Samsung plasma TV PN51E550D1FX screen dims periodically

[Sryii]

I have a Samsung plasma TV PN51E550D1FX which has been flashing whole watching TV. But instead of getting brighter part of the image dims rapidly, from the top down. It seems to happen at random but also often if we change to a new source or if the screen changes suddenly.

I have the back opened up, I currently see no obviously bad capacitors but they're was one area on one board that was significantly dark. I've attached an image, it is at the end of the metal bar that says 51EF. They are two thermistors. Not sure if I can check them in circuit or if they have anything to do with the problems.

Any help or suggestions would be greatly appreciated, even though this is an older TV it is really great.

Link to YouTube video showing the flashing: https://youtu.be/g1GkY6uw7pQ

[tom66]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

The thermistors probably aren't causing your issue.

Interesting fault, though. Not seen this before. A first guess would be the Vs or Va voltage on the power supply board dropping out. Can you see if the issue occurs on bright scenes only? Or does it occur on darker scenes too?

If you have a multimeter, you can attempt to measure the Vs and Va voltages from the power board. But please be aware this involves powering the TV up with high voltage exposed on the power board. Avoid doing this without another person present - just in case. Vs is around 200 volts DC and Va is around 60 volts DC. The exact voltages are printed on the back of the plasma panel somewhere.

If my guess is right, you have a power board issue, and your Vs voltage may be sagging on high brightness scenes, because of a fault somewhere. But, I could be wrong.

If there's no variation in Vs/Va (or only a few volts - you'd need to see a lot of variation in the Vs/Va for this to cause the fault), we'd need to rule out the main board by operating the test pattern sequence.

[Sryii]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

It occasionally occurred on darker screens, such as the dark menu that my cable box has. I will measure those values and reply back later tonight.

Thank you for your help.

[Sryii]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

Vs and Va were exactly as listed on the back of the TV. I will try and run the test pattern sequence. I believe its the one where you have to jump to copper circles on the logic board right?

[Sryii]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

Okay, well I ran the logic board test panel and I don't see the flashing at all though I'm not sure if it is because it hasn't been on long enough. Time might not even be a factor for this issue.

What would be a good next step?

[tom66]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

I would leave the test patterns on for some time to see if the fault comes back. But if it does not, then the likely cause is the main board (the board with HDMI ports on it)

[Sryii]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

The test pattern only seems to stay on for ten minutes and then shuts the test pattern off. Oh well. I did try hiking everything back up and now its working fine. I'm not sure if this has to do with how long the TV has been on so I'm going to try running it for a few hours. I'll report back with any results. Thanks Tom for your help so far!

[ajshoe]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

Id check all the screws holding the axis boards and PSB. Or could be lose connection on connector. I'd check all connectors for tarnish or burnt areas

[budwich]

Re: Samsung plasma TV PN51E550D1FX screen dims periodically

what cell light setting do you have? Any other "auto" settings on (eg. dynamic contrast)? Not saying they are a problem but they might indicate what circuit may be in trouble... maybe?

You could try running some test patterns that exist on some dvd/bluray for tv setup or via computer file and see if you can determine anything from those.