LG 42PG20 Training Manual page 22

CIRCUIT DeSCRIPTIONS
4
Board Voltage
VS
VA
Y-Sus
2
M5V VCC
16V
P
Main
5V
POWER SUPPlY OPERATION
G
Refer to the figures on page 25-27 . AC Voltage is supplied to the SMPS board at Connector
CN101 from the AC Input Filter. Standby 5V is developed from 340V source supply
(which during standby measures 159V hot ground). This supply is also used to generate
2
all other voltages on the SMPS.
The 5V (standby) voltage is routed to the Sub Micon circuit (IC701) on the SMPS and
0
through P813 to the Main board or Micon (IC100). LD703 will glow green to indicate
STBY 5V has arrived.
AC detect Pin 18 of P813 is generated on the SMPS by monitoring the AC input and
rectifying a small sample voltage. This AC Detect Voltage is routed to IC701 on the Sub
Micon on the SMPS and the Micon (IC100) located on the Main board. It is used as a
basic "SMPS OK" signal.
When the Micon (IC100) on the Main board receives an "ON" command from either the
keyboard or the Remote IR Signal, it outputs a high to RL-ON. This signal first turns on
a DC level shifter Q706 which creates 5V General. LD703 now glows amber indicating
5V General has been generated. This 5V General now provides the pull up voltages that
supply the output circuits to the SMPS. The RL-ON enters the SMPS board at Pin 19 of
P813. The RL-ON Voltage is sensed by the Sub Micon (IC701) circuit which causes the
Relay Drive Circuit to close Relay RL101. this brings the PFC source up to full power by
increasing the 159V standby to 340V. At this time the 16V source becomes active and
sent to the Main board via P813.
The next step is for the Micon (IC105) on the Main board to output a high on M5V_ON
Line to the SMPS at P813 Pin 21 which is sensed by the Sub Micon IC (IC701) on the
SMPS turning on the 5V VCC line. The last step to bring the supply to "Full Power" occurs
when the Micon (IC100) on the Main board brings the VS-ON line high at Pin 20 of
P813 on the SMPS board which when sensed by the Sub Micon IC (IC701) turns on the
VA and VS Supplies (VA is brought high before VS).
Note: If a voltage is missing, check for proper resistance before proceeding.
22
PDP Training - Fall 2008
SMPS Outputs
Description
Drives the display panel Horizontal Grid
Responsible for display panel Vertical Grid
Used to develop Bias Voltages on the Y-Sus,
X-Drive, and Control boards
Audio B+ Supply
Control Circuits
Adjustments
Voltage Location
VA RV901
VS RV951
M5V VCC Fixed