LG 50PJ350 plasma blowing Y-Sustain board

[chrismurphy]

Re: LG 50PJ350 plasma blowing Y-Sustain board

You probably dont want to hear this ,but its time to bin the TV
I have worked for years on plasma TV and when these boards go 50% of the time the repairs go the way you have seen.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

To answer Sam's question above, I definitely have respect for electricity and am fully aware of the damage and personal harm it can cause if something goes wrong. I'm not afraid of electricity and know how to take the proper precautions to not get injured besides the obvious not touching anything "live", I know what can hold a charge and safely discharge it before touching it.

My fear is actually just of anything that will pop or spark even though I know I'm not in any immediate danger from it. I'm generally very jumpy when it comes to any unexpected loud noise and I even jump when my phone rings quite often. I've never actually had anything harm me or even start on fire.
One of the worst scariest things I've had to do is back in the day when TV's used to be picture tubes instead of flat screens, and they had to be discharged to pull the chassis and unhook the anode lead. I used a 1 meg resistor in series with a couple alligator clip leads, one end going to ground and the other end clipped on a long thin screwdriver. Even with the 1 meg resistor, the big ones like 32-36" would let out a hell of a snap as I got close to the anode cap. I worked on my last one of those 14 years ago when I was only 40. I know I couldn't even do that now and the loud snap of the discharge would most likely give me a heart attack. It definitely seems to be getting worse as I get older. I'm hoping I can hang in there another 10-15 years til I can retire. Fortunately my regular job is mostly low voltage non-scary stuff.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Chris, I've had this thing since March and I'm definitely getting close to scrapping it. I happen to have 2 new spares of the transistor that popped and a few gate driver IC's. I plan to replace both and if it blows again, I'm done with that board. Then I'll try the substitute board that I've replaced all the shorted transistors on. And if that one blows, the TV is going to the recycling center. That 2nd board was given to me in need of repair by a friend who does all my LG TV main board work. He has the $10,000 machine to properly replace the main processor and I can't justify the expense for the few of those I do a year. A customer had sent him that board, but he doesn't fix that model cuz they're too much of a pain in the @$$ lol which should tell me something about how hard these are to work on because this guy is a master technician. The customer didn't want it back and wouldn't pay the return shipping so he sent it to me free along with an LG main board I had him fix. With 2 boards, I have a little better odds of getting at least one going. And his board wasn't blown out quite as bad as the original. And by comparing readings between the 2, I found the short on the gate driver IC.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Ok I tried the 2nd board the other night or I should say I had my friend try it when he stopped by my house to get something while I was at work cuz I'm still afraid of it. The 2nd board didn't spark, pop, or anything unusual, but it didn't light up the screen either. He reported that the power button on the remote would switch the red indicator light in the front of the tv off and on, but the screen stayed dark. But I wonder if it was off when he thought it was on and didn't leave it on long enough for the screen to light up. Does anyone happen to know on this model if the red light is a standby light (on when the tv is off) or if it's a power-on indicator? He turned it off and on a few times with no fireworks, so I may mess around with it myself this weekend now that I know it's relatively stable. I'm thinking of putting a meter on the VS voltage. Because this board came from a different set, it probably needs to be aligned. So I wonder if the panel voltage is just too low to make it light up? I really want to conquer this thing and get it running. I think I'm getting very close.

[Biruslapio]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Hi, I've repaired once the Y-SUS and Z-SUS for this 50PJ350 model, that was in 2017, I have no memory of the repair, only a file that I scribbled the details of what I replaced.
The components that failed in my board were 8 IGBTs(7 30F124 and 1 RJP63F3), one MOSFET(51N25) and one diode(RF2001).

This is what was on the 2017 file:

Y-SUS

Heatsink 1
RG2006 RPJ63F3(x) RPJ63F3 51N25(x) 51N25 K3667

Heatsink 2
K3667 RF2001(x) 30F124(x) RD2003 RD2003

Heatsink 3
RD2003 30F124(x) 30F124(x)

Z-SUS

RD2003 30F124(x) 30F124(x) 30F124(x) 30F124(x) RD2003

This was for my board, yours is probably the same layout and have the same compontents, check that please.
The components that have an (x) were shorted, replaced with original parts of same model, except for Y-SUS Heatsink 2 30F124, a 30F126 was put in place, no problems at all. Also probably some resistors were also open by the shorts, check your board for that, SMD gate resistors for the IGBTs(usually 15 OHMs or two 27 OHMs in parallel) and some 2R2 or 1.0 OHM through-hole resistors open when the board fails.

About the standby light, when the TV is off the red LED lights up, when it is on the LED shuts down.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I just wanted to give an update. I rebuilt that board that according to shopjimmy mentioned earlier in this thread is supposed to be a compatible replacement for my board. But with that one installed, the TV won't even power up, only clicks the relay when hitting the power button on the remote. But the good news is no fireworks and no FET's re-shorted so either it's not compatible or I missed something on that board.
So I replaced the 30F124's on the original board. (I had not replaced them after it blew the first time so I'm thinking the one that had a chunk blow out of it was probably weakened from the surge) After replacing it, the TV powers up, no sparks or explosions this time, but the picture is really fuzzy and grainy. So does the board need to be re-aligned after replacing all the blown parts (VS etc.) or is there still a problem with it? I hate to give up now because I finally got the screen to light up and it no longer blows anything on power up. I didn't let it run too long as I'm still a little afraid of it. But I'm still hoping to get it running just because I have about $100 invested in components so far.

[dick_barton]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I think that a lot of people probably suffer from the fear that after a repair, on powering up, it will go off with a loud bang.

I too have many years repairing equipment and must admit that I tend to step back prior to powering up and have even been known to put my fingers in my ears.

No, I don't think you are different to many people who repair equipment. After all who wants to see their work go up in smoke accompanied by a thunder clap.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Thanks @dick_barton, glad to know I'm not alone. Sometimes on the really scary stuff I've been known to run a 100' extension cord and power it up from the other side of the room lol. And because I don't like the spark you get when plugging stuff in, and sometimes it's even normal to get a little spark even if there's nothing wrong with the device being plugged in, I use a power strip with a switch so I can turn it on rather than experience the spark of plugging it in. Switching power supply circuits can be very volatile and can easily blow up if the slightest little bad component is missed. That's why I prefer the new LED LCD TV's over the plasma and old school CRT type. Definitely safer and much less potential for something to go out with a bang.

[Biruslapio]

Re: LG 50PJ350 plasma blowing Y-Sustain board

You may have replaced the 30F124s, but their SMD gate resistors and some 1.0 and 2.2OHMs resistors may be open in both Y and Z boards like i said in my previous post.

About fear of powering stuff on, if the components I replaced are multiple expensive IGBTs and they blow, I get mad actually, because it's money going down the drain.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

thanks for the reply. Funny you should mention the 2.2 ohm resistors, I missed that on your fist post. As luck would have it, I was probing around on the boards checking low value resistors and just discovered some open ones on both boards right before I got your message. I'm working on it as we speak. The board that lights up the screen weak and distorted has a 2.2 ohm for the VS section that's reading 5.1, over double it's rated resistance so I'm sure that's making a low/weak VS. And there's another pair of them in parallel completely open, R528 and R529
And the one that didn't power up at all had that same resistor (R503) completely wide open. I just happen to have a 20 pack of those in my spare parts so I'm replacing them now and I'll let you know how it goes. Hopefully good news and no more fire crackers.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Success! It powered up with no fireworks and I have a clear picture, well at least better than the first time. It's a little dim and the contrast isn't the best so I'm going to measure the VS voltage and see if it's within range. Or it could just be the brightness/contrast settings too? It's by a window that's letting in some bright sunlight even through the curtains and blinds.
One further question for anyone who knows anything about plasma's: I've heard lore that a plasma panel can hold a charge similar to a picture tube? Is that true, and how long does it take to discharge? The reason I ask is that I want to test my 2nd board and if it works put it up for sale on Ebay. I also have a 2nd set of buffer boards which are most likely good. I blamed them for the first explosion but the real problem was that shorted gate driver IC. 3 months, 3 blow outs, and having the board in and out about 1/2 dozen times, it finally works. Like they say, never give up! If you want something bad enough, stick with it. Thanks everyone for your input and help!

Edit 5 minutes later: Maybe I'm not out of the woods yet. 5 minutes after running it, I noticed the 30F124 heat sink is rather warm. Is it normal for those to run hot? I had it running for about 10 minutes prior to that. Also noticed an oops, I forgot to plug in the connector going to the Z sus board. That would explain the dim picture. But also if there's a problem on the Z board, it could still blow again. Well another minor setback but over all still going in the right direction.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Powered it up with the Z board plugged in and it let out a sizzle and pop, so time to junk it. Never working on another plasma, they're impossible to fix. This is #4 over the past 3 years and didn't have any luck with any of them.

[dick_barton]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I really like the picture quality of the plasma sets and the screens are not so easy to damage as so often is the case with the LED sets. You are correct that they are a sod to repair so I don't touch them.
Saying that my niece will be bringing her plasma set to me in a few days to look at and to be honest if it's not a power supply fault I doubt that I will venture any further on it other than possibly board changes.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Yeah that's what I thought this one was, "won't turn on" so I thought a simple power supply problem. Well 3 months later it's still junk. I hope you have better luck with yours. Some plasmas mostly Samsung's are known for power supply caps failing so hopefully you run into an easy fix. One last thing I tried last night is I unplugged the Z board because I had an ok picture the first time I forgot to plug it in. But now the video is pretty much unintelligible blobs and the 30F124 heat sink gets very warm in a short time. So I'm starting to wonder if I have an internal panel short? Or a problem on the Z board I missed. I found no opens or shorts giving it a once over. I'm considering giving it one last power up attempt with the spare Y sus board. It should work now that I replaced the open 2.2 ohm resistor. And if that one gets hot too then probably the panel. I hate to give up after getting so close but I can't see putting any more time or money into it.

[dick_barton]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I did thankfully. It looks like they forgot there was an on - off standby switch on the side of the set or I was verly lucky that something may have moved in it when it was being transported. Gave the circuit boards a good clean and made sure that all the securing screws were tightend up.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Would anyone happen to know if it's normal for the heat sink with the 30F124's on it, Q02 Q03, and D01 to get quite warm in a very short time? That was with the Z-Sus board disconnected. I had video but it was fuzzy blobs, nothing I could make out, and I didn't leave it run long. Just wondering if I should hook up the Z-Sus board and give it a go, or if these outputs getting hot so fast indicates a bad plasma panel drawing too much current?

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Ok I decided to try something. I have that 2nd Y-Sustain board I also made a repair attempt on. I swapped it in, and made sure the Z-Sus board and everything else were connected properly this time. After about 10 minutes running, that same heat sink I mentioned above is very warm, almost hot. That area is labeled "SUS_DN". I'm also getting bad ghosting from top to bottom. For example the channel I was watching had a test box in the upper left corner of the screen. And I could see a faint ghost image of it all the way down. Also a few spots of "blooming". So what I'm wondering is does the ghosting and that area of the board heating up indicate a shorting panel drawing too much current, or is the heating normal and I just need to align the board? The VS measured 207.3V and it's supposed to be 206 but I can't figure out what pot controls it. The VA is 60.2, supposed to be 60V so that one is almost right on. And for some reason in the menu, the color is set at 100%. I can adjust brightness and contrast but it skips right over the color and won't let me adjust it. Please let me know if it sounds like my plasma panel is bad. Then I'll junk it out and stop wasting my time. Thanks

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Here are a couple pictures of how the screen looks.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Here are a few more pictures that show the problem a little more clearly than my earlier post last night. The 1st one you can see a grayish shadow in the background of most of the picture, the 2nd one you can see the brighter spots on the blue bed blanket, and the last one the gold blotches on the guy's brown suit coat. Trying to figure out if I have a bad panel, bad board, or something mis-adjusted. I did check and adjust the VA, VS, VSC, and VY to the proper voltages indicated on the panel sticker. They weren't off by much more than 1 volt before I started. I also measured the Z bias on the Z sustain board and it's a perfect 95V just like it should be. The only adjustments I haven't verified yet are the Set-Up and Set-Down as they're very complicated and need to be done with a scope. I do have one but it went through a house fire in 06 and got damp from the water, and I haven't attempted to power it up since so I'm not sure if it even works anymore. Could those Set-Up and Set-Down adjustments being off very likely cause my display problem, or would it more likely be a bad board or bad plasma panel? The "Set-Down" heat sink is still running quite hot and I'm not sure if that's normal because I've never worked on this model before. I ran it around 10-15 minutes at a time and nothing has blown yet but I don't want to go to long until I know if that amount of heat is normal.

[Biruslapio]

Re: LG 50PJ350 plasma blowing Y-Sustain board

The Y-sustain is not working properly, does it make a bunch of noise on the Y inductors? If it does, that also happened to one LG TV of mine.

You can adjust Set UP/DN as much as you want, just remember their original positions or resistance, if the blacks start to get noisy and the white starts to show random pixels while TV is warmed, you need to adjust it.

I suspect some components are partially damaged, but not enough to make the whole board fail.