LG 50PQ30 Training Manual page 36

Power Supply Basic Operation
Power Supply Basic Operation
AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input assembly. Standby 5V is developed from
160V source supply (which during run measures 380V measured from the primary fuse F302).
This supply is also used to generate all other voltages on the SMPS.
The STBY5V (standby) is B+ for the Controller (IC701) on the SMPS and output at P813 pins 11 and 23 then sent to the
Main board for Microprocessor (IC1) operation. AC Detect is generated on the SMPS, by rectifying a small sample of the
A/C Line at D102 and associated circuitry and routed to the Controller (IC701) where it outputs at pin 15 and sent to P813
pin 18 to the Main Board where it is sensed and monitored by the Main Microprocessor (IC1). The AC Det in this set works
differently than most. If AC Det is missing the Microprocessor will turn off the television in about 10 seconds after turn on.
This will happen each time turn on is attempted.
A new feature included on the side keypad is called a Main Power Switch which opens a ground allowing the "Key On" line
of P813 Pin 24 to go high, turning off the 5V STB line defeating the Micro Processor (IC1) on the Main Board and Remote
Control Operation.
When the Microprocessor (IC1) on the Main Board receives an "ON" Command from either the Power button or the
Remote IR Signal, it outputs a high called RL ON at Pin 19 of P813. This command causes the RelaY-Drive Circuit to
close both Relays RL102 and RL103 bringing the PFC source up to full power by increasing the 160V standby to 380V
run which can be read measuring voltage at Fuse F302 and F801 from "Hot" Ground. At this time the run voltages 12V,
and +5V sources become active and are sent to the Main Board via P813 (12V at pins 5 and 6 and 5V at pins 9,10, and
12). The 5V detect line from the SMPS Board to the Main Board can be measured at pin 17 of P813. It is not used.
The next step is for the Microprocessor (IC1) on the Main Board to output a high on M5V ON Line to the SMPS at P813 Pin
21 which is sensed by the Controller (IC701) turning on the M5V line and output at P811 pins 9 and 10 to the
Y-SUS board P201 pins 9, 10. Then it is routed to the Control and Z-SUS boards.
Full Power occurs when the Microprocessor (IC1) on the Main Board brings the VS-ON line high at Pin 20 of P813 of the
SMPS Board. VS-ON is routed to the Controller (IC701) which turns on the 17V Audio, VA, and the VS supplies. VA and
VS output at P811 to the Y-SUS board. (VA pins 6 and 7 and VS pins 1 and 2). The 17V Audio supply outputs to the Main
board at P814 pins 1 and 2 and used for Audio processing and amplification.
AUTO GND Pin 22 of P813: This pin is grounded on the Main board. When it is grounded, the Controller IC701 works in
the normal mode, meaning it turns on the power supply via commands sent from the Main board. When this pin is floated
(opened), it pulls up and turns the Controller IC701 on in the Auto mode. In this state, the Controller turns on the power
supply in stages automatically. A load is necessary to perform a good test of the SMPS if the Main board is suspect.
36 November 2009 50PQ30 Plasma