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LG 47LW5600, No backlight, no sound, no picture but it turns on...

LG 47LW5600, No backlight, no sound, no picture but it turns on...

As the title says, this TV I am trying to fix for a friend of mine. The power on flashes twice red, then turns blue (on). However you get no picture and no sound.


"@kg1117 check the fuse on the T-con board and see if you have around ~12V on it. Double check the voltages on your LED connector again. 100V-300V is to much of a variation. Measure all the outputs on the power board to the main board and let us know what you find. Post some good pictures of your board with your question as well as the interconnect wiring. That way we can see what you see. Adding images to an existing question

This switch mode power supply develops Stand By 3.5V at all times when AC is applied. At power on, it develops 12V and 24V for the Main board.

It develops 50V for the LED Backlights.

The fuse F101 and F501 reads approximately 398V (from hot ground) during this time. The transformer T501 delivers an AC signal which is rectified and filtered by D201, D202, C201 and C202 which develops a Stand-By voltage of 3.55V which is used by the SMPS Controller circuit and is also sent to the Main Board It is output P201 pins 9~12 and sent to the P502 on the Main Board.

When the controller chip on the back side of the SMPS receives the PWR-ON command 3.41V via P201 Pin 1, it turns on the Relay RL101 which supplies AC to the bridge rectifier BD101. The primary section (Power Factor Controller circuit) increases its current supplying ability.

Both Primary fuses F101 and F501 now read a little more than 396V. D253 receiving switching pulses from L601 develops the 50V for the LED backlights. When the SMPS receives the DRV_ON command from the Main board via P201 Pin 18 (3.26V) it turns on the on-board Inverter to start driving the LED backlights. The backlight brightness is controlled by the Main board via PWM Pin 22 and Local Dimming signals via P832.

P201 Connector: (To Main Board)

3.5V_ST (3.55V) output P201 pins 9~12

12V (12V) output P201 pins 17, 19 and 21

24V (24V) output P201 pins 2, 3 and 4.

Turn on commands.

P203 Connector: (To Panel LEDs)

50V output P203 pins 1 and 13.

P832 Connector: (To the Main Board)

This connector receives the Local Dimming signals.

P202 Connector: (To Panel LEDs)

50V output P202 pins 1 and 12.

SMPS TEST 1: To Force Power Supply On.

Disconnect P502 on Main board.

(A) Jump pins 9, 10, 11 or 12 (3.5V) to pin 1. Test Voltage Outputs 12V, 24V to Main and 36V to the Inverter Section of the SMPS. Remove AC power. Leave the jumper in place. No Backlights at this time.


(B) Jump pins 9, 10, 11 or 12 (3.5V) to pin 18 (DRV-ON). Apply AC power, the Backlights should turn on. Note, the LED B+ will now jump to 65V then back down to 50V.

Note; If there is a problem with a load from the panel backlights, you can remove AC and Disconnect P202 or P203. When AC is reapplied, the Backlight LEDs should turn on for about 4 seconds and then shut off.

So, let us know what you find out"

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