LG 55LF 5800 no video,no sound or backlight

[waybel]

Picked up this 55 inch LG 55LF5800 . It has standby light but that's it .Blinks 3 times .No picture,no sound.Could hear rattling inside.Changed all led strips as half of the reflectors were broken.Put back together still no go .Checked output from power supply to LED connector .Only getting 89 volts on each .Suppose to be 215 V and 145 V . power board number is EAX65423801 .Yes i know screws are not on power board .I just put back on for pics.

[EazyBone]

3 red light means TV is turning on. Lgs do this, not an error code.

Do you see a picture with flashlight? Turn screen on and look for picture. May take a minute or so before you see the no signal or the smart bar. Also check 12v on each side of TCON fuse.

Sometimes the main board is bad and doesn't send signal to turn on BL so test that first. Also give voltage readout on the PSU for each pin going to main board.

[Storyteller12]

If I'm not mistaken these LG TVs “LF” series had problems with main boards. In particular the cpu overheats and goes bad. I don't recall anyone reflowing one to fix it either. Have to replace it unfortunately.

[waybel]

No picture with flashlight that i could see.12 volts on T-con fuse.All voltages are good going to main board

[waybel]

Saw someone mention possibly BLO202B led driver on power board .Hoping it's not main board.Probably worth more than tv

[lotas]

EAX65423801 schematic

[waybel]

Thanks to everyone and for the schematic .I am just learning and not great with schematics.I see the 89 volts i have going to both LED + .Obviously something is not turning them on to create the 215 and 145 volts needs to turn on the led strips.Any help appreciated on what to test/look for next

[lotas]

To start the backlight, the motherboard must supply these voltages to turn on the backlight driver, are they available?

[waybel]

no they are not.Top row are 3.5 12 24 volt

[waybel]

Has 3.5 12 and 24 volts but has no voltage on Pdim1, p-dim2 or drive on.

[lotas]

Well, here's the problem - motherboard, check the usb and hdmi ports for low or short resistance (signal lines), if they are ok, then heat the processor with a hairdryer (if possible, remove the radiator from it) and warm it up thoroughly without fanaticism for diagnostics.. .

[waybel]

Yes i crossed the standby 3.5 volts to drive on and power on and got the backlights working

[waybel]

I removed the heat sink .I have a hot air/soldering station .How long should i leave hot air on at 385 degrees on the processor?

[lotas]

Have you checked the usb and hdmi ports before heating the processor? If there is a short or low resistance on even one line, then the processor is no longer working properly. You can heat for 30-60 seconds.

[waybel]

Have you checked the usb and hdmi ports before heating the processor? If there is a short or low resistance on even one line, then the processor is no longer working properly. You can heat for 30-60 seconds.

I am not sure how or where to check the resistance

[lotas]

Then take a high-quality close-up photo of where these ports are located.

[waybel]

[lotas]

These are, from the processor side, relative to gnd.

[waybel]

the USB are all 1.8 the HDMI are 2.8

[lotas]

What are 1.8 and 2.8 Om, kOm, MOm?