LG 50PG20 Series, Training Manual

Page: 35 / 127

Plasma Spring 2009 50PG20
35
Power Supply Operation and Troubleshooting
Power Supply Basic Operation Power Supply Basic Operation
AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input Filter. Standby 5V
is developed from 330V source supply (which during standby measures 155V with relation to AC
Ground). This supply is also used to generate all other voltages on the SMPS.
The 5V (standby) voltage is routed to the Sub Micon (U701) on the SMPS and through P803 to the
Main PWB for Micon operation ( IC100).
AC detect Pin 18 of P803 is generated on the SMPS by monitoring the AC input and rectifying a
small sample voltage. This AC Detect Voltage is routed to the Sub Micon (U701) on the SMPS and
the Micon (IC100) located on the Main Board and is used as a basic “SMPS OK” signal. AC Det
actually releases “Reset” on the Main Board.
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 which enters the SMPS Board at Pin 19 of P803. The RL-ON
command is sensed by the Sub Micon (U701) circuit which causes the Relay Drive Circuit to close Relay
RL101 bringing the primary source voltage up to full power by increasing the 155V standby to 330V. At
this time the 16V and 12V source becomes active and sent to the Main Board via P803. The relay on
command on the main board turns on a 5 V general regulator that creates a 5V Det signal that is also set
to the Power Supply.
The next step is for the Micon (IC100) on the Main Board to output a high on M5V_ON Line to the SMPS
at P803 Pin 21 which is sensed by the Sub Micon IC (U701) on the SMPS turning on the M5V line which
is routed out P801 and P802 to the SUS boards. This same M5V kicks off the Control Board.
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 P803 on the SMPS Board which when sensed by
the Sub Micon IC (U701) turns on the VA and VS Supplies (VA is brought high before VS).