Samsung PS50C91HD - No picture, not sure which board is faulty

[edan]

Hi,
I picked up a 50" Samsung Plasma display panel. I found it at my local recycling drop off, where I have found and successfully replaced caps on a Wharfedale LCD TV. I have no experience with plasma.

The unit powers on into stand-by (I here a few clicking sounds like relays, but no picture. (haven't tested sound). It then resumes stand-by after 15mins.

I would like to replace individual components, but not sure which components/boards to focus on. I understand MOSFETS and CAPS on either Y-sustain, buffer or X-board are commonly faulty. But piecing this information from many fragmented posts in different threads can be time consuming and confusing.

Since I found this TV had already been opened, I'm wondering whether some strange soldering points indicate a previous repair attempt? some components look as if they're missing, or perhaps on the other side. Also the revision date of the x-board seems inconsisten with the other boards. Two of the heat sinks on the Power supply board are cold when operating.

Perhaps, this is irrelevent since I would like to get started on testing components. I would appreciate any help with procedures.

I've attached a photo (dimly lit, but with most boards labelled.) I can supply a better photo tomorrow if necessary.

Thank you!

Here are the specifications:

PS50C91HD
YB(UP)
MODEL NO 50" HD W2A GVE YB(UP)
PCB NO. LJ41-05121A
PBA NO. LJ92-01491A
REV R 1.0 07/04/05

YB(LOW)
MODEL NO 50" HD W2A GVE YB(LOW)
REV R 1.0 07/04/05
PCB NO. LJ41-05122A
PBA NO. LJ92-01492A

Y-MAIN (2L)
MODEL NO 50" HD W2 PLUS Y-MAIN (2L)
PCB NO. LJ-41-05120A
PBA NO. LJ92-01490A/B/C/D
REV R 1.3 07/06/04

POWER SUPPLY BOARD
MODEL NO W2A 50 BN44-00162A
REV 1.0

X-MAIN
MODEL NO 50" HD W2 PLUS X-MAIN (2L)
PCB NO. JL41-05118A
PBA NO. LJ92-01489A/B/C/D
REV R 1.3 07/06/19

DRIVER BOARD (?)
MODEL NO BN41-00888C
2007 06 07

BUFFER (F)
MODEL NO 50HD W2A PULS LOGIC BUFFER_F
PCB NO. LF41-04222A
PBA NO. JL92-01404A
REV NO. R1.6 07/06/12

BUFFER - UNKNOWN?
PBA NO. LJ-9201403A

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

That photo is fine for now - much more welcome than no photo at all!

A few checks to perform:

- Do you have sound with an external source?

- 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.

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

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

It is normal to sometimes see components like that missing. They are added for some versions and not others. If someone removed those components it would look a lot messier.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Hi tom66 thanks for such a quick reply

Plugged in RF cable, no sound. But not sure if menu, etc. is configured for TV Aerial input. There is no glow at all. Checked all fuses, all good. No buzzing sound from anywhere. Hmm.. what are the next steps?

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Hi tom66 thanks for such a quick reply

Plugged in RF cable, no sound. But not sure if menu, etc. is configured for TV Aerial input. There is no glow at all. Checked all fuses, all good. No buzzing sound from anywhere. Hmm.. what are the next steps?

Try connecting a DVD player or other composite source to the input with sound. Make sure to connect video cable too - most Samsung TVs don't output sound without a video source. Then use the "Input" button to switch between sources until you hear sound... which may or may not happen.

Does the TV make a chime when you turn it on? Some Samsung TVs do this.

Also, can you post a picture of the connector coming from the power supply and going to each board? It's going to be the thick 5+ way cable.

[uberplasma]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

go oldschool, start checking voltages
The components may not be missing, just not needed/used on this model
I just did one with wonky voltages, like .8, 1.7 etc, turned out to be rectifier for the 5V power , and a smd fuse, not to far from where the AC enters the board

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

tom66, I have sound working now through the AV in. I've posted a picture of the thick cable connectors.

uberplasma, could you advise on the procedures for checking voltages?

Thanks!..

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Ugh - CapXon on a Samsung. Great for reliability. At least they don't look bulged yet. As you have sound these are unlikely to be the problem as they power the main board which deals with audio.

I've attached an image. Check the voltage on each of these pins.

You should get around 200V for Vs and 60V for Va. The exact voltage will depend on what the panel sticker says.

Careful! This is very high voltage. Don't touch the multimeter probe tips or the power supply while testing it.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I'm getting:
203 Vs (205 on panel sticker)
62 Va (63 on panel sticker)

Tested all the pins on each connector.
Although my multimeter is really cheap and nasty.

What next?

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I'm getting:
203 Vs (205 on panel sticker)
62 Va (63 on panel sticker)

Tested all the pins on each connector.
Although my multimeter is really cheap and nasty.

What next?

Okay, that seems good.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

No buzzing, unless its really, really, quite. I tested in the dark in complete silence... I have just found an advertisment on Gumtree, with the exact same model TV, with broken panel. Circuit boards should be good to use with mine, right? Which ones should I look at replacing?

I would like the satisfaction of locating and replacing the faulty component, and saving some money in the process... so I'm ready for the next step...

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

No buzzing, unless its really, really, quite. I tested in the dark in complete silence... I have just found an advertisment on Gumtree, with the exact same model TV, with broken panel. Circuit boards should be good to use with mine, right? Which ones should I look at replacing?

I would like the satisfaction of locating and replacing the faulty component, and saving some money in the process... so I'm ready for the next step...

Sorry, I misread your last post where you actually said it wasn't buzzing.

The sustain voltages - were they measured with the boards plugged in?

Can you post a closer picture of the Y-main and X-main boards? Does this TV have two buffers or just one? It looks like two from here but I can't quite tell. (The buffers go from Y-main to the panel itself.)

It could be the logic board - this might have a fuse on it. But it's buried under the main board so tricky to get out. Only check it if everything else seems okay.

Causes of no picture with good voltages: Y-main, X-main, Y-buffers, X-buffers (rare), logic board (rare) and main board (rare.)

It's quite likely the parts are the same for that TV but not guaranteed.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Hi tom
I measured with the boards plugged and unplugged, same results.

Attached are pics of the Y-main and X-main.

I'm not certain, but I think there are two separate buffers, connected together.

I checked under the logic board, there is no fuse there.

How do I go about testing the boards for faulty components? Is this the next step?

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Yep theybuffers definitely look connected in some way.

Try removing the upper buffer - does a picture appear on the lower half?

Then replace the upper buffer and remove the lower buffer - does a picture appear on the upper half?

There might be a 5V power line going to the sustain boards... is there a marking anywhere indicating this?

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I tried unplugging the upper then lower buffer boards, then removing them completely, still no picture on screen.

No indication of 5V power lines to sustain boards.. except for one cable from the power supply board to the PULS_LOGIC BUFFER_F (the board running along the bottom of the unit) But that isn't connected to either of the sustain boards.

Maybe I've missed a SMD fuse somewhere? I'm not used to spotting those

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

I tried unplugging the upper then lower buffer boards, then removing them completely, still no picture on screen.

No indication of 5V power lines to sustain boards.. except for one cable from the power supply board to the PULS_LOGIC BUFFER_F (the board running along the bottom of the unit) But that isn't connected to either of the sustain boards.

Maybe I've missed a SMD fuse somewhere? I'm not used to spotting those

Post a picture of the logic board... the fuse is very small.

There is the possibility the panel itself is cracked and you would not be able to tell this without checking the right signals are going the panel module... this requires an oscilloscope unfortunately. Samsung thin plasma TV panels are quite prone to cracking on the edges allowing the low pressure gas to escape and the only symptom is no picture :/.

[uberplasma]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

check all the voltages that are marked on connectors, the problem doesn't seem too far from where the AC is rectified. get the manual here:
http://elektrotanya.com/samsung_ps50.../download.html

no virus found and it is what it says it is
it will show where to look for different voltages, and can narrow it down(backwards) from there. look for a third rectifier in the initial section(hot) section that is smaller than the 2 big twin ones on the heat sink
Use an isolation transformer if possible, or be very very careful, you can get zapped real bad from the voltages on this board

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

check all the voltages that are marked on connectors, the problem doesn't seem too far from where the AC is rectified. get the manual here:
http://elektrotanya.com/samsung_ps50.../download.html

no virus found and it is what it says it is
it will show where to look for different voltages, and can narrow it down(backwards) from there. look for a third rectifier in the initial section(hot) section that is smaller than the 2 big twin ones on the heat sink
Use an isolation transformer if possible, or be very very careful, you can get zapped real bad from the voltages on this board

The OP is getting the right sustain and horizontal drive voltages (Vs and Va.) The problem doesn't seem to be with the power supply.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Ok, here is a pic of the logic board. Hopefuly the panel itself is ok.

thanks for the link uberplasma, but neither firefox nor ie can start the download. May be due to one of my firefox addons. tried disabling anti-virus, etc. If you're able to download it, could you pls provide a link? Thanks.

[tom66]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Sorry - miscommunication. Under the main logic board there's usually a smaller logic board which connects to the Y- and X-main boards. It also controls the X-buffers. It will usually be physically mounted under that metal box for the main board.

[edan]

Re: Samsung PS50C91HD - No picture, not sure which board is faulty

Ah ok. I found that tiny SMD fuse. I just tested it on the board and there is continuity. very low ohms. Do I have to desolder it to check properly?