LG 50PQ20 Plasma no pic/no sound

[tw2005]

Re: LG 50PQ20 Plasma no pic/no sound

If nothing has been adjusted on the ysus board or psu you should not have worry about voltages but I'd check them once it's running.

But if it was me I'd go right over the ysus and check every FET,diode, resistor on the board and see if there's anything unusual like shorted FEts or burnt out resistors etc.

Maybe the training manual will help some although it's not the exact model the principles should be able to be applied.

Maybe check the voltage inputs to gnd at the connector and see if any short to gnd or low resistance? Likewise the Zsus feed at the Ysus?

That's all I can come up with for you I'm afraid.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

There's nothing visually wrong. How do you check mosfet or fets? I've just been checking the ohm and seeing if it matches similar ones, but I guess I should probably just enter the numbers in google huh? Does it matter what direction a metal oxide film resistor is soldered in? It doesn't seem like it should cause the ohm load is the same either way

[tw2005]

Re: LG 50PQ20 Plasma no pic/no sound

Oh, I see. resistors have no polarity, any direction.

I'd simply use diode mode and check there is no continuous beep to indicate short between any of the 3 pins. Or see if you can follow the training as the results shown are all in cct.

I youtubed to find out about testing FETs. there's some good videos arouund, Tom has some linked in a sticky very educational.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

So after some basic visual checks and the looking for shorts in mosfet/fet's I threw caution to the wind and hooked everything up. Still nothing, but a different nothing.
Now when I turn it on the front LED goes blue, flashes red and then it shuts off. I'm not smoking the resistors on the zsus (they're not even getting warm).
Now what?

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I disconnected just the Zsus and now I get sound, but I still don't have any picture.

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

That's quite unusual, it makes me suspect the Y-sustain or buffers are bad too

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

That's what I'm thinking too. Is there a way to check the ysus board & what part on it do you think likely failed?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

You need an oscilloscope unfortunately, especially with these new "combined ERC" plasmas.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

It's a 2009 so it's not that new. What's ERC stand for?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

Energy ReCovery, or, Energy Recovery Circuit.
New as in new technology. Only been around since 2008~2009.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I wish there was some way of making the screen at light up. It's basically doing the same thing it was doing before, except now that I replaced the faulty buffer board, it just shut off instead of frying the two zsus resistors.
What's a reasonable amount of money to invest in a set like this? If this was something one of you picked up, what would be your cutoff point? As it looks now, I'm probably going to need the stand or a bracket, zsus, ysus & likely the other buffer (though it looks fine to me). The boards aren't available on shopjimmy either so I'm stuck using ebay.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I have made a small bit of progress. Now everything (xsus, ysus & buffers) can be connected w/o anything smoking or getting hot, but there's still no picture. This may sound like a dumb question, but is there any sort of picture if there's no signal (eg static/white noise)?
I also rechecked the vs to the xsus and it's at 184.9 the +5 is at 5, which according to the sticker, is .1 under for each. Should that be adjusted?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

A slight glow on the screen accompanied by the input notification OSD.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

What about the vs & m5? Also if there's nothing being displayed (no glow or OSD) at this point, what's your guess as to what might be next: replace the other buffer board, ysus, or do you think the panel is bad?

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

Ever since I watched tom66's video on testing ysus buffers, I've been waiting for an opportunity to say "dodgy" and whenever time I find a problem on a board I say "oh that's not good, is it" in my best British accent.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I can't believe it! I removed the one buffer board that I didn't replace & I was finally able to get the screen to display something. Unfortunately it's only a bunch of pixels twinkling like stars & there's a 7.5 cm wide blank strip that runs vertically on side.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

If I have one buffer board connected I get a little bit of a pic, but mostly the pixels/stars, but if I have both connected, I get nothing. I'm confused tom66, help! Also I discovered that my main board had the s-video/rca input section just sitting there. I'm not sure what prompted the previous owner to remove it, but it's not necessary for it to be connected, is it?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

These sets chain buffer signals. With one buffer connected you will either get half a picture (could call it a "master" buffer) or nothing/noise (call it a "slave" buffer.)

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

Right but why am I getting a bit of a display when only one is connected (either one), nut if I connect both of them, I get nothing. And what about the rca input

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

So I tested the buffer boards and the one I did not replace is bad (I believe it's the first IC cause it's the contacts that go to FL 101, which I have no intentions of fixing). I was wondering, after reading the thread with jose6326, if the reason I began to get a bit of a picture is due to my adjusting the VS up a little? Sorry for asking so many question. I get obsessive about things once I start trying to fix them and have a hard time letting up until it's fixed (hence the hours I have spent reading every LG plasma thread remotely close to mine).