Samsung 50" Plasma HPT5044 No Picture

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I've set VA, VS and Ve to the values on the panel sticker. However when I plug the ribbon from the Control board into the XMain Ve goes up to almost 125v instead of the 91v I've set it at and I'm damn sure the same is happening with YMain and throwing it into protection.

Is it expected behaviour for the Control board to this ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

The control board on these sets cannot affect the Ve voltage. High Ve (20% or more) will cause mal-discharge (sparkling positive pixels) Excessively high Ve will drive the panel to full-white causing a PSU shutdown.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

That is exactly the symptom I'm seeing (control board signal causing 37% increase in Ve). I'm left with a few scenarios then one of which is PO swapped out a board for the wrong one. Will remove the XMain and have a look at it.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Removing the five panel ribbons from the XMain and leaving the control board ribbon plugged in Ve remains steady at 91v. Plugging back any of the panel ribbons causes the voltage to rise considerably. Is that normal or ... ? This is without YMain or Ybuffers installed.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

...bump...

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Could a cracked or defective panel make Ve increase on control signals from the logic board ?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Hey tom I stumbled on an interesting read at coppel tv in regards to ymain failures of the samsung models discussed in this thread. According to him the second most common cause is failure/problem of the logic/control board.

http://www.coppelltvrepair.com/p/439...n-board-repair

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I have a new theory

Previously I thought the control board was to blame for the excessive voltage readings I was seeing on the x and y main because it was common to both. There is a simpler explanation I think. Seems like the psu has lost the ability to regulate Vs output and the voltage is climbing as the current demand increases.

Is there a way to confirm that diagnosis before finding the actual fault ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Maybe see my post on my LG 50PS3000. I had a bad Vzbias regulator FET (Vzbias equivalent to Ve in functionality.) My Ve should have been 97V. But it started at 130V and kept creeping up until it hit about 150V, causing the picture to be extremely overdiffused.
https://www.badcaps.net/forum/showth...530&highlight=

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Ya I remember reading that thread. However my Vs is increasing to levels that might be harmful to the panel if I had the buffers plugged in. I only see this when the logic control board ribbon is plugged on. Also I'm having overvoltage problems on the ysus as well. Could be two distinct failures of course. Your understanding is much deeper of course so your input is appreciated.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

I thought your Ve was increasing...? Not Vs?
Extremely high Ve for a long time might cause panel cracking, but it would have to run for many minutes...

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Vs AND Ve. Vs by 10-15v and Ve much higher. When the ysus is connected it goes into protection on its own without buffers connected. No shorts on either board OR the buffers for that matter. Check out that screenshot above with the "DVD" in it - is that what high Vs looks like or maybe just a bad scan ic ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

That's just loose ribbons, or bad soldering.
I'd check your multimeter battery, odd for both to increase....

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Will do some more checking tonight.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

First two pics are Vs and Va on the ps with no x or y mains connected. Bang on at 207v and 63v.

Second two are of Vs and Ve on the xmain with control ribbon unplugged.

Next two are Vs and Ve on xmain with control ribbon plugged in. I forgot the Control board was in test mode.

Last two are of Vs and Ve on xmain with Control board in regular mode.

Both voltages climbed beyond what is pictured before I shut it off.

Wtf is going on ?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Bump

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Yeah, you got me.
Does it still rise with X-main and Y-main out?
Does it still rise on a dark input, such as "No Signal"?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I've only been testing with ymain out. Voltage only rises with control board ribbon plugged to xmain (or ymain before I took it out).

There is a small repair kit available for these boards which fixes known VA and VS tract problems. I didn't think it applied to my situation but then I read this... so maybe ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

I've only been testing with ymain out. Voltage only rises with control board ribbon plugged to xmain (or ymain before I took it out).

There is a small repair kit available for these boards which fixes known VA and VS tract problems. I didn't think it applied to my situation but then I read this... so maybe ?

That is for the cold joints problem which causes Vs/Va to bounce up and down... but not slowly rise.
Does the problem occur quicker if the PSU is heated?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I'm definitely all over the place with this one.

I had another look at the two YSUS boards I have and found one board to have Drain-Source shorts registering on the four fets under the lower heatsink. The other one didn't have any shorts I could find.

So I installed the good YSUS with an upper buffer (no shorts) and disconnected the xmain and when I fired it up I got a picture on the upper half of the screen. Not the best picture but a picture.

The lower buffer board has no shorts but when installed it throws the protection led on the YSUS so I shut it down immediately. Still no shorts on the lower Ybuffer so not sure why it's doing that but that can wait for the moment.

In summary, tom, I think you may have be right about the xmain. The fets are not shorted. How would I go about checking the Vzbias (Ve) circuit ?