Samsung PS50Q91HD sound but no picture.

[rowage]

Hi everyone,

Have this TV and recently encountered this problem. Can change channels, etc (I know this from the change in sound) but no picture - no light coming from screen at all.

So I grabbed out my DMM and tested:

Voltages from PSU:

Vs according to sticker is supposed to be 207v
Va is supposed to be 63v
Tested Vs to X and Y mains - all 208.5v
Tested Va - 63.5v

Then I isolated each Y buffer individually - no change.
Isolated Y-main - no change.
Isolated X-main - no change.

No idea what else to do. Please let me know if you can help!

Thanks!

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

Is there an indicator lit up on the Y-main board?

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Yes, a continuous light. Green from recollection but might possibly have been red.

Thanks Tom.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Sorry, I lied. The light was on the Input board, not the Y-main. There are no lights on the Y-main.

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

OK, in a dark room, can you see a faint glow from the screen being emitted? The green light on the Y-main would light up if the Y-main has a fault.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Hi again Tom, I found this quote from you regarding the same TV model, so I thought I'd reproduce it here and answer the questions you asked on that post as you must suffer from a lot of repetition and I would like to avoid it for you if I can :-)

- Turn out all the lights in the room and make it very dark. Does the screen appear to glow very faintly? There might be an image or it might just be a dark level glow. If it does glow, it is likely the Z-sustain/X-main that is at fault. If it doesn't, it's a Y-sustain/Y-main, buffer or panel fault.

* No glow that I could detect at all *

- Do you hear an audible buzzing sound from the X-main and Y-main?

* Faint buzzing from Y *

- Are there any fuses on the X-main and Y-main boards? If so, check these.

* Checked all fuses - all good. Sorry for not mentioning this in original post *

So given that the screen doesn't glow, looks like the Y-main. And given that I am struggling to remember if the green light was on the input board or the Y-main, it seems likely that it was on the Y-main and therefore the Y-main is faulty?

Thanks again.

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

If you can check the light then that will definitely indicate a bad Y-main. Also check the buffer boards very carefully for burn marks on the chips -- they can fail.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Thanks Tom, will do tomorrow. Will get back to you :-)

[Hedis]

Re: Samsung PS50Q91HD sound but no picture.

I am also trying to repair a PS50Q91HD and I also have the green LED shining on the Y-sustain board.
How should it react with a okay Y-sustain board but unplugged Y-buffer boards? Should it be on or off?

[Hedis]

Re: Samsung PS50Q91HD sound but no picture.

My white power-led on the front of the TV is also blinking 6 times.

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

Lit up LED = Y-main in protection mode.

You can try using these PHILIPS Samsung plasmas guides for some diagnosis of the panel module including the Y-main and buffers.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Hi Tom, sorry I did not get back to you today, had a hectic day at work. I will check the TV tomorrow if all goes according to plan, and get back to you. Thanks for your advice.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

OK, the green light is on the Y-main is illuminated, so it's the Y-main. Tried individually isolating the buffers, no change. I'm guessing a buffer has failed, causing the main to fail, and that I'm just going to have to replace all three. Which means this set is BER.

Thanks for the help with identifying the problem!

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

The Y-main and Y-buffer are repairable, both through repair services online or by yourself if you have the right tools. But if you do decide to get rid of it, please don't throw it out. List it on a free ads site so someone can fix it and save it from being trashed.

[Hedis]

Re: Samsung PS50Q91HD sound but no picture.

Thank you Tom!
I have good electronics knowledge, but never worked on plasma displays earlier. (working as a electronic engineer)

Should the Y-main board have the LED off if everything is fine even with the Y-buffers unplugged?
Most of the buffers on the Y-buffer has shorted out, waiting for new 3407F chips. But want to make sure the Y-main is okay before I blow up the new buffer IC´s.

Any good tips of things to measure to make sure the Y-main is okay? (I have replaced one bad cap (C5709) and one of the FET's (Q5306).
All other FET's measure okay.

(Should I start a new thread instead of hijacking rowage's thread?)

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

Post a picture of your Y-main?
The LED indicates (I believe, but am not certain) one of the -Vsc or Vset voltages is bad.
Usually the top buffer IC blows. At the same time parts on the Y-main fail such as the 88N30W FETs.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Tom, can you recommend any board repairers in Australia? Can't seem to find any. Thanks.

[tom66]

Re: Samsung PS50Q91HD sound but no picture.

Coppell TV repair but they're in the USA. Don't know if postage makes it too pricey.

[rowage]

Re: Samsung PS50Q91HD sound but no picture.

Many thanks mate

[Hedis]

Re: Samsung PS50Q91HD sound but no picture.

I'll continue my repair HERE.
Sorry for hijacking your thread.