LG 50PJ350 plasma blowing Y-Sustain board

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I got the Set_Up and Set_Down adjustments made with the scope, but no improvement on the picture. In the white wash mode the picture has a red tint to it and doesn't look good at all. At this point, do you think it would still be worthwhile to swap that pair of IGBT's from the spare Z board, or just call it a bad panel and junk it?

[Biruslapio]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Yes, this is a problem with either the RJP63F3 or the 30F124 transistors, or whatever drives them, I suggest desoldering all the heatsinks and testing each transitor and diode one by one to ensure you won't have to mess with them again, if you have an original RJP63F3 compare it against the ones you bought, and the Z-SUS 30F124s with yours.

For last you can measure VSCAN and -VY with the oscilloscope to make sure they're flat lines and not noisy or oscillating.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Does anyone happen to have a parts list for the EBR63039801 and/or EBR63039802. The reason I ask is that I'm starting to 2nd guess myself on something. I replaced the gate driver IC for the 30F124's on both boards. I believe the location is U704, hard to see the last digit. It was definitely bad on my original board, Vcc to Ground dead short but it may have been ok on the spare board. But I changed it because I thought it looked discolored and may have taken a hit from those IGBT's shorting out. I no longer have the original IC's and didn't take a picture of them. Just wondering if I may have either mis-read a digit of the part number or got a different brand or something causing my problem? Also the EBR63039802 had been previously repaired and none of the IGBT's or Mosfets on the heat sink looked original. So I used the exact same ones that were in the EBR63039802. And someone had different value gate driver resistors on one pair of IGBT's so I changed them to match the original board. So if anyone has a parts list or happens to have one of these boards in their possession I'd like to see a picture of U704 or specs on a parts list so I can compare it to the ones I bought to make sure I got the right one. I got them on Amazon from a seller in China. Have there been any know issues of bad gate driver IC's or just the IGBT's?

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

@Biruslapio, good call, and many thanks! I was quite hesitant to do this at first because of the amount of work involved (18 screws just to hang the Y-Sustain board and they all have to be in, and 2 delicate ribbon cables that have been in and out way too many times already) and I honestly didn't believe I had bad IGBT's due to the 99.9% positive feedback rating of the sellers over thousands of transactions. But you obviously know a lot more about these things than I do and have a lot more experience. I was to the point of junking it so I thought what have I got to loose. What's one more evening compared to probably close to 100 hours I have into it.
To make things a little easier, I had already pulled all the 30F124's out of my original Z-Sustain board thinking the problem was in that board. Then I bought that spare one just for process of elimination and it didn't fix the problem so I just left it in. 1st I swapped a pair of those originals from the spare board into that spare Y-Sustain board my friend gave me. Installed it into the TV and the picture is absolutely beautiful. Rich colors, no ghosting or speckling, and in the white wash mode I actually get a clean all-white screen with no blotches.
But I wanted to make sure that it wasn't just a fluke, so I swapped another pair from the spare Z board into the original Y-Sustain board and the picture looks amazing with that one too. So I've proven with 2 different boards that the 30F124's I got from Ebay are bad or fake. Measuring Gate to Collector with the positive lead on the Gate, the Ebay ones measure 2.6-2.7 Meg Ohms, but the original LG ones from the spare Z board only measure 1.5 Meg Ohms. I've attached pictures of both for comparison if you want to see if they look fake. I noticed the originals have 2 indented dots, one on each end of the component body. But the Ebay ones only have a single one in the center. Lettering isn't quite as solid on the Ebay ones too.
And funny thing is now that center heatsink with them installed doesn't even get warm. However the outside black heat sink closest to the buffer boards with the other replaced IGBT's (RJP63F3's) now gets quite warm (on both boards) and it didn't before. Wondering if that's normal now that the set is working properly or if it's possible those could be bad/fake as well? And finally I want to replace the 30F124's on that spare Z board and possibly try another set of RJP63F3's on the Y-Sustain boards to see if they run cooler, can you recommend a reliable source or tell me how to find one that has good/genuine/working components?
Thanks again for all your help. 4 months and 4 pages of threat posts later, we finally got this one fixed!

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

It's actually the 51N25 MosFets that are getting hot on the top of the black heat sink, not the other IGBT's. Can those run hot for a long time without burning out? The heat sink was hot to the touch, not burning and I could keep a finger on it, but wouldn't want to keep touching it for more than a 30 seconds. I just want to make sure it's ok so I don't blow up my board again, especially now that I have a good picture.

[Biruslapio]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Glad to see that it worked, amazing, using the multimeter to measure Emitter to Collector resistance has saved me a lot with IGBTs.

Even 50ºC is enough to hurt a person after some seconds, so if it's not absurdly hot like 90ºC, it's fine, the RJP63F3 are the ones doing the most work, they are 630V high current IGBTs, so it's normal the heat up, don't know about the 51N25.

I always enable some level of power saving to dim the screen a bit, it lowers the heat considerably and increase the life span of the boards a lot, level 1 or 2 power saving is the best option, if the TV is being used in a dark environment, level 3 is good too.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

One final question: Is it normal to hear a very high frequency ringing/oscillation with the TV running? This is with the back still off and the open side of the back facing me, but it's pretty loud, similar to when my ears ring but not quite as high pitch. I just want to make sure it's not overdriving something. Been running it about 20 min so far an nothing has blown yet, but I'm still a little afraid of it.

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I'm also working on the same TV. Here are the symptoms https://photos.app.goo.gl/cgFEzQ5YE5vqzmdv9

I also happen to have two Y-SUS boards which I'm trying to repair
Both boards had Q22, Q24 and Q03 shorted. I now read through this thread and also discovered an open R503 on one of the boards.
Also, if I keep the TV on for more than a few seconds, it blows the FETs again.

Don't give up, I hope we can somehow work together through this and fix this plasma TV!

P.S. Here is the schematic of a very similar board if it may help (some Russian guy has drawn it)

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Mine is finally all fixed after 4 months and returned to its owner so yes persistence pays off. These very seldom have a panel go bad unless it's physically damaged. Mine had just about every MosFet and IGBT transistor on the heat sinks shorted. Q02, Q03 in Sus_DN section (middle heat sink, P/N 30F124 IGBT's) Q11 2SK3667 on inside silver colored heat sink, Q22 and Q24 RJP63F3A (IGBT's) Q26 and Q27 FDPF51N25 and Q29 2SK3667 (MosFets) on black heat sink closest to buffer boards. I had several open gate driver surface mount resistors open on the back side of the transistors. Most have 2X10 ohms in parallel for an equivalent resistance of 5 ohms. Some of mine only had one of the 2 open so I was reading 10 ohms instead of 5. Q26 and Q27 use 2X47 ohms in parallel. One of my 2 boards had both 2SK3667's shorted, the other only had one of the 2 bad. Also measure all the T0220 Diodes on the heat sinks. I didn't have any bad ones but I was told they've been known to short on occasion. They're easy to measure in circuit with the diode scale of your meter. And if any transistors around them are shorted, it will cause a short reading as well due to them being pretty much in parallel.
And one of my boards had a bad gate driver IC, Location IC 704 near the outside end of the small center heat sink. It was shorted VCC to Ground causing a lot of parts on my board to self-destruct almost immediately on power-up. It's an IRS21850 S21850 SOP-8 and I bought mine on Amazon.com. I bought the other parts on Ebay, and I did get some bad/fake IGBT's the first time around. It didn't cause it to self-destruct but they ran hot and my picture was not clear. They were the 30F124's. There have been quite a few bad/fake components recently so hopefully you got good ones. A bad one could definitely cause your problem. Another thing I would check is to make sure you don't have a shorted buffer board as that will overload the Y-Sustain board and can cause it to blow as well. It also wouldn't hurt to give the Z-Sustain board a once-over to make sure nothing is shorted. Or you can run the TV without it plugged into the Y-Sustain board. Picture will be dark and images will be ghost-like but you can eliminate it as a cause of the problem by disconnecting it. Also when you put the Y-Sustain board in, be sure to put ALL the screws back in. I know there are around 18 of them but they're all electrical points and grounds, and leaving any out can also destroy the board.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Also check the low value 1W through hole resistors, the 20 ohms and the 2.2 Ohms. They run in sets of 2 in parallel in most locations. Also forgot to mention that even though only one of the IC 704 gate driver IC's was shorted, I replaced that part on both boards because it looked a little discolored and they can easily take a hit when the IGBT shorts. So even if yours aren't shorted, it's possible they could be bad. Mine were replaced before powering up the 2nd board so I'll never know if that one was good. I bought a 10-pack on Amazon which I'll probably never use most of them anyway so I replaced the 2nd one as a precaution.

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Yes I will try to check all FETs and resistors
What resistance do you measure across big R437?
on one of my boards it's 150k both ways, and another board shows 150k one way and 200k if I swap the polarity...

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

On my board I'm getting 206K one direction and 180K the other, and the resistance slowly increases in the direction with the lower resistance, like it's charging a capacitor. In the diode scale it starts out at around 1.5V with the red lead towards the outside edge of the board and slowly increases and stops around 1.75V, and it reads open in the other direction. So the difference on yours could also be a diode junction just on the edge of being able to conduct with the voltage from your meter in the ohms mode so the difference between the 2 may or may not be relevant. Try in the diode scale and see if you get any conductivity. Do both boards blow after running a short time? I'd check for shorts on the bypass caps near that U704 I mentioned. That's how I stumbled upon the shorted IC by comparing readings between 2 boards and one had shorts across the capacitors by that IC. Pin 1 is VCC and Pin 4 is "Common"

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Yes I did check the IC 704 when you mentioned you replaced yours and mine reads good on both boards.
The original board had shorted Q22, Q24, Q03, I bought the replacement board and it died in a few seconds after I turned the TV on. I'm not sure if the replacement board was good though. But the Q22, Q24, Q02, Q03 fets were good, these were the only fets I checked on the replacement board before I plugged it in.
I also decided to use 30F125 instead of 30F124 on the original board just because I thought it's a better FET

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Did you fix both of your boards? Tested? so I assume asymmetric reading on R437 is expected and something is wrong on my other board where it reads 150k both ways

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Oh I didn't realize that your 2nd spare board was supposed to be a good one. The 2nd one I got was also blown out and I acquired it free. Good possibility something else on the TV is making it blow like the buffer boards and you mentioned already having a new set on the way. You can also measure your buffer boards for shorts by putting your meter in the continuity check mode so it beeps when you have a short. Put one lead on ground and carefully rake the other probe slowly across both sides of each ribbon cable connector where the ribbons from the panel connect. If you find a short, that's a bad buffer IC and could definitely explain your board blowing. Hopefully it's only that and not a bad/shorted panel.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

And to answer your 2nd question, Yes I did fix and test both boards. And I had the same bad image on both with the bad 30F124's and they both cleared up with the good 30F124's from the spare Z board installed. I'm not sure about the 150K each direction because I didn't have any problems in that area of mine. But there is an IC and some diodes near that resistor. The IC is most likely a gate driver. I guess it's possible something went bad in that area. But I'd probably concentrate on what's causing the boards to blow first then see if there's any noticeable difference in performance. Also where did you get the 2nd board from? Ebay? Was it advertised as good/working?

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Yes I bought it from eBay as "not tested" but it does not matter now as it's blown now.
I did check the buffer boards for continuity and it tested good, but as you can see the image on my tv is in the very bottom that makes me think it could be still something wrong with the lower buffer board. I had similar symptoms with another TV what had bad buffer IC.

Is there a way to check if the panel is bad?

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

I'm not seeing the image of your TV screen. The schematic is the only attachment I see. I don't know if there's a way to test the panel. It might be more a process of elimination thing. But if the bad spot is horizontal straight across a certain section then yes that's most likely a bad buffer.

[zape]

Re: LG 50PJ350 plasma blowing Y-Sustain board

here is a video https://photos.app.goo.gl/cgFEzQ5YE5vqzmdv9
If I keep it running longer Y-sus blows again.

[Keshenatech1]

Re: LG 50PJ350 plasma blowing Y-Sustain board

Not sure about that, I hope it isn't a bad panel. Perhaps another member with more plasma experience could chime in here? I'd guess a bad buffer would be more symmetrical, straighter lines and more defined.