LG 42LK550 42" LCD powers on, no video, no backlight

[SurrealMustard]

This LG LCD acts like it powers up normally, but I'm getting nothing on the screen and no backlight (flashlight test reveals nothing on-screen). It can be turned off normally by way of the touch-sensitive power button.

Would this be a mainboard issue?

[ReeceyBurger123]

Re: LG 42LK550 42" LCD powers on, no video, no backlight

Stupid asking if its a main board issue, what about telling us what voltages you've tested ? Does Blon come up ? Does Pson come up ? Does the Pfc work ?

[SurrealMustard]

Measurements for "stupid" question

Stupid asking if its a main board issue, what about telling us what voltages you've tested ? Does Blon come up ? Does Pson come up ? Does the Pfc work ?

Well, the main power rails on the power supply (20volt, 12volt) are at or above their rated capacity. 3.5v is reading a little low at 3.3, but that should still be within the margin of error. Power-on is holding steady at 3.2, Error at 1.5, P-Dim at 2.8, A-Dim at 2.8, and inv on/off at zero.

[Andrew F. Ali]

Re: LG 42LK550 42" LCD powers on, no video, no backlight

Stupid asking if its a main board issue, what about telling us what voltages you've tested ? Does Blon come up ? Does Pson come up ? Does the Pfc work ?

...Well it would seem you do have a Main Bd problem as the Inv-ON is at 0. However, I had a Main Bd that tricked me and was sending the Inv-ON signal but the PSU Bd had a short to GND on the line and so I got no backlights. To really test it I had to cut the Inv-ON wire on the cable and realize there was Inv-ON from the Main Bd and the PSU Bd was the culprit after all.

[Sevenqi]

Re: LG 42LK550 42" LCD powers on, no video, no backlight

Try to reflow the main processor on the main board.