Grundig TVR 3735 FR/TOP Servicehandbuch Seite 33

TVR 3735..., TVR 3740..., TVR 5540...
The generated R/G/B signals pass through the R/G/B selection switch
(SW) and the output stage (Output). The brightness, contrast and
colour saturation can be adjusted via the I
control is additionally provided via pin 22, D502 and the ABL voltage
if the beam current rises to too high a level.
Subsequently, the R/G/B signals leave the I501-(21 / 20 / 19) and arrive
at the picture tube panel via the connector PA901 where they are
amplified within the output ICs I903, I902 and I901 to obtain the DC
level required for the individual picture tube. The black level and white
level are adjusted by the software.
2.3.3 Audio Signal Processing
The audio signal selected in the integrated selection switch with
volume control of I501 is fed out from I501-(15) and is supplied to the
output stage I601-(1 / 9). This IC works to the principle of a bridge
amplifier and is provided with a thermal overload protection stage.
2.3.4 Horizontal and Vertical Synchronisation
The CCVS signal selected by the input selection switch of the video
signal processing stage (CVBS+SW) is fed through the trap and
passed on to the sync separator where the horizontal and vertical
synchronising signals are filtered off. The horizontal synchronising
signal is passed on to the "Phase 1" controlling stage (PHI-1) and the
vertical synchronising signal starts up the line counter (H/V DIV) for
vertical synchronisation.
The Phase 1 control is a control of frequency of the line oscillator
(VCO+Control). The time constant of the control loop is determined by
the components connected to I501-(43). The following Phase 2 control
(PHI-2) sets a phase 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 I501-(41)
for evaluation. The resulting control voltage is smoothed by CC536 at
I501-(42). The horizontal pulses (HD) are passed through I501-(40)
and plug contact PA406-(3) to the horizontal output stage on the Power
Chassis.
After counting up to 312 line pulses, the line counter (H/V DIV) feeds out
a vertical synchronising pulse if no CCVS signal is available for synchro-
nisation. This pulse triggers the saw-tooth generator of the vertical
output stage (VERT GEOM.) of I501 which works to the principle of a
constant current source. For this, the capacitor C546 is connected to
I501-(51). The vertical deflection voltages leave the I501 from Pins 46 /
47 and pass on via plug contacts PA405-(3 / 2) to the vertical output
stage on the Power Chassis.
2.4 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.
Coming in from contact 1 of the tuner U102, the IF signal passes
through the surface acoustic wave filter SF03, which determines the IF
bandpass. Via I201-(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 I201-(12) to the tuner U102-(8). The control
threshold level is adjustable with R202 (SUB AGC). Between Pin 13
and Pin 14 of the I201, the demodulated IF signal passes through a
sound trap Z206 / Z207, in which the audio component of the CCVS
signal is suppressed. Subsequently, the signal is amplified and fed
from I201-(7) and the amplifier stage QC102 to the output selection
switch I504-(3) and the Video/Chroma circuit IY01-(30).
GRUNDIG Service
C bus. Automatic contrast
2
The demodulated IF signal for FM sound processing is fed out from
I201-(13). Via the IF filter Z204 / Z209 and I201-(11), the signal is fed
in for FM demodulation. On I201-(9) the AF signal is present and,
following the deemphasis circuit RC204 / CC202, it is passed through
the amplifier stage QC205, the sound standards switch IL02 (optional)
and the amplifier stage QCL06. It arrives at the output selection switch
I504-(1) and the Standard Sound circuit stage IY01-(73).
The IF signal for AM audio signal processing (SECAM-L) is fed from
contact 1 of the tuner U102 through the amplifier stage QC201 to the
surface acoustic wave filter SF04. 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 SF04 are released by the switching voltage "SECAM-L'2"
via QC203 / QC202. This voltage is at HIGH level in Band I of the
SECAM-L standard. The filtered IF signal is then taken to IL02-(1 / 14).
In IL02, the signal is passed to a gain controlled amplifier and an AM
demodulator. It leaves on IL02-(9) and is taken via the amplifier QCL06
to the output selection switch I504-(1) and to the Standard Sound
circuit stage IY01-(73).
2.5 Signal Chassis – VCR Signal Electronic (VS)
2.5.1 Signal Chassis – 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 TV Signal Electronics circuit stage
I501-(17).
Record Signal Path
The CCVS signal from Frontend 2 is fed from pin 30 of IY01 through
a clamping stage (CLAMP) and the input selection switch to
IY01-(34 / 35). From there, it is passed through the Video-AGC-stage,
an R/P-switch, a -6dB attenuator (1/2), another R/P switch, a lowpass
filter (LPF) for suppressing the chroma component of the CCVS signal,
and a few stages which are not active on record mode. After the R/P-
switch the signal is fed out from the IY01 on 25. The CVS signal is fed
via an emitter follower QCY03 to IY01-(26). In this IC, the signal is
subjected to a clamping stage, a DETAIL ENHANCER and the NLE-
stage (non-linear emphasis). 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 to
achieve a better signal-to-noise ratio. The peripheral circuit for the
linear pre-emphasis consists of CCY48 (at pin 24). The luminance
signal is then fed to the FM Modulator in IY01.
The frequency-modulated signal leaves IY01 on Pin 18 and is taken via
IY04-(9) to the AGC stage of the head amplifier where it is added to the
chroma signal. The sum signal is passed through the record amplifier
stage (CURRENT AMP), the REC/PB switch, Pin 17 of IY04 and plug
contact PAY01-(6) to the headwheel.
Playback
On playback, the signal from the tape (FMPV) passes through the head
amplifier IY04-(16 / 19 / 7) where it is amplified and the signals from the
active heads are combined, to a few matching circuits for correction of
the frequency response and the delay time (QCY08 / QCN02). Subse-
quently, the signal is fed through the emitter follower QCY11 to Pin 1
of the IY01.
In IY01, the FM signal passes through the stages S-EQ / PB-EQ for
frequency response linearisation and QCY07 located between Pin 17
and Pin 18. Variations in the signal level are compensated for in the
FM-AGC stage. Dropouts are compensated for by the dropout com-
pensation circuit within the Y-NR stage. The signal is then fed through
a limiting stage (DOUBLE LIMIT), a FM-demodulator, a lowpass filter
(SUB LPF), and an R/P-switch to Pin 25. Following the external
Description
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