Circuit Description; Power Supply; Front Panel - Sharp DV-SV 80 H Service Manual

13. CIRCUIT DESCRIPTION

13.1. POWER SUPPLY

• Socket PL1 is the 220VAC input.
• 2.5A fuse F1 is used to protect the device against short circuit.
• Line filters and capacitors L1, C1, L5 and L6 are used to block the parasitic coming from the mains. They also prevent the
noise, produced in the circuit, from being injected to the line.
• Voltage is rectified by using diodes D1, D2, D3 and D4. Using capacitor C3 (470mf) a DC voltage is produced. (310- 320VDC).
• The current in the primary side of the transformer TR3 comes to the SMPS IC (IC3 TOP223Y). The SMPS IC has a three-pin
TO-220 case and a cooler is mounted on it. It has a built-in oscillator, overcurrent and overvoltage protection circuitry and runs
at 100kHz. It starts with the current from the primary side of the transformer and follows the current from the feedback winding.
• Voltages on the secondary side are as follows: -22V, -12V, 3.3V, 5V, 15V.
• D14 TL431 is a constant current regulator. TL431 watches the 5 volts and supplies the required current to IC2. There are a
LED and a photo transistor in IC2. The LED inside the IC2 transmits the value of the current from D14 to phototransistor.
Depending on the current gain of the phototransistor IC3 keeps the voltage on the 5-volt-winding constant.
• Adjustable voltage regulator IC5 (LM317) supplies 12 Volts.
• When the device enters stand-by mode, transistor Q2 starts to conduct and pulls the adjust pin of IC5 to ground, where this
cuts 12Volts off.
• –22 Volts is used to feed the VFD (Vacuum Fluorescent Display) driver IC on the front panel.
• Transistor Q4 and zener diode D14 are used to regulate +12 Volts. This voltage is used to feed op-amps on the back panel.

13.2. FRONT PANEL

• All the functions on the front panel are controlled by U7 (MT1379) on the mainboard.
• U7 sends the commands to IC2 uPD16311 via socket PL1 (pins 3,4 and 5).
• There are 16 keys scanning function, 2 LED outputs, 1 Stand-by output and VFD drivers on IC2.
• Pin 52 is the oscillator pin and is connected via R5 56K.
• LED D6 is red in stand-by mode and green when the device is on. When entering stand-by mode, pin 48 goes HIGH (+5V)
and controls the transistor Q2 on the power board.
• Vacuum fluorescent display MD2 is specially designed for DVD.
• The scanned keys are transmitted via IC2 pin 5 and 6 to U1 on the mainboard.
• IR remote control receiver module IC3 (TSOP1836) sends the commands from the remote control directly to U1.
• Socket PL2 carries the VFD filament voltage and –22 Volts.
13.3 BACK PANEL
• There are 1 SCART connector (PL4), 2 pieces RCA audio jacks, for audio output, 1 coaxial digital audio output JK3 and 1 laser
digital audio output PL5 on the back panel.
• TOTX176 is used for laser output.
• For coaxial audio output SPDIF is used.
• Q22 .. Q27 transistors are to mute the audio outputs while switching the state of the unit(power on/off)
• There are two op-amps in U14, U16 and U18. They are used for left,right,rear left and right, subwoofer center audio channels.
The feedback resistor is amplifying the gain.
• SCART pin 8 controls 16:9 and 4:3 mode using Q28,Q29 and Q30.
• When the pin8 output of the scart becomes 5 Volts, 4:3 mode is selected and 16:9 mode is selected when this output becomes
0. The circuit is adjusted to output 12 Volts for 4:3 mode and 6 Volts for 16:9 mode.
• Transistors Q28,Q29 and Q30 transmit these voltages when the device is turned on and cuts them off when it is turned off.
• FBL on pin 16 transmits 5 Volts via transistors Q12 and Q14 when the device is on.
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