VESTEL DVD7200, Руководство по обслуживанию

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0 to 0.4V: TV is driven by the composite video input signal (pin 19).
Left unconnected, it is pulled to 0V by its 75R termination.
1V to 3V: the TV is driven by the signals Red, Green, Blue and composite sync. The
latter is sent to the TV on pin 19. This signal is useful when using a TV to display the
RGB output of devices such as home computers with TV-compatible frame rates. Tying
the signal to 5V via 100R forms a potential divider with the 75R termination, holding the
signal at around 2V. Alternatively, if a TTL level (0 to 5V) negative sync pulse is
available, this will be high during the display periods, so this can drive the blanking signal
via a suitable resistor.
Control Voltage
0 to 2V = TV, Normal.
5 to 8V = TV wide screen
9.5 to 12V = AV mode
11.
CIRCUIT DESCRIPTION
11.1 POWER SUPPLY:
•
Socket PL2 is the 220VAC input.
•
2.5A fuse F1 is used to protect the device against short circuit.
•
Voltage is rectified by using diodes D1, D2, D3 and D4. Using capacitor C33
and C34 a DC voltage is produced. (310- 320VDC).
•
The current in the primary side of the transformer TR2 comes to the SMPS
IC .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, 12V.
•
D25 TL431 is a constant current regulator. TL431 watches the 5 volts and
3.3V 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 D25 to phototransistor. Depending on the current gain of the
phototransistor IC3 keeps the voltage on the 5-volt-winding constant.
•
When the device enters stand-by mode, transistor Q3 starts to conduct and
this cuts 12Volts off.
•
–22 Volts is used to feed the VFD (Vacuum Fluorescent Display) driver IC on
the front panel.
11.2 FRONT PANEL:
•
All the functions on the front panel are controlled by (MT1389 E ) on the
mainboard.
•
MT1389D sends the commands to PTC16311 via socket
•
There are 16 keys scanning function, 2 LED outputs, 1 Stand-by output and
VFD drivers on I.
•
Pin 52 is the oscillator pin and is connected via 56K.