lg55ub850v

[newtothis]

lg55ub850v

Few posts on this one with no fix.

Usual symptoms of solid led on main with 5 blink led on psu.

Found bad mosfet for 12v tcon .. only .8v out

Replaced and have led for tcon on main and 12v hitting tcon.

Still no back-light.

So have both leds on main lit. All voltages present from PSU. Still getting 5 flashes on PSU and no power to drv_on.

[nomoresonys]

It's most likely the mainboard. probably same old bad bga solder connections.

[Diah]

So have both leds on main lit. All voltages present from PSU. Still getting 5 flashes on PSU and no power to drv_on.

it sound issue at LED BL

[newtothis]

BL are fine. Forced on by injecting 3.5 to pwron and drv. No flash from BL either... main never sends signal to drv.

No BGA issues... all packages removed and reballed.

Replaced ic100 and ic101 just in case.

No change

[nomoresonys]

Maybe trace drv on back through mainboard and see what it hits before the bga and check those components.

[nomoresonys]

Post a good focused picture of mainboard and one of the whole back.

[Diah]

BL are fine. Forced on by injecting 3.5 to pwron and drv. No flash from BL either... main never sends signal to drv.

No BGA issues... all packages removed and reballed.

Replaced ic100 and ic101 just in case.

No change

ohhh big work...
then what about if you simulate by slide out the wire of DRV_ON from PSU socket and jumper the pin as you did before to PWOR_ON... and turn on what will you have on the screen???