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Samsung PS50B530 picture turning on and off

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ProDave:
Sasung PS50B530S2w

At start up, the picture comes on, then goes off (sound remains off)

It then cycles a few times like this. Screen comes on black baxkground (whole screen very slightly illuminated) picture comes on, screen goes  completely black.

Each time the picture stays on a little longer before it trips off, and after a few minutes it stays on.

I have not yet done any diagnostics, I thought I would ask here first if it's a common fault.

A bit more info.

If I select an AV input that has no source, the screen will come on and say "no signal" in the middle.  As soon as I turn on the AV source, the picture will come on then trip as above.

could it be a psu issue? Toom mich brightness on the screen somthing trips? over current? but is okay displaying a small low prightness "no signal" message?

ProDave:
A bit more information. I have the set on soak test and done some measurements.

It's an intermittent fault, they are always the worst.

The picture started going on and off again, All PSU voltages are okay. I did find Ve was a bit low at 84V where it should have been 92, so I adjusted that, but it made no difference.

On the control board, in the middle of the chassis there are two LED's.  The one in the middle near the large IC normally flashes at 1Hz and the other one near the edge of the board is normally not illuminated.

When the picture goes off, the one near the edge of the board gives one short and one long flash, and the one in the middle stops it's 1Hz flashing for a second or two.

Can anyone diagnose anything from that?

ProDave:
Latest progress, I have just tried the set and no picture at all, not even trying to come on.

Now Vs and Va are missing, so look slike a PSU fault. I'll fix ther PSU and see if that sorts it out.

Perhaps to start with the voltages were just glitching, now it's failed completely?

downunder:
Hi Dave,

I'd be interested to know if you have any success with this. I currently have the 42 inch version of this model which intermittently shuts off to standby. Has only faulted a couple of times and I wasn't looking when it happened. Makes it kind of difficult to fault find in its current state, because you can turn it back on with no worries and it continues on its merry way.   -   Bruce

ProDave:
I'm continuing to chase cause and effect.

The set is working again most of the time occasionally the picture starts going off then back on.

Having established that Vs and Va go off then come back on, I have been trying to establish if this is a psu fault or something else.

I have been monitoring VSON which is the signal from the control board to the PSU to tell VS to turn on (and VA)

When the set is operating normally, this sits at 3.22V

Whenever the picture goes off, VSON drops to 0V then back to 3.22V then the picture comes back on.

So is this a control board or main board fault?  Or what else could be causeing VSON to momentarilly turn off?

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