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1. INTRODUCTION:
SAT-507D satellite receiver is designed to work for years under proper conditions without
any maintenance and produced with quality control assurance. SAT-507D is a basic model
satellite receiver. The technical information of the receiver will be explained in the
following pages.
2. POWER SUPPLY:
The TOPSWITCH concept is used in power supply. The switching and control circuit is
associated with IC03(TOP223). R251, C201 and D10 are protection circuit of IC03. The
5V regulation is provided by using IC06 (opto-coupler), secondary side components
(C135, D09, R221, R218, R220, IC08, C78, C274) which are coming to reference side of
transformer. IC02 (op-amp) and Q56 with external components generate the LNB voltage.
After the max LNB current or LNB short circuit controls are detected by Q07 and Q08,
the LNB power is cut-off by IC07. The 5V standby switching is made by (Q02). Q12
switches 13/18V. The 22kHz signal generated from IC01 (STV0042A) and it is switched
by Q10, Q11 and after amplified by IC02 than added to LNB voltage via Q56. In order to
reduce the power consumption in standby mode, Q03V switches off the 5V power supply.
When the double LNB inputs tuner is used, the switching of LNB powers is done by Q38,
Q40, Q35, Q39, Q34, Q29, Q25.
3. VIDEO CIRCUIT:
The composite video is first set to a standard level by means of a 64 step gain controlled
amplifier( Pin 17 of IC01 is base band video input ). In the case that the modulation is
negative, an inverter can be switched in. Then energy dispersal is removed by a sync tip
clamping circuit, which is used on all inputs to a video switching matrix, thus making sure
that no DC steps occur when switching video sources. The matrix can be used to feed
video to and from decoders, VCR’s and TV’s. Additionaly all the video outputs are
tristate type (high impedance mode is supported), allowing a simple parallel connections
to the scarts. After the video processing is finished, the external video enter to pin18 of
IC05. The sync of video is generated by R121, C45, R269 , C275, C46, R123, R227,
C177 and send to pin12 of IC07. According to decision of video, the selected video
(internal/external) is sent to the video outputs( scarts, modulator etc.) at pin16 of IC05.
4. SOUND CIRCUIT:
The two audio channels are totally independent except for the possibility given to output
on both channels only one of the selected input audio channels. To allow a very cost
effective application, each channel uses PLL demodulation. Neither external complex
filter nor ceramic filters are needed. The frequency of the demodulated subcarrier is
chosen by a frequency synthesizer which sets the frequency of the internal local oscillator
by comparing its phase with the internally generated reference. When the frequency is
reached, the microprocessor switches in the PLL and the demodulation starts. At any
moment the microprocessor can read from the device (watchdog registers) the actual
frequency to which the PLL is locked. It can also verify that a carrier is present at the
wanted frequency (by reading AMPLK status bit) thanks to a synchronous amplitude
detector, which is also used for the audio input AGC. In order to maintain constant
amplitude of the recovered audio regardless of variations between satellites or subcarriers,
the PLL loop gain may be programmed from 56 values. Any frequency deviation can be
accomodated (from ±30kHz till ±400kHz). In the typical application, the