LG 50' Plasma no picture

[cat22woman]

Hi, everyone. A guy from work gave me his TV because he thought it would cost as much to fix it as get a new one. It had a 3 or 4' black line at the top.

I used to be a computer/electronics tech in the navy, but I haven't really done any troubleshooting since I got out about 10 years ago. I figured what the heck, it may be an easy fix and I kind of miss troubleshooting, so I took it.

Did a little troubleshooting on symptoms (and Google is my friend!) and figured it was the top Y driver board. I replaced it and it worked beautifully for about a week. I was stoked as it was twice as big as my last tv and for less than $100!

Well, a week later the whole picture went out and I'm at a loss. I went and bought a multimeter and I've measure the Vs and Va voltage coming into the Ysus board, and it is good. From reading similar problems online it seems common to replace three boards, but I find that hard to take.

Please keep in mind I do not have an o-scope and so cannot measure waveforms, but would appreciate any guidance on what to do next. Thank you!

[cat22woman]

Re: LG 50' Plasma no picture

Sorry, forgot pictures.

[awyatt2]

Re: LG 50' Plasma no picture

look on the power supply, the voltages should be marked around the connectors. start by testing the power supply voltages. there are several different voltages feeding the other boards.

[cat22woman]

Re: LG 50' Plasma no picture

OK, I can try to take the measurements on that that I haven't already taken on other boards. I've been purposely avoiding the power supply because I have tremors and it's hard keeping the leads still. I figured with my luck I would end up touching something I wasn't supposed to. Plus, it didn't give any indication of a power supply fault according to the tech manual. But, if that's where you would start, it's easy enough. Thanks.

[awyatt2]

Re: LG 50' Plasma no picture

if you dont have startup voltage will it start? if you have no inverter voltage would it start? these are just examples to give an idea. one voltage low or missing is all it takes. i have fixed a large number of tvs because of a powerboard fault. fact is i am watching a 55 inch 1080p set right now i bought for 40.00 and it needed two diodes, guess where they were, power supply.you only have to be missing one for the tv not to start. good luck troubleshooting.

[retiredcaps]

Re: LG 50' Plasma no picture

I've been purposely avoiding the power supply because I have tremors and it's hard keeping the leads still.

You need something like this

http://www.pomonaelectronics.com/ind...=&parent=PATCH

[cat22woman]

Re: LG 50' Plasma no picture

if you dont have startup voltage will it start? if you have no inverter voltage would it start? these are just examples to give an idea. one voltage low or missing is all it takes. i have fixed a large number of tvs because of a powerboard fault. fact is i am watching a 55 inch 1080p set right now i bought for 40.00 and it needed two diodes, guess where they were, power supply.you only have to be missing one for the tv not to start. good luck troubleshooting.

Sorry, forgot to say there is sound, just no picture, so it is starting up.

Also, it doesn't really give a tolerance for the voltages. I assume .2 volts off is OK, is this not the case?

Thank you for your help.

[cat22woman]

Re: LG 50' Plasma no picture

You need something like this

http://www.pomonaelectronics.com/ind...=&parent=PATCH

I do need that! Now I'm remembering why I got out of electronics. Can't wait to see what happens with the soldering iron if I need to use it.

[awyatt2]

Re: LG 50' Plasma no picture

you may not be getting power to the backlights, usually 24 volts. you may need the soldering iron after all.

[cat22woman]

Re: LG 50' Plasma no picture

I read through some of the other threads on same TV, same problem. I realize I should have done that first, but I guess I searched for problem, when I should have been searching for model number. Which is LG 50pg20.

Anyway, towards the end of that, a poster had unplugged both y buffer boards and got same problem with one unplugged, and grey screen with the other. I unplugged the top Y buffer board (which is the one I replaced), and there is no change. When I unplug the bottom one, I get my grey screen and no input signal. I would assume that means bottom Y buffer is faulty, but one of the more experienced posters in that thread suggested it was the opposite for the other poster.

Do these boards freak out if you don't replace them at the same time? I did have a difficult time getting one without the other, and had to get it all the way from New Zealand!

[joshnz]

Re: LG 50' Plasma no picture

you may not be getting power to the backlights, usually 24 volts. you may need the soldering iron after all.

plasma tv's don't have back lights.

[awyatt2]

Re: LG 50' Plasma no picture

it is a possibility.unsure on that though, tom 66 would be the one to answer that question. i have only worked on one lg and it was a polaroid brand name, had cold solder joints on the connector.i have a samsung that has a bad top buffer and a bad ysus board but i plan on replacing upper and lower at the same time. try shop jimmy for the buffers and there is a plac inflorida sunshine circuit technoligys that has some boards reasonably priced.

[cat22woman]

Re: LG 50' Plasma no picture

Are you a nightowl too, awyatt2? I have been having a bunch of duh moments lately. I swapped the old, bad board on top to see if that was the issue. Same problem. So, I went ahead and ordered the bottom buffer from Shop Jimmy today cause I was feeling too lazy to take measurements before work.

My concern is that I find it strange that the bottom board went bad within a week of replacing the top one. I am quite rusty on my troubleshooting skills, as you can tell, but I hope there isn't something different or off in the newer boards causing the other to go bad. Otherwise, I may be playing a game that could get expensive! At least now I have two parts boards. I assume one of the four IC chips went bad on the top one.

[awyatt2]

Re: LG 50' Plasma no picture

some tv's will put the put the load on the weaker component and cause failure hence what you describe, no not a nightowl just work 2nd shift. i am into amateur radio and work on the tvs as a hobby. just something i enjoy doing. if a week was all you ran the top one and it was new you should be ok, maybe. i have a 50 hitachi that continues to run me up the wall. still working on it seems to be the xsus and am unsure on that cause i cannot find one failed component on the board.

[anrshelt]

Re: LG 50' Plasma no picture

I unplugged the top Y buffer board (which is the one I replaced), and there is no change. When I unplug the bottom one, I get my grey screen and no input signal. I would assume that means bottom Y buffer is faulty, but one of the more experienced posters in that thread suggested it was the opposite for the other poster.

Hmmm... By unplugging the top Y buffer, there is no change? Do you mean an ALL BLACK screen? Then, you unplug the bottom one, and get the grey screen? To me, it sounds just the opposite; if you're getting SOMETHING with the bottom one, isn't it the GOOD one, and the top the BAD one??

I'm reading through this because I have the EXACT same make/model I got for scrap (FREE) today.. I too, ran into other posts to where this seems to be where the TV is jacked up: THE TOP Y BUFFER.. BUT.. on this other thread, once they found that the LOWER Y Buffer was good, the 'PRO' told the 'USER' to press the menu button.. With the menu then NOT showing up on the Lower, Grey screen, he simply told him that he should purchase BOTH the Upper Y Buffer AND the Ysus boards (approx $150)..

So.. That's where I'm at with my problem.. UPPER Y Buffer is BAD, Therefore, the Lower Grey Screen.. Pressing Menu, I get nothing.. SO, I'm assuming I've cut the possible fix down to $150 thus far.. I'm going to look over the Ysus board tomorrow, and see if there isn't a simple fix (like replacing the glass fuse), try the 'menu' thing again.. BLAH!!

Finally.. You did say you replaced the TOP Y Buffer, and are getting the same results? or did it work for a bit and then take a dump on ya?? If you bought it, and just did the same as the old (replaced one), maybe this dang board (Top Y Buffer) is the main culprit of all of these LG 50PG20 SOUND, BUT NO VIDEO issuse; just a large manufacture of junk boards?? Would be nice for LG to hand out new boards to us, seeing it may be a problem in MOST/ALL of this model..??

~Drew. Portland, IN USA

[tom66]

Re: LG 50' Plasma no picture

You only need to replace the upper Y-buffer if the sustain doesn't damage the lower Y-buffer.