Power Supply; Microprocessor And Teletext; Video Processor/Comb Filter; Video Intermediate Frequency Section - Sanyo CE28FN1-E Service Manual

11. Power supply

First, let's define some TV states or working modes to clarify later explanations:
State Description
SMPS_B_LOW The power supply is in low consumption (low voltage). The deflection is stopped.
SMPS_B_HIGH The power supply works at nominal voltage. The deflection can be on or off.
STANDBY The micro stops "B_HIGH" port oscillation and the power supply is on "SMPS_B_LOW".
ON The power supply is on "SMPS_B_HIGH" and deflections are on.
ERROR_N Protect situation. The power supply is on SMPS_B_LOW and the micro shows the error by
the led indicator. The TV is not allowed to switch-on (except ERROR_5).
The power supply works in switched mode with "flyback" self oscillating topology and with control in current
mode. The outputs of the source are shown in the block diagram. Also there are:
• B8: feeds the power supply controller. The initial source in switch-on situation is extracted through
R803+R816.
• B9: feeds the optocoupler primary part.
The power supply sends two signals to the micro processor:
• -PD&FAIL: Switch-off immediately (mains off).
• 16/9&BSYNC: Mains pulses synchronism and 16/9 control. The micro analyses this line in order to switch
correctly from SMPS_B_LOW to SMPS_B_HIGH.
In STAND-BY mode all the voltage outputs are reduced except the microprocessor supply (it remains at 5
volts). The triac TR830 disconnects the PTC800 supply.

12. Microprocessor and Teletext

The microprocessor (IC100) main tasks are the following:
• video processor control
• audio processor control
• NVM access
• IR decoding
• Teletext processing and display
• OSD generation
• tuning and AFT
• failure checking
• ...

13. Video processor/Comb filter

The video processor (IC400) has the following functional blocks: video Intermediate frequency, mono sound
(not used), vertical and horizontal synchronism, geometry processor, video switching and filtering, colour
decoder and RGB processing. All the adjustments are performed by the microprocessor via the I2C bus.

13.1 Video Intermediate Frequency Section

• I.F Amplifier: The input signal comes from the tuner (TU250) through the S.A.W. filter SF200 (band pass
filter of the video information and the picture carrier.
• PLL Demodulator and VCO: The VCO does not need any adjust neither external coil. The frequency
adjustment is performed through the I2C bus. The components associated with the PLL are connected to
the pin 5 (PLLLF).
• Video buffer: The demodulated video signal is present at pin 6 (IFVO) with a typical level of 2Vpp.
• AGC: It controls the IF amplifier gain in order to maintain its amplitude constant. The capacitor connected to
the pin 53 (DECAGC) determines the AGC time constant.
• Tuner AGC: It reduces the gain when a high level aerial signal is received. The level at which this reduction
is performed is I2C bus adjusted (AGC in the service menu).
• AFC: The AFC information is accessible via I2C bus.
• Video identification: The video identification information is accessible via I2C bus.

13.2 Horizontal and vertical synchronisation

• Horizontal sync separator
• Horizontal oscillator: it is internal and only needs the crystal oscillator X400 as a reference frequency.
• PHI-1 detector: It is a PLL that synchronises the horizontal oscillator with the video signal. The components
associated with the PHI-1 are connected to the pin 43 (PH1LF). The PHI-1 time constant and the noise
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Service Manual MS CE25FN1-E