GRUNDIG Service
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TVR 3710 …, TVR 5100 …,TVR 5500 …
Descriptions
reference between the horizontal synchronising signal and the actual
position of the electron beam. To establish the position of the beam the
line flyback pulses are fed back to IC7200-(38) for evaluation. The
resulting control voltage is smoothed by C2204 at IC7200-(39). The
horizontal position of the picture is also determined by the preset
R3206 (H-SHIFT) on pin 39. This introduces a DC voltage off-set to
shift the picture. The horizontal pulses (HDR) are passed through
IC7200-(37) and plug contact 1911-(2) to the horizontal output stage
on the Power Chassis.
After counting up to 312 line pulses, the line counter (Vertical Divider)
feeds out a vertical synchronising pulse. This pulse triggers the saw-
tooth generator of the vertical output stage of IC7200 which works to the
principle of a constant current source. For this, the capacitor C2200 is
connected to IC7200-(42). For various settings (vertical linearity, picture
height, and vertical position) the vertical output stage of IC7200 obtains
from the vertical output stage on the Power Chassis the "VFB" feedback
signal via IC7200-(41). The preset controls influencing the "VFB"
feedback signal are located on the Power Chassis. The compensated
deflection saw-tooth leaves the IC7200 from pin 43 and passes on via
plug contact 1922-(5) to the vertical output stage on the Power Chassis.
– The demodulated IF signal for FM audio signal processing is fed via
the IF filter F1745, or optionally via F1746 and IC7705-(11…14), to
IC7200-(5). Subsequently, the filtered sound IF is subjected to the
limiter, the PLL demodulator and is passed on to the preamplifier /
mute circuit. The demodulated audio signal "AFV1" passes through
IC7200-(1) and amplifier T7703 to arrive at the IN/OUT circuit stage.
The IF signal for AM audio signal processing (SECAM-L) is fed from
contact 17 of the tuner 1701 or 1702 to the surface acoustic wave filter
F1750. This filter is provided with an additional input for the vision and
sound carriers in Band I of the SECAM-L standard which are reversed
when compared to the other Bands. The inputs, pin 1 (Band I) and pin
2, of the surface acoustic wave filter F1750 are released by the
switching voltage "SB1_1" via T7707 / T7708. This voltage is at LOW
level on Band I of the SECAM-L standard. The filtered IF signal is then
taken to IC7754-(1/16). In IC7754, the signal is passed to a gain
controlled amplifier and an AM demodulator. Subsequently, it is fed
through IC7754-(7) to a sound standards switch. The "AFV1" audio
signal is fed out from pin 8 and taken to the "IN/OUT" circuit stage.
3.3.2 Video Signal Processing
The input selection switch of the video signal processing stage
(Luminance Switch) receives two CCVS signals for selection, the
signal from the frontend at IC7200-(13) and the external signal "VEXT",
e.g. from the VCR stage, at IC7200-(15). Subsequently, the signal path
in the "trap and bypass" stage divides. One path is to the luminance,
the other path to the chrominance processing stage.
– The trap separates the luminance component (CVS) from the CCVS
signal. The integrated delay line (Y-delay/peaking) compensates for
the time differences between the luminance and the chrominance
signal. The peaking stage improves the sharpness of the edges. The
CVS signal is then taken to the luminance/matrix stage where the
R/G/B signals are generated.
– The chrominance signal is filtered by passing it through the chromi-
nance bandpass. The amplitude of the chrominance signal is
controlled in a control circuit (ACC amplifier) for colour limiting and
colour gain and is then fed to the PAL colour demodulator. For colour
demodulation, the burst is sampled from the chrominance signal in
a phase detector. The burst is used to synchronise the XTal
oscillator. The quartz for the 4.433664MHz oscillator is connected to
pin 35. This colour carrier frequency is used to demodulate the
colour component signals which leave the IC7200 as R-Y (pin 30)
and B-Y (pin 31). The SECAM demodulation (optional) is carried out
in the external IC7202. For this, the chrominance signal is supplied
from IC7200-(27) to IC7202-(16). The colour carrier frequency for
IC7202-(1) is obtained via IC7200-(32) from the XTal oscillator. The
demodulated R-Y and B-Y signals are fed out from IC7202-(10/9).
After the delay line IC7201, the two signals (R-Y / B-Y) are fed into
IC7200-(29/28) for being clamped. Additionally, the colour satura-
tion can be controlled in the clamping stage by the "SAT" control
voltage at IC7200-(26). In the "matrix" stage which follows the R/G/B
signals are generated using the luminance signal.
The generated R/G/B signals pass through the R/G/B selection switch
(Clamp Switch). In the output stage, the R/G/B signals are controlled
in brightness (BRI) via pin 17 and in contrast (CONTR) via pin 25.
Automatic contrast control is additionally provided via pin 25, D6200
and the BCI voltage if the beam current rises to too high a level.
Subsequently, the R/G/B signals leave the IC7200-(20/19/18) and
arrive at the picture tube panel via the connector 1913.
3.3.3 Audio Signal Processing
The audio signal (ATV) selected in the "IN/OUT" circuit stage is fed out
from IC7200-(50) is directly supplied to the audio output stage
IC7240-(3). This IC works to the principle of a bridge amplifier and is
provided with a thermal overload protection stage. The volume setting
is effected by the "VOL" control voltage at IC7240-(5). If the control
voltage is lower than 0.4V, the IC7240 automatically switches to the
mute mode.
3.3.4 Horizontal and Vertical Synchronisation
The CCVS signal selected by the input selection switch of the video
signal processing stage (Luminance Switch) is fed through the trap and
bypass stage to the sync separator (H AND V SEP.). The horizontal
and vertical synchronising signals are filtered off from the Y-signal. The
horizontal synchronising signal is passed on to the Phase 1 controlling
stage and the vertical synchronising signal starts up the line counter
(Vertical Divider) for vertical synchronisation.
The Phase 1 control is a control of frequency of the line oscillator. The
time constant of the control loop is determined by the components
connected to IC7200-(40). The following Phase 2 control sets a phase
3.4 Signal Chassis – Frontend 2 (TU2)
In models fitted with 2 tuners (one for TV, one for video) the Frontend
2 has the function of amplifying and demodulating the IF signal fed in
from the tuner for video recording. The resulting signals are the CCVS
signal and the audio signal.
Signal Processing with IC7300
Coming from the tuner contact 1301-(17), the IF signal passes through
the surface acoustic wave filter F1320, which determines the IF band
pass. Via IC7300-(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 IC7300-(12) to the tuner (contact 5). The control threshold
level is adjustable with R3341 (AGC2). Between pin 13 and pin 14 of
the IC7300, the demodulated IF signal passes through a sound trap
F1340, 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 "VFV2"-signal) via IC7300-(7) and the
amplifier T7310.
The demodulated IF signal for FM sound processing is fed out from
IC7300-(13). Via the IF filter F1345 and IC7300-(11), the signal is fed
in for FM demodulation. On IC7300-(9) the AF signal "AFV2" is present
and, following the deemphasis circuit R3324 / C2319 and the amplifier
T7309, it is fed via the "IN/OUT" circuit stage to the Sound stage.
Signal Processing with IC7301
In IC7301, the video and audio signals are separately processed and
demodulated.
– Video signal processing
From tuner contact 1301-(17), the IF signal passes through the surface
acoustic wave filter F1320, which determines the IF band pass. Via
IC7301-(1/2), the signal is fed to a gain controlled wideband amplifier with
synchronous demodulator, and subsequently, to a video amplifier. An-
other stage in the IC is used to generate the control voltage for the
wideband amplifier and the tuner. This control voltage is fed through
IC7301-(16) to the tuner (contact 5). The control threshold level is
adjustable with R3341 (AGC2). Between pin 18 and pin 19 of the IC7301,
the demodulated IF signal passes through a sound trap F1340, 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 1340 is bridged by IC7312-(11…14). Finally, the signal is
amplified and fed through IC7301-(8) and the amplifier T7310 to the "IN/
OUT" circuit stage (as a "VFV2" signal).
– Audio signal processing
From the tuner contact 1301-(17), the IF signal passes through the
surface acoustic wave filter F1322, which determines the IF band
pass. Via IC7301-(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
IC7301-(17) for FM demodulation. After the IF filter F1345 or F1346,
the selection switch IC7312-(1/2/10/15) and IC7301-(15), the signal
is passed through the FM demodulator (FM-PLL) to the output
amplifier. As "AFV2", the signal is taken via IC7301-(10) to the
"IN/OUT" circuit stage.
