Small Signal - Matsui 1410R Service Manual

Small signal

IC 7015 (TDA836X) is a single-chip video processor with built in IF- detector, luminance and chrominance separator, PAL chroma
decoder, RGB processing , horitzontal&vertical syn. processor, FM sound- decoder,
IF (INTERMEDIATE FRECUENCY) DEMODULATION (ic7015/6A)
IC 7015/6A contains the IF detector. The 38.9 MHz IF signal is a present at the output pin 11 of the tuner (33.4 MHz for a sign al
according to the SECAM L' system).
Bandpass filter; The IF bandpass characteristic is determinated by the bandpass of the SAW (Surface Acoustic Wave) filter 1015.
* For PAL BG sets a SAW filter with 5.5 MHz bandwich is used (33.4 to 38.9 MHz).
* For PAL I sets a SAW filter with a bandwinch of 6.0 MHz is used (33.4 to 39.4 MHz).
* For PAL BGI/SECAM BGLL' sets a SAW filter with 6.0 MHz bandwich is used to enable BGILL' reception.
* For LL' reception BG/L is "high", D6014 conducts and so the 33.4 MHz is tuned to a lower frecuency with C2014 (32.9 to 38.9 M Hz).
* For BGIDK reception BG/L is "low", D6014 does no conduct. With C2013 the bandpass filter is tuned at 33.4 MHz (32.4 to 38.9
MHz).
* For PAL BG/SECAM BGDK sets a SAW filter with a bandwich of 6.5 MHz is used without switching possibilities (32.4 to 38.9
MHz).
Demodulation and AGC; After the bandpass filter the IF signal is supplied to the IF-detector IC7015/6A pins 45 and 46. This IC7015
6A is suitable for a both negative (BGIDK) and positive (LL') modulation controlled by the BG/L switching signal (" high" for LL' positive
modulation, "low" for a BGDIK negative modulation) at pin 1 IC7015/6F (pin 1 IC7015/6F is at DC level input pin for positive/negative
switching of IC7015/6A). This control also determinates whether the AGC circuit controls at the top white level (positive modulation) or
at the top sync level (negative modulation).
The high-frecuency AGC voltage is available at pin 47. The take over level of the high-frecuency (delayed) AGC control can be set at
pin 49 by means of R3021. For switching to diferent IF for the SECAM L' system (33.4 MHz) the demodulation reference circuit 5040
at pins 2 and 3 IC7015/6A is switched by switching signal L/L'.
* For BGILDK reception L/L' is "low", D6042 conduct and so coil 5043 is connected in parallel to 5040. The circuit is tuned to 38.9
MHz.
* For reception L/L' is "high", D6042 does nor conduct. The circuit is tuned to 33.4 Mhz by L5040 only.
Note: For sets with LL' reception L5040 is tuned at 33.4 MHz, for sets without LL' reception L5040 is tuned at 38.9 MHz (or 39.5
MHz for PAL I only sets).
Automatic Frecuency Control (AFC) signal at pin 44 is obtained from the reference signal of the IF-detector and the control is
modified internally in IC7015/6A for positive or negative modulation. C2037 smoothes the AFC voltage.
SOURCE SELECT, LUMINANCE AND CHROMINANCE SEPARATION (IC7015/6B)
Sound trap; The baseband CVBS signal of pin 7 IC7015/6A (nominal amplitude of 2Vpp) also contains the 5.5 or 6.0 MHz FM sound
signal (FM intercarrier sound). This sound signal is filtered out with a 5.5 MHz (6.0 MHz PAL I) ceramic filter (1032 and/or 10 33).
Source select: The CVBS signal is now fed to pin 13 IC7015/6B to the source selector switch in IC7015/6B. Pin INT/EXT = 0V gives
internal CVBS (pin 13), pin 16 INT/EXT = 8V gives external CVBS (pin 15) (external signal SCART CVBS IN from the CVBS IN cinch
or pin 20 scart-connector).
Luminance and chrominance separation: chrominance signal is filtered out (-20dB) by a luminance notch filter which is internallly
calibrated at the subcarrier frecuency (4.43 or 3.58). The IDENT status signal is coming from pin 14 IC7015/6B. In case of no
horizontal sync (so no signal detected) by the sync processor IC7015/6E, pin 14 IC7015/6B is made "low", TS7651 does not conduc t
so pin 16 of the µC is "high". The IDENT signal is internally fed to ensuring stable OSD even without transmiter signal (IC7015/6D can
be switched to different time constants).
CHROMINANCE DECODING (IC7015/6C)
CVBS is extracted from the baseband CVBS signal from the IF-detector via crystals 1032. PAL (and NTSC if applicable) chroma
decoding inside IC7015/6C, SECAM chroma decoding inside IC7250.
Inside IC7015/6C the PAL (or NTSC) chroma signal is fed via amplification and a burst demodulator to the R-Y and B-Y demodulator.
(PAL or NTSC processing is determined automatically by the burst demodulator inside IC7015/6C). The 4.43 MHz reference crysta l
for chrominance demodulation in IC7015/6Cis in present at pin 35 of IC7015/6C.
Pin 27 shoud be 5V5 (via R3280) to force IC7015 in the PAL/SECAM mode; by then IC7015/6C is in the PAL decoding mode and via
pin 27 feeds throught the chroma signal to the SECAM chroma decoder IC7250 (so IC7015/6C searches for PAL and IC7250
searches for SECAM).
Via a bidirectional communication line between pin 32 of IC7015/6C and pin of IC7250 both IC7015/6C and IC7250 "know" wether
a PAL or a SECAM signal is detected:
- On AC level there is a 4,43 calibration for calibration of thr PLL and chroma cloche filter of IC7250.
- On DC level there is a SECAM or PAL switching line enabling automatic selection of IC7015/6C and IC7250 to supply R-Y and B-
Y to the delay line IC7271.
* If IC7015/6C has detected a PAL signal, Vpin 32 is made 1V5. By then the demodulated R-Y and B-Y at output pins 30 and 31 od
IC7015 / 6C are fed to delay line IC7271.
* If IC7015/6C has detected a PAL signal, Vpin 32 is made 5V. By then the demodulated R-Y and B-Y at output pins 30 and 31 of
IC7015/6C are not fed to the delay line IC7271.
* If IC7250 has detected SECAM Vpin 1 IC7250 becomes "low", sinking typical 150 µA from the 5V from pin 32 IC7015/6C. Only in
case the sinking current at pin 32 IC7015/6C is typical 150 µA, only by then IC7015/6C "knows" IC7250 has detected SECAM
demodulated R-Y and B-Y are fed to the delay line IC7271 via output pins 9 and 10 of IC7250.
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