LG 42LH90 Manual page 32

Power Supply (Main Power Switch Type 1) Location
Power Supply (Main Power Switch Type 1) Location
There are three types of Main Power switch used in LG televisions.
Type 1: Shuts off AC to the Power Supply.
Type 2: Opens ground to the front IR board. (Stand-By 5V Remains, the Main board stays alive).
This prevents any activity of the IR or the Key Board. When the Switch is opened, a line called Power Key pulls up high
when ground opens. When the switch is closed, this same line called Power Key feeds back to the Microprocessor and the
Micro. Turns on the Power.
Type 3: Opens ground to the front IR board. (Stand-By 5V turns off, the Main board is dead).
This prevents any activity of the IR or the Key Board. When the Switch is opened, a line called Power Key pulls up high
when ground opens. This line feeds back to the Main board and from there it routes to the Power Supply. The high tells the
Controller chip to turn off STBY-5V. When the switch is closed, this same line called Power Key now goes high and feeds
back to the Power Supply and tells the controller chip to turn STBY-5V on.
If the TV won't come on, be sure to check the Main
Power Switch before assuming a failure has occurred.
This switch breaks AC to the SMPS.
MAIN POWER SWITCH LOCATION
TYPE 1
(Bottom Left Side viewed from rear)
On Off
32 February 2010 LCD DV 42LH90