Circuit Descriptions - Matsui 1410R Service Manual

CIRCUIT DESCRIPTION
1.- SMALL SIGNAL PROCESSING (Diagram A)
The small signal is processed by TDA8361, (TDA8360 no scart) for Pal sets and TDA8362 for Pal/Secam
sets (IC 7015), including IF detection, video processing, chroma decoder, RGB processing, sync processor
and FM sound decoder.
1.1- IF detection (IC7015/6A)
- IF input (pins 45,46): The IF signal comes from pin 11 of the tuner to the IF SAW (Surface Acoustic Wave)
filter (1015) and the IF-detector IC7015/6A (pins 45 and 46).
- IF filter (1015): The IF bandpass characteristic, determined by the SAW filter, is 33.4 to 38.9 MHz. for BG
sets, 33.5 to 39.5 MHz. for PAL I sets and 32.4 to 38.9 MHz. for DK sets.
- IF oscillator (pins 2,3): Carrier frequency, present in coil L5040, is tuned at 38.9 MHz. for BG sets or
39.5 MHz for Pal I sets
- AGC voltage (pin 47): The AGC delayed voltage is applied to pin 1 of the tuner. It should be adjusted
for 1mV. antenna signal by means of R3021 (pin 49).
- AFC signal (pin 44): The Automatic Frequency Control is obtained from the reference signal of the IF-
detector. C2037 smoothes the AFC voltage.
- Identification (pin 4): The identification output is applied to pin 16 of the µC. This signal is high in case of
signal detected.
- Video output (pin 7) : This baseband CVBS signal with 2Vpp of nominal amplitude, also contains the FM
intercarrier sound signal. Sound is filtered out by a ceramic trap (1032 or 1033) which frequency can be
different depending on the system: 5.5 MHz. for BGLL', 6.0 MHz. Pal I or 6,5 MHz. for DK.
Multistandard sets
-The IC TDA8362 changes automatically between negative (BGIDK) and positive (LL') modulation.
The IC also determines if the AGC circuit should control at the top white level of the video (positive
modulation) or at the top sync level (negative modulation).
-Saw filter (1015) bandpass characteristic is modified by BG/L switching signal proceeding from the
microcontroller:
- For BGIDK reception BG/L is low, D6014 does no conduct and the bandpass filter is tuned by
5012 and 2013 at 32.9MHz. to 38,9 MHz.
- For LL' reception BG/L is high, D6014 conducts and so the bandpass filter is tuned by 5012 and
C2014 at 32.4 to 38.9 MHz.
-Oscillator frequency is controlled by the L/L' switching signal:
-For BGIL 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 L' reception L/L ' is high, D6042 does nor conduct and the circuit is tuned to 33.4 MHz. by L5040 only.
1.2- Source select, luminance and chroma separation (IC7015/6B)
- Source select (pin 13, 15, 16): The internal CVBS signal is now fed to pin 13 IC7015/6B. External CVBS
from the pin 20 of Euroconnector is present on pin 15. The source selector switch between internal (pin 16 = 0V.)
or external (pin 16 = 8V.).
- Luminance and chrominance separation: Chrominance signal is filtered out (-20dB) by a luminance
notch filter which is internally calibrated at the subcarrier frequency (4.43MHz).
1.3- Chroma Decoding (IC7015/6C)
Pal or Secam signals are recognized automatically by the IC. For Pal signals decoding is made in IC7015/
6C and for Secam signals in IC7250 (TDA8395).
- Pal signal: This signal is amplified and demodulated. The 4.43 MHz. reference crystal for chrominance
demodulation is present at pin 35 of IC7015/6C. The R-Y and B-Y out-puts (pins 30, 31) are applied to
chroma delay line IC7221 (TDA4665).
- Secam signal (pin 27): This signal is applied to pin 16 of Secam decoder IC7250.
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