Family Board - In/Out, Vps (Io) - Grundig GV 6400 HiFi Service Anleitung

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 µC 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) within the erase oscillator circuit stage (AL) 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 (HA).
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, software/
adjustment values,station tuning data/channels). The data is trans-
2
ferred via the I 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 F1720, 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 T7721.
2 - 10
The demodulated IF signal for FM sound processing is fed out from
IC7720-(13). Via the IF filter F1745 and IC7720-(11), the signal is fed
in for FM demodulation. On IC7720-(9) the AF signal "ALR" is present
which is fed through the "IN/OUT" circuit stage to the Audio stage.
Signal Processing with IC7723
In IC7723, 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 IC7723-(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 IC7723-(16) to the tuner (contact 5). The
control threshold level is adjustable with R3742 (AGC). Between pin
18 and pin 19 of the IC7723, 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 (4A). Finally, the signal is amplified and fed
through IC7723-(8) and the amplifier T7721 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 IC7723-(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
IC7723-(17) for FM demodulation.
In models without the surface acoustic wave filter F1719, pin 28 of
IC7723 is connected to chassis via R4772 so that the IF signal from
the video signal processing stage is also fed out from IC7723-(17).
After the IF filter F1746 or F1747 and IC7723-(15/14), the signal is
routed to the FM demodulators (FM DETECT PLL). The resulting
demodulated "ALR" and "A2R" signals are then taken via
IC7723-(10/11) 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 IC7552 is necessary.
Record, EE and Playback Modes
The audio signals are selected and distributed within the audio circuit
stage, the video signals in switching stage IC7552. This switching IC
is supplied with the input signals from the sources (EURO-AV1,
EURO-AV2, HF, EE/PB/OSD, CV). The signals are selected accord-
ing to the operating mode and fed to the circuit section Video/Chroma
"VREC", or to the output sockets EURO-AV1 "AOUT1" and EURO-
AV2 "AOUT2".
The switches are controlled by the keyboard control computer via the
2
I C bus (SCL / SDA).
On loop-through (EE) and playback mode, the video signal (VSB)
reaches the tuner/modulator 1701 within the frontend stage (FV) on an
indirect path via the OSD circuit stage (VIDOUT) and T7500.
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
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
GV 6400 ..., GV 6401 NIC
GRUNDIG Service