LG 50PK750 screen won't come on

[tedj13]

I have an LG50PK750 that about 6 months ago started not turning on when I hit the power button. The red light on the front would turn blue and after a few seconds it would go out but the screen stayed blank. If I waited about 10 seconds and turned it off and then back on it would come on. Over the months it would take 3 or 4 tries before it came on. after a while I decided to just leave it on, and when I was done watching it, I would let the firestick plugged into it go to sleep. This worked fine until we had a power outage. Now the screen will not come on at all. I have done some troubleshooting, and thought maybe it was the voltage converter on the main board, so i replaced it but I still get the same thing. I have check all the resistors and they are OK. All the voltages coming off the main board are where they should be both when in standby and when turned on.
Any suggestions on what I should look at next? I know the TV is 10 years old, but I'd like to get it working so that I can put it in a bedroom. Thanks.

[tvtimmy]

Re: LG 50PK750 screen won't come on

Check these 3 resistors. They should all be right around 10 ohms. If one is not it is bad.

[tedj13]

Re: LG 50PK750 screen won't come on

Thanks, I checked them all and 2 are right at 10, and the third read 9.8.

[tvtimmy]

Re: LG 50PK750 screen won't come on

Check them again in continuity mode. I believe they are also fuseable?

[tvtimmy]

Re: LG 50PK750 screen won't come on

You can also try running the test patterns. There are many posts on how to do that.

[tedj13]

Re: LG 50PK750 screen won't come on

I'm a novice and I don't know what continuity mode means or how to do it. I have connected the 2 holes beside R51 and R52 on the control board, and I do not get anything on the screen.

[diif]

Re: LG 50PK750 screen won't come on

Did you also connect the cable between the mainboard and the control board ? (with the power disconnected).

[tedj13]

Re: LG 50PK750 screen won't come on

yes the lvds cable labeled p31 was disconnected, and when I turned it on I got the same response the light on the front turned blue for about 5 seconds, then turned red, and the screen stayed black.

[tvtimmy]

Re: LG 50PK750 screen won't come on

Continuity mode is when you touch both leads of your meter together and it makes a beep sound.

[tedj13]

Re: LG 50PK750 screen won't come on

Just to make sure I am running the test patter correctly, I have unplugged the TV, and after about 5 minutes I disconnect the LVDS cable P31. I then take a wire and insert the 2 ends in the holes labeled 51 and 52. I don't plug the LVDS cable back in. I then plug the TV back in and turn the TV on and should see something on the screen. When I do this the screen is blank. Does this mean the control board is bad?
Additionally I have found that when the TV is on I still get sound. I turned it up using the remote when the TV was on.

[nobbnobb1]

Re: LG 50PK750 screen won't come on

I fixed a 60PX950 recently which is similar to yours. If you tried to run the self test by disconnecting the ASIC board from the mainboard, then jumpering the two points on the ASIC board, there should be a pattern that shows up on the screen. It's very obvious and shows that the ASIC board + panel are good. If you tried to do this and didn't get a pattern then I would think you have a bad ASIC board.

I believe the chips on ASIC board are BGA soldered so as a last resort you could always try baking that board in the oven. Although most BGA related issues are on the main processing chip on the mainboard (under the heatsink).