Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

[RoboDisko]

Hey. I'm fixing a PN51D530A3FXZA Samsung plasma TV Dated October 2011.

I figured out that there was a short on VS and traced it to the X-main board. I ordered a replacement board which came today. The replacement board is the same PCB and revision and model # etc, but has fewer components mounted on it. It has a total of 2 fewer MOSFETS, 2 fewer large capacitors, and several fewer small components. I didn't notice that it was different on the listing, but noticed fairly quickly when I had it in hand. I decided to install it anyways and see if it worked.

The TV seems to work fine with the board - for now. However, the VE voltage adjust is on the X-main, and on the replacement board with fewer components, I cannot get the voltage down to spec for the panel. VE spec is 80V, and with the pot all the way down (clockwise), the voltage only goes down to 82.1V. I'm guessing that VE is brought down from VS on the X-main, and the fewer component count makes it too weak to bring the voltage all the way down.

I ran the TV for a good half hour with the replacement board. Looking closely at the pixels revealed that there was more 'noise' than I think there should be. From a reasonable viewing distance the picture looked fine, but up close on darker images revealed that some random pixels flickered a little bit. I figure this mild irregularity is from VE being too high.

I'm also concerned that running the replacement X-main at max power may lead to an early failure, or running VE a little high might cause damage to the PDP.

OK so anyways, I've got 3 options:
1. Call the TV good and return it.
2. Use the good MOSFETS on the replacement board to fix the bad MOSFETS on the bad board. (assuming the MOSFETS are the problem, and I have the right MOSFETS to swap with on the replacement)
3. Buy another X-main with the right components. (the right one is now available on ebay for less than I payed for my current replacement. It's $19.50 FS)

What do you guys think I should do here?

[tom66]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

You've unfortunately got the 720p X-main, when your set is 1080p. There are quite a few differences between the boards which may cause picture diffusion issues. It might be possible to convert the 720p board to the 1080p version. The main problem is the 720p board is likely to fail pretty quick if you run it too long in a 1080p panel which draws more current.

The 1080p board is really hard to get hold of, lots of failures.

[ben7]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

You've unfortunately got the 720p X-main, when your set is 1080p. There are quite a few differences between the boards which may cause picture diffusion issues. It might be possible to convert the 720p board to the 1080p version. The main problem is the 720p board is likely to fail pretty quick if you run it too long in a 1080p panel which draws more current.

The 1080p board is really hard to get hold of, lots of failures.

Wouldn't it be possible to repair these boards though, since the transistors are discrete parts? (Not one of those pesky hybrid modules)

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

You've unfortunately got the 720p X-main, when your set is 1080p. There are quite a few differences between the boards which may cause picture diffusion issues. It might be possible to convert the 720p board to the 1080p version. The main problem is the 720p board is likely to fail pretty quick if you run it too long in a 1080p panel which draws more current.

The 1080p board is really hard to get hold of, lots of failures.

Would have been nice to know before I bought the replacement. Oh well.
They had a 1080p yesterday for 19.50 FS! Looks like its gone now though.

Wouldn't it be possible to repair these boards though, since the transistors are discrete parts? (Not one of those pesky hybrid modules)

That is kind of what I was thinking.

Any tips for identifying which of the 12 MOSFETS on it is bad? Is desoldering each of them individually my only option?

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

I checked the resistance on the base of the MOSFETS and found one that had the base shorted to the other leads. After removing Q4101, VS and ground were no longer shorted. I pulled the Q4101 from the replacement (720p) board, and I noticed that they were different models. Looking at the data sheets made it appear that they were similarly specced from different manufactures, so I went ahead and put the MOSFET on the original broken board. VS and ground remained not shorted, so figured everything was good. Powered it up and it did the same thing it had before, when VS and ground were shorted. The power supply attempts to raise the voltage for a few seconds, but it never gets higher than about 1.5v. Then it goes back into protect mode.

I doubled checked, and VS and ground are still not shorted. What could be causing the board to do the same thing as before, even though VS isn't shorted!?

[ben7]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

I checked the resistance on the base of the MOSFETS and found one that had the base shorted to the other leads. After removing Q4101, VS and ground were no longer shorted. I pulled the Q4101 from the replacement (720p) board, and I noticed that they were different models. Looking at the data sheets made it appear that they were similarly specced from different manufactures, so I went ahead and put the MOSFET on the original broken board. VS and ground remained not shorted, so figured everything was good. Powered it up and it did the same thing it had before, when VS and ground were shorted. The power supply attempts to raise the voltage for a few seconds, but it never gets higher than about 1.5v. Then it goes back into protect mode.

I doubled checked, and VS and ground are still not shorted. What could be causing the board to do the same thing as before, even though VS isn't shorted!?

When it shorted, it might have blown any chips that were controlling it, and/or it might have also blown a resistor and/or a diode or two.

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

When it shorted, it might have blown any chips that were controlling it, and/or it might have also blown a resistor and/or a diode or two.

I need to remember that I have a functional board to compare stuff to, to see if it is good.

I had already checked the resistance of whatever was connected to the base, and it is 10K on both boards, so I'm going under the assumption that whatever drives it is still good.

Looking a little bit further, I found 2 areas that I though were both VS and that is why they were shorted are actually not supposed to be shorted. Looks like another bad MOSFET. I'll be back when I've got it it replaced as well.

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

Ok I've ran into a question.
Original setup had 2 JRP30H1's in parallel. Collector and Emitter were both directly connected, and the bases both have a 15 ohm resistor to the same driving source, so 30 ohms base to base. One of the JRP30H1's has failed.

My replacement board has only 1 fgpf4536 in the same application. Would it cause issues to run the fgpf4536 with the RJP30H1 in parallel, instead of 2 matched IGBTs?

[tom66]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

Yes - you should only run them with matched IGBTs.
Mismatched IGBTs will turn on/off at different times - they have different switching characteristics. This may lead to one IGBT taking much more load than the other.

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

Ok.

I looked again and I found another one of the fgpf... ones. Swapped it in, turned it on, it turned on.

And moving along to my next problem...
After turning it on, it seemed to make more noise than I remember it having made with the 720p board. After about 30 seconds I could start to smell something, so it went back off. It seems that the IGBT I replaced first (Q4101) was putting out significantly more heat than it seems it should. After 30 seconds of being on, it's heatsink was too hot to keep your hand on, and quite a bit warmer than any other heatsinks.

I'm thinking 1 of 3 things is happening:
1. I'm being overly reactive, and its really fine (I doubt it, but maybe)
2. Whatever is driving the transistor is broken, and will break any transistor added until fixed.
3. The transistor was damaged during the transplant.
4. The different model IGBT from the 720p board isn't compatible with the 1080p board.

Any suggestions? Should I try running it for an hour to see if the transistor dies, or would I be better off replacing it?

[tom66]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

Well, the heatsinks do run hot.
I think the problem is you have put 2 x HD Board IGBTs in, when you really ideally need 2 x FHD Board IGBTs in.
Are the two inductors (coils in the rubber shields) identical to the 1080p board? Those might need to be swapped too.

[RoboDisko]

Re: Replacement X-main board with fewer components (Samsung Plasma PN51D530A3FXZA)

Well, the heatsinks do run hot.
I think the problem is you have put 2 x HD Board IGBTs in, when you really ideally need 2 x FHD Board IGBTs in.
Are the two inductors (coils in the rubber shields) identical to the 1080p board? Those might need to be swapped too.

Ok there are 2 different sets of IGBT's, and the one that is putting out the heat, and thus I expect is the problem, is the one that has the same model # IGBT's as it originally had.

FYI I'm doing component swaps on the original 1080p board, using the 720 for parts. So the coils are the 1080p coils. And a quick visual inspection, the coils appear the same. I didn't measure them or anything.