PL51D550C1G Plasma Samsung - No picture, but sound is ok

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Right now, it seems that -most- of the TV is working (voltages etc) but there is no picture. The crazy volts on X-main, in the very least, show that something is switching. And you might be able to hear a subtle buzzing from the electronics in the TV while it is operating.

I am assuming that when you tested the logic patterns, you jumpered pins 3 and 4 of the connector and unplugged the LVDS cable. This should result in a series of patterns on the display.

Check the plasma panel very carefully for cracks, including around the edge of the screen. A single crack will mean no picture at all. It is not like an LCD where a crack will cause part of the picture to go bad, it is very rare for plasma displays to have any image when damaged.

If there are no cracks I would try replacing the CONTROL (LOGIC MAIN) BOARD first. This is different from the MAIN BOARD, which is the board with the HDMI ports on it.

If you can borrow a scope, it would help confirm the fault. If not, it will have to be shot-gun diagnosis, replacing parts a bit at a time :/ sorry.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Right now, it seems that -most- of the TV is working (voltages etc) but there is no picture. The crazy volts on X-main, in the very least, show that something is switching. And you might be able to hear a subtle buzzing from the electronics in the TV while it is operating.

I am assuming that when you tested the logic patterns, you jumpered pins 3 and 4 of the connector and unplugged the LVDS cable. This should result in a series of patterns on the display.

Check the plasma panel very carefully for cracks, including around the edge of the screen. A single crack will mean no picture at all. It is not like an LCD where a crack will cause part of the picture to go bad, it is very rare for plasma displays to have any image when damaged.

If there are no cracks I would try replacing the CONTROL (LOGIC MAIN) BOARD first. This is different from the MAIN BOARD, which is the board with the HDMI ports on it.

If you can borrow a scope, it would help confirm the fault. If not, it will have to be shot-gun diagnosis, replacing parts a bit at a time :/ sorry.

Yes, I can hear a subtle buzzing from the eletronics and yes, I did this test that you mentioned on your post.
How do reach the plasma display, I have to disassembly everything, right?
Just one more question, even if the led on logic board is blinking indicating that everithing is fine, the problem could be the logic board?

Anyway, thanks a lot for helping.

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

If you want you can easily remove the front bezel, but even that is not really necessary. You just need to check the surface and edge of the glass.

I think the control board is working (blinking light) but not sending the right signal.

Could still be Y-main or Y-buffer fault but I'd be guessing at that point, hard to say.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

If you want you can easily remove the front bezel, but even that is not really necessary. You just need to check the surface and edge of the glass.

I think the control board is working (blinking light) but not sending the right signal.

Could still be Y-main or Y-buffer fault but I'd be guessing at that point, hard to say.

Looking from the front the panel is perfect. I'll try to disassembly and check. But what is strange is the fact that I heard a little "explosion" coming from tv but visually everything is perfect.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

I tried to turn on the TV removing the cables that connects logic board to Y-Main and X-Main (picture) to see if the led would still blinking indicating that everything is fine, and it did. It isn't supposed to blink indicating that something is wrong?
There is another way to test these capacitors with a multimeter (unsolder the capacitors from the board)?
What could be this "explosion" that I heard when the picture was gone?

Sorry about the questions. I'm trying everything before buying some board, because it's very expensive in Brazil, and buying from another country would take a lot of time to arrive here.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

If there isn't any light coming from the panel in a dark room, the problem could be the screen? There is no way to test to be sure if it is the plasma panel? I have to insist asking what could be that "explosion" that i heard before screen become black, because I think this could be the key to the problem.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Here are some pictures of my TV's screen. I didn't find anything wrong visually.

But what is driving me crazy is the fact that I heard a loud "explosion" coming from TV before picture disappeared (and I'm sure this is the reason of the problem), but I can't find any leads of what did "explode"

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Ve is ok, a slightly low voltage is acceptable if the image is not on.
On the X-main (http://i.imgur.com/9TSFJGL.jpg), there are three or four large red capacitors. Right next to each other, top left of board. Can you measure the voltage ACROSS these?

tom66, can I unsolder these capacitors and test one by one with my multimeter?

PS: my multimeter is like this one in the picture

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Maybe it's worth pulling the Y-main and X-main out and checking for shorted transistors and other devices.

That meter cannot test capacitors unfortunately.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Maybe it's worth pulling the Y-main and X-main out and checking for shorted transistors and other devices.

That meter cannot test capacitors unfortunately.

I think I can borrow a meter that can test capacitors, but I can't test using resistance test (like in picture below)?
tom66, just one more question, do you think the "explosion" that I heard is probably some capacitor that blew up (even that visually they are fine)?

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

If it was going to be anything, it would be a transistor failing.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

If it was going to be anything, it would be a transistor failing.

Hmm... As I didn't see any blown transistor or cap I will take my TV to a tech in my town. Anyway, thanks to everyone for helping

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Well, OK. But it's simple enough to use a meter to find shorted transistors. Components very rarely show signs of obvious damage.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Well, OK. But it's simple enough to use a meter to find shorted transistors. Components very rarely show signs of obvious damage.

How I can find shorted transistors? If you know some good video on internet i'll be grateful.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

After watch some videos on internet, I took off one transistor of X-Main board to test, and it is ok. But I think I won't test the others transistors because it was very difficult to me removing it. I almost melt the contact on the board, and now it is difficult to solder it again.

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

You don't need to remove the transistor. You can test across all three pin combinations (1-2, 2-3, 1-3) for shorts. That will tell you if it is shorted, which is how 99% of transistors, especially ones that go "pop", generally fail.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

You don't need to remove the transistor. You can test across all three pin combinations (1-2, 2-3, 1-3) for shorts. That will tell you if it is shorted, which is how 99% of transistors, especially ones that go "pop", generally fail.

I'm using diode mode on multimeter to test. It will work without removng it of circuit? I attach black probe to source, then quicly touch with red probe on left pin to actuvate the mosfet, them put the red probe on drain. This is how a guy do on a vídeo, don't know if it is the correct way to do this.

[tom66]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Whilst it's the proper way to check if a transistor is bad, it is extremely rare for a MOSFET / IGBT transistor to fail where it has not shorted. So you can just use diode mode to look for shorts.

If and only if there are no obvious shorts would I then try functionality testing.
The diode mode of the meter is usually not high enough voltage to turn on power MOSFET gate though, so I would use two 3V coincells in series.

That being said: 68 LCDs & 26 plasmas later... number of bad, but not shorted transistors = 1... and that one was leaky, in an array of transistors that had also shorted. So it was probably wounded by the other transistors failing.

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Update: I took my TV to a tech, he said the problem is on both X-main and Y-main and I should take my tv to Samsung assistance in order to change both boards, because he doesn't have it.
He didn't say how he have tested my TV and why he knows that the problem is both boards, he just said that is common when one boards fail, the other one fails too. I assumed as he said he doesn't have the boards to replace mine, he didn't test with good boards to be sure if picture works.
I'm not sure what i'm gonna do, because the led on logic board blinks indicating that everything is fine. But, because of the "explosion" I heard when my tv failed I'm think that the problem could really be X-main and Y-main (because both have big caps and transistors).
So... what board I should try to buy and replace first: logic board, or Y-main and X-main boards? Can I trust in shopjimmy? They ship to Brazil?

[rogerazambuja]

Re: PL51D550C1G Plasma Samsung - No picture, but sound is ok

Update 2: I had tested every transistors on X-Main and Y-Main boards using diode mode in my multimeter, and it seems there is no one shorted. Except one that I had tested every pins (1-2, 2-3, 1-3) and it showed "000" on multimeter LCD. It seems that it is shorted. Could it be the cause of the problem of my TV?
The transistor I'm talking about is SMK1360 on picture below: