Samsung 50" plasma blank screen

[netdent]

Re: Samsung 50" plasma blank screen

I think I scrapped one of these sets that had a bad panel, not damaged just had a black line otherwise it worked well, just in case you get stuck for a board

thanks Ronnie

[rmoody]

Re: Samsung 50" plasma blank screen

Here's a good service manual that might help if you haven't read it yet. Kind of hard to see but you can upload another document and download a pdf of it for free.
http://www.scribd.com/doc/34870662/S...sma-Pn42a450p1

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks. Ronnie
There are quite a few boards on ebay - if I decide to go that route.
I'm grasping at straws right now.
I don't know if this pertinent, but one of the buffer boards is quite warped - see the attached pics and the components are touching the aluminum shield or heat sink.
I noticed it when I removed the bracket that secures the stand.
Peter
Pictures wouldn't upload

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks for the link - I'll check it out.
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks for the link - I'll check it out.
Peter

[netdent]

Re: Samsung 50" plasma blank screen

Thanks. Ronnie
There are quite a few boards on ebay - if I decide to go that route.
I'm grasping at straws right now.
I don't know if this pertinent, but one of the buffer boards is quite warped - see the attached pics and the components are touching the aluminum shield or heat sink.
I noticed it when I removed the bracket that secures the stand.
Peter
Pictures wouldn't upload

Hmm! if one of those is stuffed it's curtains, if I remember right the ribbons are permanantly attached to the plasma screen

[tom66]

Re: Samsung 50" plasma blank screen

On most Samsungs, a failed X board means the panel is useless. It MAY be possible to repair it, more than likely you've just got a cold joint - but if some traces are broken internally, then it's pretty much impossible...

[Tweek4]

Re: Samsung 50" plasma blank screen

What are the symptoms of a failed buffer board- before I attempt to remove it?

Peter

[tom66]

Re: Samsung 50" plasma blank screen

What are the symptoms of a failed buffer board- before I attempt to remove it?

Peter

An X buffer failure often leads to a loss of picture in certain columns or across the whole screen. Your symptoms do match a failed X buffer and finding a bent board seems to suggest this is a probable cause.

However - the X buffers are most likely soldered to the panel ribbons. They are not removable because of this. Any repair you do can only really consist of touching up joints on these boards or replacing failed components, as they are not replaceable.

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks for the help.
I read the manual linked in post#42 and started the checks for no picture, and after the first Vs and Va check, the result indicated to replace the power supply board, then the troubleshooting sequence continues(if not fixed by the new board) to check and replace (possibly) x, y, logic boards. Since I don't have the boards readily available, it could be very drawn out and expensive.
The manual did indicate that the buffer boards E and F (the warped board) are removable, so I may remove them and do a component and solder joint check.
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

To elaborate on my previous post, the first step in the manual for troubleshooting no video with audio is to disconnect the cables going between the power supply board(smps)
and y, x and main boards and check if Vs and Va are normal.
First, I disconnected all three boards and Vs and Va measured zero.
Then I reconnected the main board only and Vs and Va measured normal(207v and 56v).
According to the manual the smps board needs to be changed.
Does this sound reasonable

[tom66]

Re: Samsung 50" plasma blank screen

To elaborate on my previous post, the first step in the manual for troubleshooting no video with audio is to disconnect the cables going between the power supply board(smps)
and y, x and main boards and check if Vs and Va are normal.
First, I disconnected all three boards and Vs and Va measured zero.
Then I reconnected the main board only and Vs and Va measured normal(207v and 56v).
According to the manual the smps board needs to be changed.
Does this sound reasonable

No... The voltages are only present when the main board tells the power supply to switch on. As Vs/Va are present, SMPS is most likely okay.

[Tweek4]

Re: Samsung 50" plasma blank screen

I had similar thoughts. However the manual is a little confusing, as follows:
The diagram in the manual(photo,actually), shows the cable from the smps board to the main board to be disconnected quite clearly, but the socket number given is the adjacent connection which goes to the logic-main board. I disconnected that one after reconnecting the main board and I read zero volts. So.......???
Peter

[tom66]

Re: Samsung 50" plasma blank screen

I had similar thoughts. However the manual is a little confusing, as follows:
The diagram in the manual(photo,actually), shows the cable from the smps board to the main board to be disconnected quite clearly, but the socket number given is the adjacent connection which goes to the logic-main board. I disconnected that one after reconnecting the main board and I read zero volts. So.......???
Peter

I'm not sure. But the fact that you have some kind of display (even if just dimly lit) probably means that the power supply is okay. I have no idea if the manual is correct but it doesn't seem right.

[Tweek4]

Re: Samsung 50" plasma blank screen

Well, you are correct, the E and F buffers are permanently attached. I removed the aluminum shield to have a close look but I couldn't see any evidence of failure.
One think you may help with - I have been unable to find the test point for the Vsc voltage (-190v). I did find the pot that adjusts the voltage but no pin or solder pad.
There is a resistor adjacent mounted vertically on the Y board that has "vscan" silkscreened next to it.
Peter

[tom66]

Re: Samsung 50" plasma blank screen

Well, you are correct, the E and F buffers are permanently attached. I removed the aluminum shield to have a close look but I couldn't see any evidence of failure.
One think you may help with - I have been unable to find the test point for the Vsc voltage (-190v). I did find the pot that adjusts the voltage but no pin or solder pad.
There is a resistor adjacent mounted vertically on the Y board that has "vscan" silkscreened next to it.
Peter

You need to measure Vscan across both ends of the resistor.

Show a picture of the damage it MAY be repairable.

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks, Tom66...
There is no damage evident. Just the warped board picture attached to my post # 43.
Since it is the component side that is touching the aluminum shield, I am not sure that is even a problem. I have placed some plasticine type putty ( that yellow semi-sticky stuff) between the board and the shield to separate them. I'll check the Vsc voltage shortly.
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

Here is a picture of the suspect area of the F buffer, with the aluminum shield removed.
No apparent damage-arcing etc.
Vsc measured -190vdc, normal.
So- I may resolve to remove all the boards in sequence and look for a dry joint.
If this were a hifi project I would be tracing the signal circuits rather than power circuits.
Is it worth checking all the video signal ribbons for continuity?
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

F buffer

[tom66]

Re: Samsung 50" plasma blank screen

Here is a picture of the suspect area of the F buffer, with the aluminum shield removed.
No apparent damage-arcing etc.
Vsc measured -190vdc, normal.
So- I may resolve to remove all the boards in sequence and look for a dry joint.
If this were a hifi project I would be tracing the signal circuits rather than power circuits.
Is it worth checking all the video signal ribbons for continuity?
Peter

Checking for continuity could be useful. If you do hifi do you have a scope? Even a basic 20 MHz one can "see" if the waveforms are there or not.