Standby Operation
Standby Operation
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When the main power switch is activated, it is sensed on the A board by the MPU IC1100. The TV_SUB_ON
signal is subsequently issued in response on pin 8 of connector A4/AP4. It turns on the transistors Q7224 and Q7223 to
output the “Relay voltage on pin 15 of connector AP2/P2. The TV Sub_On signal is also provided to the relay via the
resistor R7208 and pin 17 of connector AP2/P2. This pulls the contacts of the AC relay on the P board. The AC input is
rectified and provided to the LCD panel for conversion into 24Vdc. The 24V is then provided to the inverter circuit of the
LCD panel to produce the 120Vac that powers the backlight CCFLTs. The same 24V passes through the P board and
enters the AP board for conversion into other voltages.
The over-voltage protection circuitry affiliated with each of the regulators located on the AP board monitors
for over-voltage conditions. It is designed to turn off the AC power by disabling the SUB_ON command that turns on the
AC relay.
When an over-voltage condition is detected on the AP board, the voltage at the base of transistor Q7207
goes “high” to turn on Q7207, Q7206, Q7205, and Q7204. The TV_SUB_ON voltage at pin 17 of connector A2/AP2 is now
grounded through Q7204 and the unit shuts down. To turn the unit back on, disconnect and reconnect the AC cord before
pressing the power button.
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