k
2 - 12
GRUNDIG Service
Descriptions
TVR 3710 …, TVR 5100 …,TVR 5500 …
level for the forward sense of rotation or a HIGH level for the reverse
direction. This control signal is passed through plug contact 1905-(4)
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) pin 3 for speed control are fed via
plug contact 1905-(2), IC7411-(8), to the internal comparator and
IC7411-(11) to IC7410-(19). The tachopulses (actual value) are com-
pared in the IC7410 with an internally generated reference value. From
IC7410-(31) the
µ
C feeds out a pulse-width-modulated square wave
voltage (CAP). This is integrated by R3476 / C2471 and fed via plug
contact 1905-(3) as a control voltage to the capstan motor driver IC
(LB1897).
For the functions "Wind/Rewind" and "Picture Search Forward/Back-
ward" (
≥
3) the supply for the capstan motor driver is switched over from
+8.8V to +14.6V. This is done by the control signal (IWIND) from the
deck computer IC7410-(51) and the transistor stage T7493 / T7492 /
T7491.
3.1.7 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 IC7410-(22) to
IC7411-(16) and are then passed through IC7411-(2) and the connec-
tor 1901-(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 IC7411 and
passed on via IC7411-(16) to IC7410-(17/20).
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 IC7410 on the analog input
(pin 59). This voltage is generated in the head amplifier.
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.
– Chroma standards switching (optional) for tuner 1 is effected via:
Pin 5 (PSS) – PAL / SECAM
Pin 11 (MES) – MESECAM / SECAM-L
Pin 63 (SB1_1) – SECAM-L - Band I / III / UHF
For tuner 2 (optional) the switching of chroma standards is effected via:
Pin 3 (PSS2) – PAL / SECAM
Pin 6 (MNT2) – MESECAM / SECAM-L
Pin 54 (SB1_2) – SECAM-L - Band I / III / UHF
– For monitoring the EHT, the control voltage "PROT" is applied via
pin 53 to the keyboard control computer. If there is a fault in the EHT
stage, the voltage level is <1.5V and the EHT generation is stopped
by the switching voltage "MONI" on pin 61 (LOW).
– For on-screen-display of information the keyboard control com-
puter feeds out the blanking signals (pin 33 - RED; pin 34 - GREEN;
pin 35 - BLUE, and pin 36 BLANKING). The oscillator circuit for the
internal column counter is located between pin 42 and pin 43. For
synchronising the inserted display, for determining the position of
the appropriate pixels on the screen, the horizontal and vertical
synchronising pulses are fed through pins 37 and 38 to the character
generator within the keyboard control computer. These synchronis-
ing pulses are generated from the Super Sandcastle pulses (HFB/
SC) by the comparators in IC7870.
– The drifting of tuner 1 or of the aerial signal produces the AFC1
control voltage in the Frontend circuit of the TV-Signalelectronic.
This voltage is supplied to pin 24 and the keyboard control computer
readjusts the tuner tuning voltage via the I
2
C bus.
– In the case of power failure the capacitor C2802 provides the
supply for the clock and the RAM at Pin 64. The diode D6801
prevents the capacitor from discharging. During the time of the
power failure, a LOW level exists at Pin 48 so that further functions
of the IC are switched off by the system quartz Q1801 at pins 45 / 46.
– In the EEPROM (IC7813) the control computer (IC7801) 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).
– VPS/PDC 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 IC7840 reads out the current VPS
data and transfers it on the I
2
C-bus to the keyboard control compu-
ter. It is therefore ensured that the computer detects also transmis-
sions for which the TV stations have fixed an earlier broadcasting
time than originally planned, and that the video recorder is controlled
accordingly.
3.2 Signal Chassis – Keyboard Control Unit (CO)
The microcomputer IC7801 is the heart of the keyboard control unit and
takes over the following functions together with the corresponding
function groups:
– Evaluation of the keyboard matrix.
– Decoding of the remote control commands from the infra-red
receiver IC7812.
– Quartz clock
– Integrated RAM for storing the timer data
– Driving the light emitting diodes (Timer / Record / Standby) via
pins 28 / 29 / 31
– Bidirectional serial interface (DATD1 - pin 7, DATD2 - pin 8 and
CLKD1 - pin 9) for data communication between the keyboard
control computer and the deck computer.
– I
2
C-bus (SDA - pin 56, SCL - pin 55) connecting the following
function groups with each other:
EEPROM – IC7813
Tuner 1 – 1701 or 1702
Tuner 2 – 1301
VPS/PDC – IC7840
Teletext – IC7881 or IC7880 (Teletext / VPS / PDC)
– Analog outputs controlling the following settings via:
pin 18 (VOL) – volume level
pin 14 (BRI) – brightness
pin 17 (CONTR) – contrast
pin 15 (SHP/COIN) – picture sharpness
pin 19 (SAT) – colour saturation
pin 16 (HUE) – hue (TINT for NTSC)
3.3 Signal Chassis – TV Signal Electronics (TV)
The TV Signal Electronics consists essentially of the following function
groups, most of which are integrated in IC7200:
– Frontend
– Video signal processing
– Audio signal processing
– Horizontal and vertical synchronisation
3.3.1 Frontend
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.
Coming from the tuner contact 1701-(17) or 1702-(17), the IF signal
passes through the surface acoustic wave filter F1720, which de-
termines the IF band pass. Via IC7200-(45/46), the signal is fed to a
gain controlled wideband amplifier with synchronous demodulator,
and subsequently, to a video amplifier. Another stage in this IC is used
to generate the control voltage for the wideband amplifier and the
tuner. This control voltage is fed from IC7200-(47) to the tuner
(contact 5). The control threshold level is adjustable with R3712
(AGC1). The demodulated IF signal is fed out from pin 7 of IC7200.
After the amplifier stage T7762 the signal path divides.
– For video signal processing, the demodulated IF signal passes
through the sound trap F1740, in which the audio component of the
CCVS signal is attenuated. For the SECAM DK and L television
standards, the signal does not need to be subjected to the sound trap
1740 which is bridged by IC7705-(3…5 / 9) for this purpose. Subse-
quently, the signal is fed through the impedance converter T7216
and IC7200-(13) to the input selection switch of the video signal
processing stage (Luminance Switch). Additionally, the signal is
passed to the "IN/OUT" circuit stage via T7215 as the "VFV1"-signal.
