Lg 50pv450

[tom66]

Re: Lg 50pv450

OK, well both your Vsc (rated 150V) and -Vy (rated -190V) are high. For now, adjust Vsc so that when the set fires up, it reads around 150V (±3V.) Then tackle -Vy to ±3V. Adjustments are made by adjusting the "pots" (potentiometers), small little screw turns marked with the applicable voltage on the board.

[TennesseePaul]

Re: Lg 50pv450

Hi Tom
I tested the Vs and Va on the power supply. Each were a volt low. I adjusted each then tried the TV again. It had the same result. On for a moment then to black.
Tennessee Paul

[tom66]

Re: Lg 50pv450

Being a volt low on Vs and Va is not a problem.. for now, focus on the Vsc and -Vy.

[TennesseePaul]

Re: Lg 50pv450

Hi Tom,

Will do. Is it normal for these V's to drop off?

[TennesseePaul]

Re: Lg 50pv450

Hi Tom,

Do you know which direction goes up/down? The voltage doesn't ever hold making it difficult to tell if I'm changing any thing. I see 4 pots on the ysus. I believe I have the correct 2, they are the only two with these labels near them. But when I adjust them there isn't a noticeable change.

[tom66]

Re: Lg 50pv450

The direction usually isn't indicated, you need to just try and see.
As for which pot, can you take a picture of them? You might be adjusting Vsetup or Vsetdn.

[TennesseePaul]

Re: Lg 50pv450

Hi Tom,

Attached is the image.

Tennessee Paul

[TennesseePaul]

Re: Lg 50pv450

I'm able to measure the change in resistance on the pots. Turning counter clockwise reduces the resistance on the +VY pot.

[TennesseePaul]

Re: Lg 50pv450

Correction clockwise reduces resistance.

[tom66]

Re: Lg 50pv450

You should at least see some change in voltage, but try with both Y-buffers removed just in case.

[TennesseePaul]

Re: Lg 50pv450

Hi Tom,

I have attempted adjusting the volt. I believe I am close but it is difficult to tell as the voltage drops over time. Still no improvement in image.

Tennessee Paul

[tom66]

Re: Lg 50pv450

So you are able to get a reasonable voltage on -Vy and Vsc? If so, and the picture still looks poor, the Y-buffer must be at fault. Do you have the original buffers? Those look like replacements.

[TennesseePaul]

Re: Lg 50pv450

Hi Tom,
Unfortunately I do not. So you think both buffers need to be replaced? Could it be a bad panel?
Also, is it normal for the volts to drop as I am seeing?

Tennessee Paul

[tom66]

Re: Lg 50pv450

This is a newer LG panel which will detect a fault in the sustain/buffer boards and shut off if such a problem is detected.

I've not yet heard of LG panels going bad in a way that they kill the buffer boards.

[TennesseePaul]

Re: Lg 50pv450

Tom,

Well, that is nice to know. So, as far as we know, the panel is still good and there's a high probability of the Y-SUS being bad, correct?

Is there anything on the board, like an LED, which would denote a fault has occurred? I ask because, I haven't paid the logic board much attention, but I did notice when I had the lights out viewing the screen yesterday that there is an LED on the logic board which was blinking. It was the first I'd noticed it so I do not know if that is new or not.

Tennessee Paul

[tom66]

Re: Lg 50pv450

Usually the LED on the control board blinks once or twice a second if it's working. Don't know if these LG panels have a different code for failure mode.

The Y-sus is probably OK, actually, given the measurements.

[TennesseePaul]

Re: Lg 50pv450

Interesting. So if the board is OK, then it is normal to drop voltage over time for the two points?

[tom66]

Re: Lg 50pv450

No, that is due to the control board disabling the Y-sus. Brief output for several seconds is fine, indicating the Y-sus is working.

[TennesseePaul]

Re: Lg 50pv450

I disconnected the Ysus side connections from the two adjacent (left) boards, which I believe are the buffer boards, correct? I also disconnected the power from the Ysus to the Zsus board. I left all the ribbon connections intact.

I then powered up and attempted the measurements again. They did not drop off, but they also where much higher than I have previously read. They fluctuated still, bouncing between 500 and 400. I adjusted the pots with no real change in measurement. Now I am questioning my measurements. If I simply probed the board I read a very high voltage. Perhaps my voltmeter could be upgraded. Also I must double check, I am supposed to measure across the resisters with the Vsc and Vy labels, correct?

[TennesseePaul]

Re: Lg 50pv450

And, thank you for all your help with this. I really appreciate it.