LG 50PK950 Training Manual page 48

Power Supply Basic Operation
Power Supply Basic Operation
AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input assembly, routed to the two Bridge
Rectifiers D101 and D102 which then route the primary voltage to the PFC circuit (Power Factor Controller). Standby 5V is
developed from 158V source supply (which during run measures 390V 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 chip on the back of the board (IC701) on the SMPS and output at P813 pins
13 and 14 then sent to the Main board for Microprocessor (IC701) operation (STBY 3.49V RUN 5.15V).
When the Microprocessor (IC701) on the Main Board receives a "POWER ON" Command from either the Power button
or the Remote IR Signal, it outputs a high (3.26V) called RL_ON at Pin 15 of P813. This command causes the Relay Circuit
to close both Relays RL101 and RL103 bringing the PFC circuit up to full power by increasing the 170V standby to 390V run
which can be read measuring voltage at Fuse F302 and F801 (390V) from "Hot" Ground. AC Detection (AC Det) is
generated on the SMPS, by rectifying a small sample of the A/C Line and routed to the Controller (IC701) where it outputs
at P813 pin 16 (4.07V) and sent to P400 to the Main Board where it is sensed and monitored by the Main Microprocessor
(IC701). If AC Det is missing the set will not come on, the relays will click when RL_ON arrives, but then no other functions
from that point.
When RL_ON arrives, the run voltage +5V source becomes active and is sent to the Main Board via P813 (+5V at pin
5, 6 and 7). The (Error Det) from the SMPS Board to the Main Board can be measured at pin 8 of P813 (3.47V STBY and
4.11V RUN), but it is not used. The RL-ON command also turns on the 17V (Audio B+) which is also sent to the Main
Board. The 17V (16.9V) Audio supply outputs to the Main board at P813 pins 1 and 2 and used for Audio processing and
amplification as well as Tuner B+ once its stepped down to TU-5V.
The next step is for the Microprocessor IC701 on the Main Board to output a high (3.28V) on M_ON Line to the SMPS at
P813 Pin 17 which is sensed by the Controller IC701, turning on the M5V line and outputs at P812 pins 1 and 2 to the
Y-SUS board.
The Controller (IC701) also uses the M_ON line to turn on the VA and the VS supplies. (Note there is no VS On Command
in this set). VS is output at P811 to the Z-SUS board and VS and Va are output on P812 to the Y-SUS board P113.
(VA pins 4 and 5 and VS pins 9 and 10). Note: The Va is fused on the Y-SUS then routed out P114 to the X-Board Left.
AUTO GND Pin 18 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 AUTO GND is
floated (opened), it pulls up and places the Controller (IC701) into 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.
48 October 2010 50PK950 Plasma