Samsung 50" plasma blank screen

[Tweek4]

Re: Samsung 50" plasma blank screen

I received a letter from Samsung last week indicating that my tv might qualify for a specific repair under a class action suit proposed settlement brought against Samsung. The suit cites a capacitor failure on the power supply board, I believe and to cut a long story short, the repair guru arrived today and checked the suspect capacitor which turned out to be OK. Installed a new power supply board anyway. He also found a couple of bulging caps on the Y sustain board, did voltage checks, and after close inspection of the display panel found a couple of tiny pots in the lower right corner and declared that the panel is bad. Not worth the expense to fix.
No more plasma tv for me.
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks for the help, Tom66.
I still have a hard time believing that this tv, having very few hours on it and zero problems, failed by just moving it 20 feet.
I'll keep an eye on the forum for ideas.
Thanks again
Peter

[tom66]

Re: Samsung 50" plasma blank screen

yes
Previously I tried a different logic board.

I'm drawing a blank now, I wish I could help. Someone discovered this was a Y-sustain fault on an LG, but they haven't replaced it yet so we can't be sure.

[Tweek4]

Re: Samsung 50" plasma blank screen

yes
Previously I tried a different logic board.

[tom66]

Re: Samsung 50" plasma blank screen

Well- I just received and installed the main board. No change.
Vs and Va voltages are the same as previously measured.
Maybe the SMPS board?

Peter

Which main board - the one with the inputs?

[Tweek4]

Re: Samsung 50" plasma blank screen

Well- I just received and installed the main board. No change.
Vs and Va voltages are the same as previously measured.
Maybe the SMPS board?

Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

I already tried another logic board- no change.
I think I will swap the main board then.
Thanks, tom66
Peter

[tom66]

Re: Samsung 50" plasma blank screen

Further check:
with y and x boards disconnected from the smps, ref Vs=206, Va=56, Vs@x board connector=206, Vs and Va at y board connector=190 and 51.
With x board reconnected, Vs and Va no change.
With both x and y boards reconnected, Vs andVa to y board drop to 186 and 48. Vs to x board no change.
Seems like the smps board is not regulating properly.
Any component checks or replace the smps board?
Peter

I think if the SMPS was not regulating, you would get a dim picture. It might rise under no load, but that is to be expected.

I think you main board or logic board is faulty but can't think of a test to prove it. Someone else on these forums has the same problem with an LG plasma. The only way to really check it would be with a scope.

[Tweek4]

Re: Samsung 50" plasma blank screen

Further check:
with y and x boards disconnected from the smps, ref Vs=206, Va=56, Vs@x board connector=206, Vs and Va at y board connector=190 and 51.
With x board reconnected, Vs and Va no change.
With both x and y boards reconnected, Vs andVa to y board drop to 186 and 48. Vs to x board no change.
Seems like the smps board is not regulating properly.
Any component checks or replace the smps board?
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

I just checked again.
Voltage measured on the smps going to X board: Vs=206v, Va= 56v
Going to Y board: Vs=182, Va=48v
If I unplug Y board connector, Vs=190v, Va = 52v
Still looking
Peter

[tom66]

Re: Samsung 50" plasma blank screen

That is strange - is the voltage disappearing across the board? I don't quite understand the readouts.

[Tweek4]

Re: Samsung 50" plasma blank screen

Tom66...
My tv differs somewhat from the manual I have been referring to.
The power to buffers E and F come through the Y main board on my tv.
Here's what I found.
Va at the test point = 56v. Vs=205v
Va leaving smps board to Y main= 48v(CN810)
Vs leaving smps board to y main= 182v
Va at the Y main socket end was different every time I measured it. From 80v to 240v. Vs at the same socket was 170v. Double and triple checked.
Va to E buffer= 56v.
E to F buffers = 5v, 8v and 8v(3 wire jumper).
Strange Va?????
Peter

[tom66]

Re: Samsung 50" plasma blank screen

Check the vertical drive voltage is present. Should be around 60V and is labelled Va. It may be coming out of PSU but is it arriving on F board?

[Tweek4]

Re: Samsung 50" plasma blank screen

I don't have a scope. Just a DMM and soldering iron.
I'll spend some time on it this weekend.
Peter

[tom66]

Re: Samsung 50" plasma blank screen

Here is a picture of the suspect area of the F buffer, with the aluminum shield removed.
No apparent damage-arcing etc.
Vsc measured -190vdc, normal.
So- I may resolve to remove all the boards in sequence and look for a dry joint.
If this were a hifi project I would be tracing the signal circuits rather than power circuits.
Is it worth checking all the video signal ribbons for continuity?
Peter

Checking for continuity could be useful. If you do hifi do you have a scope? Even a basic 20 MHz one can "see" if the waveforms are there or not.

[Tweek4]

Re: Samsung 50" plasma blank screen

F buffer

[Tweek4]

Re: Samsung 50" plasma blank screen

Here is a picture of the suspect area of the F buffer, with the aluminum shield removed.
No apparent damage-arcing etc.
Vsc measured -190vdc, normal.
So- I may resolve to remove all the boards in sequence and look for a dry joint.
If this were a hifi project I would be tracing the signal circuits rather than power circuits.
Is it worth checking all the video signal ribbons for continuity?
Peter

[Tweek4]

Re: Samsung 50" plasma blank screen

Thanks, Tom66...
There is no damage evident. Just the warped board picture attached to my post # 43.
Since it is the component side that is touching the aluminum shield, I am not sure that is even a problem. I have placed some plasticine type putty ( that yellow semi-sticky stuff) between the board and the shield to separate them. I'll check the Vsc voltage shortly.
Peter

[tom66]

Re: Samsung 50" plasma blank screen

Well, you are correct, the E and F buffers are permanently attached. I removed the aluminum shield to have a close look but I couldn't see any evidence of failure.
One think you may help with - I have been unable to find the test point for the Vsc voltage (-190v). I did find the pot that adjusts the voltage but no pin or solder pad.
There is a resistor adjacent mounted vertically on the Y board that has "vscan" silkscreened next to it.
Peter

You need to measure Vscan across both ends of the resistor.

Show a picture of the damage it MAY be repairable.

[Tweek4]

Re: Samsung 50" plasma blank screen

Well, you are correct, the E and F buffers are permanently attached. I removed the aluminum shield to have a close look but I couldn't see any evidence of failure.
One think you may help with - I have been unable to find the test point for the Vsc voltage (-190v). I did find the pot that adjusts the voltage but no pin or solder pad.
There is a resistor adjacent mounted vertically on the Y board that has "vscan" silkscreened next to it.
Peter