LG 42LH90 _ LCD TV _ POWER SUPPLY BOARD CHECK

LOW VOLTAGE TEST - 1

AC Should not be applied at any time while adding resistors or while unplugging connectors as damage to the circuit Board may occur.

• When AC is applied ed, the SMPS “MUST” be producing STBY 5V on pins 7, 8, 9 or 10 of P201.
•  If 5V Standby is not being generated, the SMPS is defective and must be replaced.
•  There is no need to continue with the next test.
• But, make sure the Main Power  Switch is On.
•  Unplug P700 on the Main Board to make insertion of the Resistors much easier.

NO BACK LIGHTS DURING THIS TEST

• Add a 100Ω resistor between (5V STBY) pin 7, 8, 9 or 10 and Pin 2 (PWR).

• Apply AC. This will turn on the power supply.
•  Check that the 24V and 12V power supplies are turned on,

1.  P201 (24V pins 17 and 18)
2.  P201 (12V pins 13 and 14)
3.  P203 (24V pins 1 through 5) to the Inverter.

Remove AC power.

POWER SUPPLY BOARD BACKLIGHT TEST - 2

     P700 Connector disconnected from the Main Board. Apply AC after adding jumper.  Continue if the 1st test was OK. Leave original resistor in place.

• Add another 100Ω resistor between (5V) pin 7, 8, 9 or 10 and Pin 20 (INV On).
• Apply AC Power. Simulating a Power and Backlight On command.
• Backlights Normal:   If normal, the back- lights should turn on. SMPS OK, Inverter OK.

Backlights Abnormal:   Recheck all connections.   Confirm the INV On/Off line pulling up to at least 3V.

Remove AC power.

     Check the connections to the Inverter.  If the 24V was arriving at the Inverter in Test 1 (pins 1~ 5 of P203) and the Inverter On command (INVON pi n 12 of P203) is arriving, then see Inverter Section for further testing.