Samsung 50" Plasma HPT5044 No Picture

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Ya I have good Va and Vs.

Since this is first time using this scope (any scope) could you point out where to probe the XSUS so I can verify the scopes functionality ? I have the waveforms from the SM posted earlier in the thread.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Can you supply a picture of the X-main?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

D'oh not at home atm, watching sons baseball game

I can dig one up from shopjimmy. Sec...

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

There appears to be several boards, naturally, so will post a pic later on.

Does the waveform, such as it is, imply the scope is adjusted properly ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

The scope should be on 50 or 100V/div and about 2us/div to get a waveform like the one in my pictures.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

So I should push the knob in to rurn off the 5x magnification or does that not factor in ?

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Ok tom, messed around some more. You were right about having a dead ysus. See pic 1 for some insight into what I found when I went back in.

Lol

I think I managed to get a good shot. It seems to match up pretty well with the one in the SM. 2mSec and 50v/div so about +200v to -200v

What you think ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

Done it myself plenty of times! Your Yset ramp looks clipped (beginning of the field), it should peak a little higher; can you try changing V/div on your scope up one notch to make sure it's not an artefact of the scope. Poor Yset won't kill buffers but the image will look poor.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I tried already, can't seem to crunch it down any.

5v x 10x probe = 50v/div, right ? There is a "5x magnification" by pulling the CAL knob out so..

2v x 5x mag x 10x probe = 100v/div ? That should offer plenty of resolution for Yset.

Will try it again later.

Now that I think about it, what actually kills the buffers ? A sustained 200v ?

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

I really don't know what kills the buffers, but I suspect the root cause is related to Vsch being present whilst FG5V is not - however I honestly do not know for sure.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

My scope is rated at 275v. The Yset voltage looks like it could be approaching 300v. Would that clip the Yset spike and explain what I see in my image ?

The bottom of the waveform looks different as well...

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Ok the scope is rated at 250v, not 275v. And the magnification function is just that. So now I need a little help on working the scope.

The highest setting is 5v/div. I ASSUME the x10 probe gives me a max resolution of 50v/div. The grid in the Y axis is 8 high so 400v total. If I try to view the whole waveform (ground at middle of the screen) I clip whatever goes beyond that, Yset being one.

Is it possible to focus on say just the positive side of the waveform such that ground being at the bottom of the display I can view up to a theoretical +400v and thus capture the entire top of the wave ?

[Agent24]

Re: Samsung 50" Plasma HPT5044 No Picture

You could try AC coupling to remove any DC offset, but if the AC component is that high anyway it won't make a difference

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

So this scope is incapable of capturing the ysus output ? Ouch.

[Agent24]

Re: Samsung 50" Plasma HPT5044 No Picture

Maybe you can make your own custom voltage divider and put it in series with the probe? I don't know if that would affect the quality of the signal though.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

Or buy another scope...

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

According to this document..

my voltages at the test points near U5704 are off. My readings are all about 18v and that will KILL the buffers it says. Suspect U5706. Will check it for short not sure how else to verify its functionality.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

The number on your scope is the safe working limit. Your scope should be able to show a full waveform including offsets about 2 x from the maximum 1X input. e.g. at 5V/div, it should be able to read ±40V from centre by moving offset. A 10X will change this to ±400V which is sufficient for capturing VSET, so I suspect you do still have a problem with the Y-main.

[mmartell]

Re: Samsung 50" Plasma HPT5044 No Picture

I'm sorry tom but what is an offset and how do I adjust it ? When looking at my captured waveform it looks like the scope has hit a hard limit at both the top and bottom of the form.

[tom66]

Re: Samsung 50" Plasma HPT5044 No Picture

On your scope, you have a V OFFSET control, or V POS, right? Adjust that.