Samsung PS43D450 Plasma - Very strange VS and VA?

[overlord]

Hey all First post so here we go...

Mananged to get my hand on this TV... has a minor crack on the front but i dont think its deep enough to have broken the panel... hopefully!

The main issue is - there is no picture. Off the person I got it off (on ebay) it apparently had sound but no picture

But in my testing i have had no sound or picture - the red led does come on however...

When I plug power into the back there is a click, and an led flashes on the smaller LVDS board, then there is about half a second of buzz from the X-sustain... a couple of white-noise like flickers on the panel... then nothing?

When measuring the Vs and Va - Vs=~200, Va=~80 - but they RAPIDLY decline to 10V for Vs... and Va = ~0.2 - which im very convinced is either a fault of part of the story.

Off memory, will check later, Vscan was around 120v or something high, and the pins to the mainboard were at their measured levels (15v, 12v, etc)

I can't see any bulging caps on the psu - but due to the fact the voltage declines that quickly even with both sustains disconnected - im going to go ahead and replace most of them.

Any further advice on to what to do next etc would be a great help

p.s. a quick search of these forums found this:

https://www.badcaps.net/forum/showthread.php?t=21793

VERY similar issue, very similar psu in fact - looks almost identical - though there was never any resoultion to that one....


Thanks everyone

Note also, even though im down here in Australia - the sticker on the inside of the TV says "NTSC/PAL" - not sure if there are any major differences between NTSCs and PALs of these on the inside but anyway - i usually play with computers, this is a new area for me!

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Never figured out what NTSC/PAL means in regards to Samsung plasmas, as they all seem to be ticked NTSC/PAL even on US models.

Check the control signal VS-ON from the control board to PSU. If it drops out, the control board is shutting down for some reason. Since you are getting flickers from the plasma panel, it's -probably- not the panel at fault.

[Mt.Man]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Hey all First post so here we go...

Mananged to get my hand on this TV... has a minor crack on the front but i dont think its deep enough to have broken the panel... hopefully!

The main issue is - there is no picture. Off the person I got it off (on ebay) it apparently had sound but no picture

But in my testing i have had no sound or picture - the red led does come on however...

When I plug power into the back there is a click, and an led flashes on the smaller LVDS board, then there is about half a second of buzz from the X-sustain... a couple of white-noise like flickers on the panel... then nothing?

When measuring the Vs and Va - Vs=~200, Va=~80 - but they RAPIDLY decline to 10V for Vs... and Va = ~0.2 - which im very convinced is either a fault of part of the story.

Off memory, will check later, Vscan was around 120v or something high, and the pins to the mainboard were at their measured levels (15v, 12v, etc)

I can't see any bulging caps on the psu - but due to the fact the voltage declines that quickly even with both sustains disconnected - im going to go ahead and replace most of them.

Any further advice on to what to do next etc would be a great help

p.s. a quick search of these forums found this:

https://www.badcaps.net/forum/showthread.php?t=21793

VERY similar issue, very similar psu in fact - looks almost identical - though there was never any resoultion to that one....


Thanks everyone

Note also, even though im down here in Australia - the sticker on the inside of the TV says "NTSC/PAL" - not sure if there are any major differences between NTSCs and PALs of these on the inside but anyway - i usually play with computers, this is a new area for me!

If there is a crack in the glass, that is the panel. There is not a filter glass in front of the panel on this model. If air gets into the panel, many times you can hear the panel buzz or chatter.

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

The buzzing from a cracked screen plasma is (I believe) from the Y and Z-sustain seeing a shorted load due to shorted electrodes - I'm not sure but I don't think the panel itself can buzz. The plasma screen will not flicker at all if it is genuinely cracked.

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Check the control signal VS-ON from the control board to PSU. If it drops out, the control board is shutting down for some reason. Since you are getting flickers from the plasma panel, it's -probably- not the panel at fault.

I can find the control "PS-ON" - and its barely a tenth of a volt when the unit is on - however, the +5v line is around 5.2v, it seems to be the lack of Vs and Va shuts everything down...

Also, the heatsink on the control board (the small one just above the I/Os) does get warm to the touch after running - whereas neither the x-sus nor the y-sus get warm...

edit: i remember reading somewhere that low Vs = dim picture... could an extremely low Vs = no picture? :P

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Yes, no/low Vs = no picture. With Vs of say 200V, picture will be good; if it is around 170V it will be there, dim, but half the pixels will intermittently not fire so you will get a speckled picture. The lower you go the less pixels fire until you get no picture, this appears to happen around 80 - 130V DC at least according to the current drawn by a Y-sus board dropping to nearly zero (I measured this on a 50" NEC.)

I have never been able to test Va failures (they are very rare compared to Vs), however, I suspect the behaviour would be similar (poor/no picture) except the screen would still appear somewhat lit from the priming circuit.

Is there no pin marked VS-ON at all? PS-ON is good as you have good supply voltages.

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Is there no pin marked VS-ON at all? PS-ON is good as you have good supply voltages.

Another quick look and i did find it, PS-ON is still low, say 0.2v and VS-ON seems to be ~0... this is on the power cable connecting the psu to the smaller board (i think its the T-Con board? still learning this stuff :P ) - that board does have an LED light up on it though...

Thank you so much for the ongoing help so far mate

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

VS-ON doesn't vary when it shuts down?

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

VS-ON doesn't vary when it shuts down?

As in when i shut it down or? The unit turns on but does not turn itself off...

edit: got my brother to turn the power off while watching vs_on - went from 0.04mV to 0.00mV...

ninja edit: turning back on again, watching vs_on - it gets to around 3v in sync with the buzz from xsus - then goes to 0 & the buzzing stops

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Ah, so the control board (smaller sub main board with no inputs on it) is for some reason shutting down Vs-ON. I have seen other users on this forum with the same problem. Never figured out what causes the control board to shut down, but usually replacing it sorts it. Do you want to try diagnosing it? If so, post some pictures of it.

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Ah, so the control board (smaller sub main board with no inputs on it) is for some reason shutting down Vs-ON. I have seen other users on this forum with the same problem. Never figured out what causes the control board to shut down, but usually replacing it sorts it. Do you want to try diagnosing it? If so, post some pictures of it.

I'd be more than happy to - looking on ebay controller boards arnt that expensive but it'll be great to find out whats happening to this thing....

i'll edit with some pictures in a sec

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

OK, can you highlight the wire and pin that's connected to VS-ON on that board?

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

OK, can you highlight the wire and pin that's connected to VS-ON on that board?

Left-most pin on the top left of the board

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

OK, it doesn't look like it goes too far... Hard to see (multi layer board) but it might be related to that transistor, and it can make the line high or low; to make it high the transistor turns off, to make it low the transistor turns on. If the on board power supply is not working, then the same thing could happen... Check the voltages at the red and green points I've highlighted.

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

OK, it doesn't look like it goes too far... Hard to see (multi layer board) but it might be related to that transistor, and it can make the line high or low; to make it high the transistor turns off, to make it low the transistor turns on. If the on board power supply is not working, then the same thing could happen... Check the voltages at the red and green points I've highlighted.

Green = ~5v
Red = ~1.2v

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

So, I wonder where the 3V comes from? Is there a part # on the board? (Such as BN44-xxxxxx) Maybe able to get schematic for it.

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

So, I wonder where the 3V comes from? Is there a part # on the board? (Such as BN44-xxxxxx) Maybe able to get schematic for it.

I can see "PCB NO: LJ41-09475A REV NO: R1.6"

i cant see anything with BN44-xxx, the psu is of this form however

I have also removed the board from the panel & can get a picture of the traces on the back if that will help

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Let's see the back, are there any components on there?

[overlord]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

here you go

[tom66]

Re: Samsung PS43D450 Plasma - Very strange VS and VA?

Heh, I was hoping for some voltage regulators... but nope. I don't know what could cause it, sorry...