Blinking Lights on LG 55LM8600 LCD Flatpanel after Lightning

[SurrealMustard]

I'm looking at this 55" LG LCD and it doesn't want to power up after a lightning storm. Pressing the power button makes the red light in the corner blink on and off and the LG emblem to fade on and off indefinitely until the power button is pressed again. siliconfish of the SiliconFish blog had a similar problem with a slightly older version of that set and found the issue to actually be the mainboard instead of the power supply. What would be the best way to confirm what the real culprit is?

[dick_barton]

Re: Blinking Lights on LG 55LM8600 LCD Flatpanel after Lightning

I think it would be best to take the voltage readings at the connector outputs and see what voltages you do/don't have.

[SurrealMustard]

measurements

With the back cover off, I can hear what sounds like a faint rapid-clicking or rattling sound from the mainboard. This is important because some of the voltages fluctuate in sync to this noise, which goes for 4-6 seconds and then pauses for 1-2 seconds before happening again. This'll go on for several tries until it gives up and goes back into standby mode. The measurements are as follows:

Connector P701
0v - "Reverse"
0v - "N. C"
.4-0v - "5CLK"
Ground - Ground
0v - "SIN"
.9-0v - "I2C_SCL"
.9-0v - "I2C_SCL"
0v - "VSYNC-IN"

Connector P201
24.7-0v - 24V
24.7-0v - 24V
Ground - Ground
Ground - Ground
3.5v - 3.5v
3.5v - 3.5v
Ground - Ground
0v - "VSYNC_IN"
0v - "DRV-ON"
0v - "N. C"
0-.4v - "P-DIM"
0v - "ERROR"

3.3-0v - "PWR-ON"
24.8-0v - 24v
Ground - Ground
Ground - Ground
3.5v - 3.5v
3.5v - 3.5v
Ground - Ground
Ground - Ground
12-0v - 12V
12-0v - 12V
12-0v - 12V
0-.4v - "P-DIM2"

[dick_barton]

Re: Blinking Lights on LG 55LM8600 LCD Flatpanel after Lightning

Can you run the power supply disconnected from the mainboard to see if it powers up the backlights and if the voltages come up and remain steady

If it doesn't power up can you, with the mainboard still disconnected, jump a 1K between PWR_On to the standby voltage 3.5V? and check the voltages are stable.

[SurrealMustard]

diagnosis error

Can you run the power supply disconnected from the mainboard to see if it powers up the backlights and if the voltages come up and remain steady

No dice, nothing with the mainboard disconnected.

If it doesn't power up can you, with the mainboard still disconnected, jump a 1K between PWR_On to the standby voltage 3.5V? and check the voltages are stable.

I would, but I haven't got a resistor handy. Can I improvise?

[dick_barton]

Re: Blinking Lights on LG 55LM8600 LCD Flatpanel after Lightning

Get one off a duff circuit board if you have any laying around.

[SurrealMustard]

Fixed!

Just to follow up, my troubleshooting eventually led to diagnosing a bad mainboard. Upon finding a replacement mainboard (very expensive in this model) and installing it, the set is working again (albeit without any of its previously-stored settings).

Another successful repair!

[dick_barton]

Re: Blinking Lights on LG 55LM8600 LCD Flatpanel after Lightning

Glad to hear it's up and running again.