Panasonic TC-32LX70/70, Technical Manual

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37LZ85 Power Supply Description
37LZ85 Power Supply Description
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When AC is applied to the TV, the Standby circuit of the P board outputs STB5V to the A board. On the A
board The STB5V is converted to 3.3V to power the system control circuit (not shown in the diagram) for standby operation.
The STB3.3V is also applied to the Remote Control receiver and the power LED on the V board. The MCU (IC1100) of the A
board outputs the SUB_ON command to provide a ground connection to relay RL802 of the power supply board. On the A
board, the SUB_ON command is used to turn on a switch that provides STB5V to relay RL802 via pin 13 of connector
A04/P6. When the relay is closed, 370Vdc from the PFC (Power Factor Control) is supplied to the LCD panel for conversion
into 120AC. The 370Vdc of the PFC is also provided to the switch mode power supply for conversion into Sub+9V, BT+30V,
DTV+12V, SUB+5V.
If the power button (main unit or remote control) is not pressed within 15 seconds after applying AC to the unit,
the SUB_ON command goes low to disengage the power relay. As a result, only STB+5V is output to power the system
control circuit of the a board.
When the power button is pressed, the SUB_ON command goes high to repeat the same operation. The
voltages remain present until the unit is turned off. The MCU also provides the Panel_ON command to trigger the output of
PANEL+12V. This voltage is used to turn on the inverter PCBs for the production of 120VAC used to illuminate the backlights
of the LCD panel. The PANEL+12V is also used to operate the drive circuits of the LCD panel. The MCU also outputs the
Main_ON command to trigger the output of the SOUND+17V source.
When the power supply output is too high, an over-voltage detection circuit outputs a high to the A board to
trigger the shutdown of the unit. The power LED does not blink.
An over-current detection circuit on the power supply board monitors for short circuits. If a detection is made, a
high is output to IC1100 to shut down the unit and provide 3 blinks of the power LED.
Caution: The P board is to be exchanged only.