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Standby Power
Overview
When this TV is plugged into AC, the standby power supply stage be-
comes active and outputs standby +12 volts and standby +5 volts. The
+12 volts are applied to the master power switch, which is routed to the
AC relay's coil when the switch is pressed (latched ON). The +5 volt
powers the Main Micro IC3251 and infrared receiver so they can detect a
power ON command.
Circuitry
There are several components that condition the AC input before reaching
the 60 Hz. standby transformer T5503:
AC Line Input Parts
Number
Purpose
Suppresses incom ing narrow voltage spikes by
VR5501
reducing resistance when a high voltage threshold is
reached.
T5501, T5502
Com m on m ode rejection transform ers to cancel out
of phase AC input or TV output noise.
R5518
Surge lim iting resistor
.
59
The standby transformer T5503 and bridge rectifier D5502 apply approxi-
mately +23 volts to +12 and +5 volt regulators. The standby +5Vdc goes
to the infrared remote control receiver and the Main Micro IC3521.
The standby +12 volts sent to the H1 board is applied to the Master Power
switch. As long as this power switch is latched ON, +12 volts is returned
to the high end of the AC relay coil RY5501.
The output of standby transformer T5503 is also applied to the full wave
rectifiers D5503 and D5504. The output is connected to the Main Micro
IC3521 to detect an AC loss. This provides enough time for the Main Micro
to save user settings into memory and cause audio and video muting just
before a complete power loss.
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