Samsung PN50A450 - Flickering and Burn-In

[steveh_131]

Hey guys, here to ask you experts for a hand on a few tv issues. I've repaired them before with your help but they just won't keep working!

First one is this Samsung. I replaced the power board a few years back when it wouldn't power on and it's been a great tv, but now it's doing some strange things.

Here's a video: (Pardon the dryer sounds in the background!)

https://www.youtube.com/watch?v=BTjb7A_1GwE

I'm noticing the following symptoms:

• Burn-in from a round of castle-crashers a few days ago
• Flickering, which is more pronounced when there is more WHITE on the screen, invisible when the screen is mostly black
• Almost looks like snow on the screen, maybe a result of burn-in?

I thought this TV had burn-in protection so I'm not sure why it's showing remnants from past activities. But would that explain the flickering? Are the issues possibly unrelated? Thanks, guys! You've helped me rescue 3 tv's right now and I've had a great time doing it!

Steve

[Ltank]

Re: Samsung PN50A450 - Flickering and Burn-In

The video shows Mal Discharge. I highly suspect the Zsus board. It should be the right most board as viewed from the rear of the set.

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In

Ok, thank you.

Any ideas how I should test that? Or do I just replace it?

Also, does this explain the flickering alone or also the residual images?

Thanks again, you rock!

[Ltank]

Re: Samsung PN50A450 - Flickering and Burn-In

Usually I am limited to checking high speed switching diodes, transistors, mosfets etc. Check soldering joints on heat sinked
devices and recovery coils. I usually have not had capacitor problems on these boards. Rare but it does happen.

[Ltank]

Re: Samsung PN50A450 - Flickering and Burn-In

Not much you can do with burn it that I know of. Someone else might know. I rarely mess with the smd parts. Getting the oem
parts can be a pain

[tom66]

Re: Samsung PN50A450 - Flickering and Burn-In

Either Z-sus or Y-sus bad, leaning more to Z-sus myself, it can cause afterimages and apparent burn in (when there actually isn't any)

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In

Ok, it sounds like the Zsus is the consensus.

That seems to explain the snowy picture and the burn-in appearance, does it also explain the flickering on white images? The video shows it pretty well, any time the screen is mostly white there's a strong flicker.

Steve

[tom66]

Re: Samsung PN50A450 - Flickering and Burn-In

It's worth checking the various voltages on the boards: Vs, Va, Vsc, etc. Flicker on white could be Z-sus, Y-sus or Vs low from power board.

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In

Ok guys, I finally had a chance to pull the cover and do some investigation.

Here's what it looks like:



From what I can tell, there's a main board, logic board, x-main, y-sus, power board... no z-sus board.

The original symptoms persist, flickering on bright screen, remnants of past images. Now, though, I'm also noticing this pink haze on white areas of the picture.

I've read that this pink haze is called "banding" and that you need to adjust the Vs trimpot clockwise until it disappears.

Before I start tinkering, though, I'm curious if it helps point to a specific board causing the other issues (they're related, somehow) or this is just a coincidental problem.

I love this TV, I really hope I can fix it and I appreciate any help you guys can offer. You've all been a great help to me. Thanks!

Steve

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In

Ok, quick update, I now have learned that samsung's X-main is a zsus to he rest of the world. So that helps somewhat.

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In



The screenshot shows some of the haze and the artifacts.

[steveh_131]

Re: Samsung PN50A450 - Flickering and Burn-In

Ok, one more question for you guys.

My X-main (zsus) board is labeled
PCB NO: LJ41-05987A
PCA NO: LJ92-01515A/B/C/D

I've found a similar board here, except it's labeled A/B/C/D/E/F/G.

So, two questions:

What do the PCB and PCA models represent, exactly, and how close of a match do I need to find?

And is it worth spending $57 on a board that might not fix the issue, in your expert opinions?

Thanks, guys!

Steve