Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

[JonathanAnon]

Hi guys,

This TV is perfect when turned on, but after about 15-20 minutes of use, red dots appear on the screen and get progressively worse.. What I've tried.

- Replaced two main large filter caps (that were bulging) on the power board.
- Tweaked Vs, Va, Vscan etc to the values on the back of the panel
- Changed the pots on the Ysus board (I read through one of tom's threads with the instruction on how to do this).

I've noticed that when I use freeze spray/fans on the spot below the Ysus bank of caps, the problem disappears..

http://videobam.com/XlrmE

The hottest part seems to be the heatsink for the FETs on the IPM. But I cannot narrow it down further because the components are very close to each other. When I use the freeze spray in the white circle on the image below, the problem stops..



But the freeze spray has a wide enough dispersion area (even with the straw to direct it) so really any of the components in that area could be causing the fault. Oh, and I tried heatsinking that 16 pin chip, but to no avail.

The Ysus board is a Samsung LJ41-02088A Rev1.1 (other number on board LJ92-00981A) dated 08, so it seems that it may have been changed already given that the TV is from 05/06. I would just buy a new Ysus if I thought it would work with the other boards, but I know there are issues with matching the boards..

Any advice appreciated..

[tom66]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Try dropping Vscan by a bit; keep Vs and Va as-is.

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

- Tweaked Vs, Va, Vscan etc to the values on the back of the panel

that was the first thing I tried tom.. I focussed on Vscan (alone) having read a few different documents about similar issues with plasma screens and dots.... I turned the pot for Vscan counter clockwise, in stages, down to about 5-10 volts below the value on the back of the panel... But it didnt make any difference at all..

[tom66]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Did you try Yrr/Yfr?

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Yeah I found the thread you did which you advised on changing the pots on the y sus board.

http://unielectronica.com.co/imagenes/LJ41-02088A.jpg

You'll notice there are pots for Vsch, Yerr, Yfr, Yfrr, Yrr1, Yfrr1 ... I've tried toying with all of these, separately.. I started with the Yfr and Yrr, about a 90 degree turn of the screwdriver each time to the point where they would move no more.. Then I moved the pot back to it's original position and did the same with the other pots.. Nothing helped.

At this stage I was trying to focus on the fact that I can clear the dots by cooling the section that I pointed out in the other image.. But if you think it's worth having another shot at the Ysus pots, I'll certainly give it a shot..

[tom66]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

I would consider those two electrolytics next to the IC.

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

I would consider those two electrolytics next to the IC.

Yeah thats the next step I was gonna take with this y sus board.. they seemed okay with the ESR meter, but I didnt take them out of circuit.. I replace the three (two smd and one through hole) around that area just to rule them out..

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Just to confirm those SMD caps.. are 22uF 35V with tolerance of 5% (J).. right?

[tom66]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

More likely 20% tolerance.

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

okay I went down to my workshop, and took away the board with me.. Went through all my old boards but I dnot have a replacement for the two SMD caps.. So I'll have to order those in..

However, I've pulled out the through hole 20V 22uF electrolytic cap (to the right of the IC) from that section and it's measuring 0.5uF and 16ohm ESR... I went through all the caps the last time I had this board out, how the hell did I miss that..

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Just getting back to this now.. I changed that dodgy capacitor about two weeks ago, but didnt get a good chance to test it after... Have it on test with my PC, and it's about 90% sorted... There is still random speckles of green and red on a full white screen, but there is no full screen non discharge like in the video...

Trying to tweak it now to sort out the issue of the random red and green dots, so I have the back off it and am playing with the Vscan... They put the pot in THE most awkward spot, I have to turn off the TV to get at it safely..

[JonathanAnon]

Re: Neovia NEOPL-4950 Plasma.. the dreaded red dots :-(

Okay again after replacing that cap, the dots were down to about 10% of what they were.. Tinkered around with Yr, Yrr, Yerr, Yvsh on the Y Sus board but none mad any difference... Put them back to where they were and had a go at the Vsc pot on the PSU board... This did not affect things either.. Moved the Vs on the PSU and it's almost perfect now..