Samsung HP-T4254 got horizontal lines and 2-3" stripe

[Ijaz Ahmed]

Happy New Year to all...

I have got a HP-T4254 (NTSC model) Samsung plasma out of a junkyard. Upon inspection, it was found that the TV had missing main PSU board. I bought the PSU from China and the TV came to life. Let me admit that I had no idea that I need to adjust VS and Va (as the PSU had been changed)

I tested (for about half an hour) on composite Video In and VGA, it worked great. Then I took it home and connected cable to the TV and started auto program search (channel tune up) and during this process, the TV turned off with a small smoke and a strange blast type small sound.

Upon examination, the VIPer 22A in the standby power supply of the main PSU was found blown up. I changed it and TV came to life again but started showing horizontal lines and wide horizontal stripe on the lower side of the PDP. These lines are not pure black but the area glows somewhat (as can be seen in the picture)

Please see the attached picture and suggest me what else to check on the TV. What I guess is that it could be a bad chip in the Y-Buffer board. I have removed and reconnected all cables to the Y-Buffer but the problem remained there.

I have almost every tool and instrument in my lab, just need guideline from experts

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[tom66]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Could be bad plasma panel or bad buffer board/buffer IC. Pictures of the boards would help.

With a pitch black input video are the lines glowing with the rest of the panel or not?

[Ijaz Ahmed]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Hi tom66, thanks for a prompt reply. I will take apart the cover and take some pictures tomorrow.

At least in the wide stripe, I am sure it is not pitch black but there is glow with some reddish tone. You can also notice the two groups of white lines in the 2-3" wide horizontal black strip.

[Ijaz Ahmed]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

And regarding your doubt about the bad panel, I am just wondering if it is possible for a PDP to go bad when a standby power supply burns on a working TV. The only thing I can think of is that everything in the TV could have gone crazy as the power to the main AV board got interrupted while all other voltages were there.

[Ijaz Ahmed]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Changed the Y-Buffer, the problem remained as it is and at same locations.

Could it be control board ? I don't think about bad E, F or G boards because in that case, vertical lines should appear.

[tom66]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

I cannot see a control board fault causing this. It's possible if/when you moved the TV the panel got damaged/chipped on the edge? Also possible the ribbon cable is not fully seated.

The buffers are basically shift registers with data and clock - the control board cannot discriminate between individual lines.

[Ijaz Ahmed]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Quite a logical answer but why the black area/lines glow while the rest of the panel is displaying the picture ?

That is the only thing which is confusing me to think about electronic fault rather than a Y-electrode or panel damage.

Would a color pattern test help in finding something ?

[tom66]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Could the damage perhaps be on the Z-side of the panel? (X-main on Samsung panel.) You'd still get a glow, but it wouldn't discharge properly. Also, sometimes plasma cells can be affected by their neighbours, especially if the plasma panel is a little worn out.

[Alastair E]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

If the fault is unchanged with new buffers, the panel is no good.

The background glow in those dead areas will be leakage from the good areas adjacent to them.
Probably damage to the Kapton film tabs from the glass of the panel to the buffer-boards....
These cannot be replaced as are part of the panel itself.

[Ijaz Ahmed]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

I will examine the panel for any visible damage and do a color pattern test (don't know even there is some pattern test even available on this 2007 panel).

A local tech was telling me that if the +5V supply failed during the operation, it could have affected the AV board or the logic board. So I was thinking to do a color pattern test as well.

[Alastair E]

Re: Samsung HP-T4254 got horizontal lines and 2-3" stripe

Seriously doubt the AV board would cause that fault. Its just very slightly possible that the Control/Logic board could--but again Highly unlikely.

Check each Kapton film with magnifying-glass, you'll prob see a scratch or a small burn somewhere....