustment values). The data is transferred
via the I
2
C-bus (SDA / SCL).
2.2 Family Board – Frontend (FV)
The Frontend has the function of amplifying and demodulating the IF
signal fed in from the tuner. The resulting signals are the CCVS signal
and the audio signal.
Signal Processing with IC7720
Coming from the tuner contact 1701-(17), the IF signal passes through
the surface acoustic wave filter F1721, which determines the IF band
pass. Via IC7720-(1/2), the signal is fed to a gain controlled wideband
amplifier with synchronous demodulator, and subsequently, to a video
amplifier. Another stage in the IC is used to generate the control
voltage for the wideband amplifier and the tuner. This control voltage
is fed from IC7720-(12) to the tuner (contact 5). The control threshold
level is adjustable with R3742 (AGC). Between pin 13 and pin 14 of the
IC7720, the demodulated IF signal passes through a sound trap
F1740, in which the audio component of the CCVS signal is sup-
pressed. Subsequently, the signal is amplified and passed on to the
"IN/OUT" circuit stage (as a "VFV"-signal) via IC7720-(7) and the
amplifier T7725.
The demodulated IF signal for FM sound processing is fed out from
IC7720-(13). Via the IF filter F1745 or F1746 and IC7720-(11), the
signal is fed in for FM demodulation. On IC7720-(9) the AF signal "AFV"
is present and, following the deemphasis circuit R3737 / C2276 and
the amplifier T7723, it is fed via the "IN/OUT" circuit stage to the Sound
stage.
Signal Processing with IC7721
In IC7721, the video and audio signals are separately processed and
demodulated.
– Video signal processing
From tuner contact 1701-(17), the IF signal passes through the
surface acoustic wave filter F1721, which determines the IF band
pass. Via IC7721-(1/2), the signal is fed to a gain controlled wide-
band amplifier with synchronous demodulator, and subsequently, to
a video amplifier. Another stage in the IC is used to generate the
control voltage for the wideband amplifier and the tuner. This control
voltage is fed through IC7721-(16) to the tuner (contact 5). The
control threshold level is adjustable with R3742 (AGC). Between pin
18 and pin 19 of the IC7721, the demodulated IF signal passes
through a sound trap F1740, in which the audio component of the
CCVS signal is suppressed. This is not necessary for the SECAM-
DK and SECAM-L standards. In this case, the sound trap 1740 is
bridged by IC7722-(11…14). Finally, the signal is amplified and fed
through IC7721-(8) and the amplifier T7725 to the "IN/OUT" circuit
stage (as a "VFV" signal).
– Audio signal processing
From the tuner contact 1701-(17), the IF signal passes through the
surface acoustic wave filter F1719, which determines the IF band
pass. Via IC7721-(27/28), the signal is fed to a gain controlled
wideband amplifier with synchronous demodulator. On one path,
the demodulated IF signal is directly fed through the AM demodula-
tor to the output amplifier. On another path, the signal is fed out from
IC7721-(17) for FM demodulation. After the IF filter F1745 or F1746
and IC7721-(15), the signal is passed through the FM demodulator
(FM-PLL) to the output amplifier. As "AFV", the signal is taken via
IC7721-(10) to the "IN/OUT" circuit stage.
2.3 Family Board – IN/OUT, VPS (IO)
General
The universal applicability of these video recorders requires special
facilities for distributing the input and output signals corresponding to
the operating mode. For this, the switching ICs IC7550, IC7551 and
IC7552 are necessary.
2.3.1 Record, EE and Playback Modes
The signals are selected and distributed in the switching ICs. In video
recorders fitted with one EURO-AV socket, it is IC7551 for video and
audio signals. In models fitted with two EURO-AV sockets, these
switching ICs are IC7552 for the video signals, and IC7551/IC7550 for
the audio signals. These switching ICs are supplied with the input
signals from the sources (EURO-AV1, EURO-AV2, LINE-Front, CV,
RF, EE/PB/OSD). The signals are selected according to the operating
mode and fed to the circuit sections Video/Chroma "VREC" and
Standard Sound "AMLR", and the output sockets EURO-AV1 "AOUT1"
and EURO-AV2 "AOUT2" respectively.
The switches are controlled by the keyboard control computer via the
I
2
C bus (SCL / SDA) and the control line IS2. The control line IS1 is
driven via the tape deck computer.
On loop-through (EE) and playback mode, the audio signal (AMLP) is
directly passed on to the modulator 1701 in the Frontend, the video
signal (VIDOUT) reaches the modulator on an indirect path via the
OSD circuit stage (VOSD) and T7500.
2.3.2 Decoder Operation
For financial and copyright reasons, a couple of private television
stations transmit scrambled video and audio signals so that a Pay-TV-
Decoder is required to descramble the signals.
– Technical realization
The Pay-TV-Decoder is connected to the EURO-AV2 socket and the
TV receiver to the EURO-AV1 socket.
This connection makes it possible to operate the Pay-TV-Decoder in
combination with the TV receiver and also with the video recorder
without changing the connections.
When using the video recorder, the coded video and audio signals are
taken via the EURO-AV2 socket to the Pay-TV-Decoder. The Decoder
descrambles the signals and feeds them back to the video recorder.
This signal path must be released for the individual programmes when
