LG 50PC1DRA - Screen slowy fills up

[grbgemen]

LG 50PC1DRA 50" Plasma

Was not powering on. Pulled power supply and found 12-15 caps that were bulged. Replaced all in question and now TV turns on. Problem is that something else is obviously wrong.

When I first power it on, only right side edge had a picture. Rest of the screen was black. Had no signal going to TV so it was just your standard fuzzy picture. I noticed right away that the picture was growing. The fuzzy static was spreading slowly, eventually filling up most of the screen.

While the screen was slowly filling up, I got the menu to pop up but it was hard to read. Almost as if the the colors were messed up.

I have attached a few pictures. I apologize in advance for the poor quality and viewing angles. I did not receive the TV with stand so it is kind of hard to take a picture while holding it. The pictures still show a black splotchy area that had not filled in. I shut it off before that area had filled in. I am not sure if the display will fill all the way up. Also note there is a dark square that can be seen.

Please note that I shut the tv on and off a few times and the screen seemed to stay lit where it had been. I have not turned it on for about an hour or so. Will go see if the screen has reverted back to mostly black. Will try and get some more pictures too.

Thoughts on the issue? I am not familiar with plasma tv's so dont quite understand how they work. Mostly dealt with LCDs and even at that, its been power supplies and inverters. Thanks!

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

This is in about 99% of cases the Z-sustain and the effect can range from blurry, dim picture to slow fill-in of the image with picture information visible. The Z-sustain is the righthand board mounted on the rear of the plasma panel, looking from the rear.

[grbgemen]

Re: LG 50PC1DRA - Screen slowy fills up

This is in about 99% of cases the Z-sustain and the effect can range from blurry, dim picture to slow fill-in of the image with picture information visible. The Z-sustain is the righthand board mounted on the rear of the plasma panel, looking from the rear.

Is this board fixable? If so, is it usually a cap situation or other failed components? Or is best to just replace it?

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

Check the fuse on it. If it's blown, replace it. If it blows when you power the TV up, or the TV won't power up any more, the IPM on the Z-sustain is shorted. The IPM(s) need to be replaced, which requires good soldering equipment.

Video from someone else doing a similar repair. He replaces all IPMs, but you only really need to replace the Z-sustain ones (likely only one is short; you can check it):
https://www.youtube.com/watch?v=Y8MNQYXw8E0

Replacement IPM:
http://www.ebay.co.uk/itm/4921QP1047...item416a84e5d1

Replacement Z-sustain:
http://www.ebay.co.uk/sch/i.html?_fr...kw=6870QZC004C

[grbgemen]

Re: LG 50PC1DRA - Screen slowy fills up

Thanks for the quick replies. I do not see any fuses on the Z sustain board. Perhaps it has surface mount fuses?

I am pretty handy with a soldering iron. Also have a good desoldering station too.

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

Is the board on eBay an exact match?

[Kingspin]

Re: LG 50PC1DRA - Screen slowy fills up

Could be a bad screen, i have seen similar that had a bad screen. The weak link is always the screen with flat panels. I would say 8 years is about the most use a flat panel screen will be good for , that includes both lcd and plasma.

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

I don't think it's a bad screen.

With plasmas when you get a bad screen, it's all or nothing. You either get a picture, or you don't. Or, you get vertical bands on the screen, due to driver failure. The plasma displays themselves can last a long time; the poor quality electronics are always the weakest link.

LCD screen failures are common too, but usually you can still see the picture. Only in rare cases does total screen failure occur.

[rayrod81]

Re: LG 50PC1DRA - Screen slowy fills up

While I agree that in most cases like this the culprit is usually the Z-sustain it is also possible that the Y-sustain contains the problem.

I have seen a few 42" LG 42V7 panels that had this exact problem and I could find absolutely nothing wrong on the Z-sustains. Finally, I pulled out the heat gun and cold spray and begun heating/freezing caps on the Z and Y-sustains. Use heat when the TV is cold and the picture is not filled in and the freeze spray when the picture fills in. If it is a cap the heat will speed up the process of the screen filling in and the freeze spray will cause the picture to revert back to when the TV was first turned on and the picture was not filled.

In my case, there was a single 10uF 450V cap on the Y-sustain that was not charging properly and was keeping the screen from lighting fully. In your case I would suspect the caps near the lower buffer connection (C143 i believe) and the cap near the stand up power board for the -Vy and Vsc (not sure of the board number). It is possible it could be one of these two and not the Z-sustain.

These caps will not be bulged in any way but will have "dried up" and not be able to charge the circuit properly. The usual culprits in this type of failure are caps with capacitance ratings less than 100uF and voltage ratings higher than 250V.

Once again, I am not saying this is definitely the fault but it is a possibility.

[grbgemen]

Re: LG 50PC1DRA - Screen slowy fills up

I went ahead and hit the Y-sustain board with a heat gun a bit ago and the picture did indeed feel the screen faster than it was before.

Here are a few pictures of what it looks like with a signal going to it. It has a very grainy picture. Not sure how to describe it. Fuzzy or static if you will. Is a faulty z-sus or y-sus causing this static or is this another issue on top of the slow screen fill?





To tom66, my z-sus board is 6870QZC004B while the one you listed is 6870QZC004C. Different revision? I did find the B version on ebay also. However will hold off on buying anything replacement parts till I can pin point the issue a little better.

Lastly, I appreciate all the help guys. Thanks!

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

If heating the Y-sustain worked, I'd suspect the ramp_up and ramp_dn voltages, as well as -Vy, and Vsc(w). The C should work for B, but it's probably a Y-sus issue. Also the predominant purple tint is due to poor discharge in the display -- high UV content (plasma displays work by converting emitted UV to visible light using phosphors.)

[grbgemen]

Re: LG 50PC1DRA - Screen slowy fills up

While I agree that in most cases like this the culprit is usually the Z-sustain it is also possible that the Y-sustain contains the problem.

I have seen a few 42" LG 42V7 panels that had this exact problem and I could find absolutely nothing wrong on the Z-sustains. Finally, I pulled out the heat gun and cold spray and begun heating/freezing caps on the Z and Y-sustains. Use heat when the TV is cold and the picture is not filled in and the freeze spray when the picture fills in. If it is a cap the heat will speed up the process of the screen filling in and the freeze spray will cause the picture to revert back to when the TV was first turned on and the picture was not filled.

In my case, there was a single 10uF 450V cap on the Y-sustain that was not charging properly and was keeping the screen from lighting fully. In your case I would suspect the caps near the lower buffer connection (C143 i believe) and the cap near the stand up power board for the -Vy and Vsc (not sure of the board number). It is possible it could be one of these two and not the Z-sustain.

These caps will not be bulged in any way but will have "dried up" and not be able to charge the circuit properly. The usual culprits in this type of failure are caps with capacitance ratings less than 100uF and voltage ratings higher than 250V.

Once again, I am not saying this is definitely the fault but it is a possibility.

See previous post about heat gun. I did pull the y-sus board out and looked it over. I did not have much time to mess today but did pull C143(47uF 160v) and it read 46uF. Cap near -Vy and Vsc was C50(33uF 350v) read 32uF.

If heating the Y-sustain worked, I'd suspect the ramp_up and ramp_dn voltages, as well as -Vy, and Vsc(w). The C should work for B, but it's probably a Y-sus issue. Also the predominant purple tint is due to poor discharge in the display -- high UV content (plasma displays work by converting emitted UV to visible light using phosphors.)

Can you explain what is involved in fixing the suspected areas(besides any caps) you listed? Also, I will try the heat gun again tomorrow to make sure that it indeed cause the screen to fill up faster.

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

Unfortunately, I've no experience with the older 50" LG plasmas, so can't offer much advice. ESR on caps can be high and cause problems too, capacitance can test fine or even higher than original.

[rayrod81]

Re: LG 50PC1DRA - Screen slowy fills up

Like Tom said, ESR is the important value when it comes to caps. I would definitely change those caps as they are both handling a lot of voltage and current and are probably part of the problem. The grainy picture is most likely caused by a bad wave form coming out of the Y-sus. You will need a 200MHz oscilloscope to properly read and adjust the waveform. Did you adjust any of the pots on the Y-sus or Z-sus?

[tom66]

Re: LG 50PC1DRA - Screen slowy fills up

Like Tom said, ESR is the important value when it comes to caps. I would definitely change those caps as they are both handling a lot of voltage and current and are probably part of the problem. The grainy picture is most likely caused by a bad wave form coming out of the Y-sus. You will need a 200MHz oscilloscope to properly read and adjust the waveform. Did you adjust any of the pots on the Y-sus or Z-sus?

Just as an aside, although the SM suggests 200 MHz, I have used a 20 MHz to see the waveform, and a 100 MHz DSO (Rigol DS1102E) to adjust it. But the Rigol is $400 and the 20 MHz one was about a tenth that.