Panasonic TNPA5081 rebuilt, poor image

[keats11]

Hi guys,
So I have a 54 inch Panasonic Plasma TV, which came in with 7 blinks (shorted Ysus=TNPA5081). There are several threads on here which I followed, and replaced many shorted components one by one. After a few failed attempts at power on, replaced more components to the point now the TV powers ON. The image however looks washed. I have been talking to tw2005 about this, and he is puzzled at it as well. I can post the details of the repair if anyone is interested, but the image problem is independent of that. Any ideas what this may point to?

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

Did you check voltages: Vsus (about 200V), Vda (55~75V), Ve (100~150V), Vad (-140~180V) and Vscn (120~150V wrt Vad)?

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

I did measure the Vsus earlier and it was about 200V. Vsus and VAD (I believe) are also routed to the Zsus board, which also I measured. It read 200V and 15V . Not sure how to measure the scan and other voltages without an Oscilloscope. I do have one, just wondering if I need isolation transformer etc before hooking up to Vsus. The vad seems low compared to what you are suggesting.. I'll post in here a little later. Thanks for the suggestions.

[tw2005]

Re: Panasonic TNPA5081 rebuilt, poor image

I did measure the Vsus earlier and it was about 200V. Vsus and VAD (I believe) are also routed to the Zsus board, which also I measured. It read 200V and 15V . Not sure how to measure the scan and other voltages without an Oscilloscope. I do have one, just wondering if I need isolation transformer etc before hooking up to Vsus. The vad seems low compared to what you are suggesting.. I'll post in here a little later. Thanks for the suggestions.

If you have a CRO then that may be a path to take. tom is definitely a big fan. When I had an issue with a SS board, he did say to me if you had a CRO it would have been found that way so there's still hope.

I'll have a look and see if i have any data on my TV. TPVSCN and TPVAD pick off points are clearly marked on the SC, R860 and L472 and bvoltages can be measured using a std meter

[tw2005]

Re: Panasonic TNPA5081 rebuilt, poor image

Found this measured off mine a couple of years ago 50" I did not know waht to do these in respect to as they don't give these anymore in the manual nor are there panel stickers with data either.

VAD to chassis gnd -199V.
VAD to VFgnd -70V

TPVSCN to chassis -53V
TPVSCN to VAD 147V

VSUS 203.8V
TPVe 134.9V

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Took measurements:
Vsus=206
15V line=15V
VAD=-206
VSCAN=-50 (wrt gnd)= -50--206=146 wrt VAD
VDA=61
Ve=130

So the VAD=-206 seems rather large negative compared to your numbers, Tom. But looks right compared to tw2005's value of -199.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Hey if you guys have any info on viewing waveforms on the SC board please tell me. Like I said I do have a 60 Mhz oscilloscope and a probe (may be 10x I am not sure). The main thing I want to know (can't think right now) is if I need an isolation transformer to connect the scope to. I wont need it as long as I am connecting the scope to chasis for ground.. otherwise I'll need it. Going to bed now. More tomorrow.

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

I've never needed an isolating transformer. In theory you'd need it for checking Vscn offset but DC test should be sufficient for that. So I would just connect it straight to chassis ground. Use a 10X probe and ensure that the probe is rated for 400V or more.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Hooked up my oscilloscope.. I see some kind of waveform.. not sure I can get a much better waveform by zooming in .. as I increase the time resolution the waveform goes all over the screen.. having trouble synchronising it. Anyway, let me know what you guys think of this waveform.

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

Do you have a computer you can connect to the TV?
If so connect to it and set the video output to 60 Hz (from the appropriate settings dialog)
Then set your scope trigger to LINE. It's not perfect, but since LINE is at 60 Hz, it'll make it steady enough to get a quick look.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Not sure what you are saying.. I am trying to see if the Ysus is outputting the scan waveform correctly. As I understand it, it does that independent of what I am displaying on the TV itself. What I was talking about is that I cant seem to stabilize the waveform on my scope itself.. which is usually a problem with most things I have tired to look on it. I usually turn the sweep knob to get maximum stability I can. I am not sure how the computer outputting a 60Hz waveform on to the Tv affects the periodicity of the Ysus signal. Padon me if I don't know.. point me to some reading material.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Another thing I could possibly use is the fact that I have another 50 inch Panasonic plasma TV sitting around. The guy told me I think it is TCP50G20? It has the same TNPA5081 Ysustain, but not sure of the suffix. Wondering if I can swap it in here to see if it works? What do you think?

[Alastair E]

Re: Panasonic TNPA5081 rebuilt, poor image

You can use the Ext Sync in on Scope and Trigger on the Video waveform for stability....

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

Not sure what you are saying.. I am trying to see if the Ysus is outputting the scan waveform correctly. As I understand it, it does that independent of what I am displaying on the TV itself. What I was talking about is that I cant seem to stabilize the waveform on my scope itself.. which is usually a problem with most things I have tired to look on it. I usually turn the sweep knob to get maximum stability I can. I am not sure how the computer outputting a 60Hz waveform on to the Tv affects the periodicity of the Ysus signal. Padon me if I don't know.. point me to some reading material.

The way a plasma display works is there are basically 8~12 sub-fields per real video frame. The sub-fields are periods of light emission and are preceded by a reset field (ramp waveform after -Vad period) and terminated by a sustain event - emitting light. For this panel I expect 10 sub fields as it is a 600Hz max sub-field drive panel, this means that each real field will be made of 10 sub fields.

By locking your scope to the 60Hz line signal from the mains electric supply you essentially help stabilise the waveform on the screen if you also have a 60Hz signal. They will not be exactly the same frequency so they will still drift but it may be good enough to get a quick picture. By adjusting SWEEP all you are doing is changing the scope's time-base. Ideally you'd have a way to set the scope's trigger to sync to the waveform (this means it will begin the trace only when a certain signal/pattern is seen) but this is very difficult with analog scopes.

What computer do you have access to. Laptop with HDMI or VGA? Desktop PC. Or perhaps a blu ray player you can hook up a 60Hz program to (e.g. NTSC broadcast TV episodes but NOT movies/cinema.)

Alastair's solution is the best, but it could be hard if you don't have an easy way to get a line/frame sync signal. Such a signal can be derived from an analog TV signal e.g. the yellow composite jack with a BNC to RCA adapter or cable.

Here's an example SC board waveform (actually Y-Main but different name, same function applies) from a Samsung panel:
http://i1190.photobucket.com/albums/...2/ADS00001.png

Notice the increasing width of each sub field. Yours will be a little different.

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

Since this is a common question on the forum I just took these measurements off a Panasonic TH-42PZ8BA showing a full white raster. These should be roughly comparable though I'd expect extra sub fields (mostly short ones) and/or differences in the priming/reset voltages.

1. SC board waveform (FGND / VF node) - primary output. Multiple video fields shown. The VSCN floats on top of this, applied during -Vy excursion by scan/buffer board.
2. Closer look at 1 SF (there are 8 in this panel waveform) which includes a pre- and post-reset field
3. Sustain period (actual light emission)
4. Pre-init period for panel, followed by SF 1 & SF 2
5. SS board waveform, 1 field.
6. One SF of SS board waveform showing reset period (Ve and 2Ve) plus sustain period
7. Closer look at SS sustain waveform

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Alistair, Tom, thanks a bunch for these pointers and fine graphs. I didn't know anything about the subfields.. until today. Let me read through that IR article (gets somewhat esoteric with energy recovery and such) and understand Tom's graphs before attempting to measure anything on my TV. This is great because by the time this is over I would have a deeper understanding of how the PDP works. As for computers, I do have a laptop with vga output and probably DVI/HDMI (my daughter uses it for school work). I also have DVD players that have the yellow composite jack.. I could try to sync the scope using that that (I would need to understand more how to do it). Having fun here!

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

So after understanding a bit more about what the Ysus does, I got a picture of the VFG waveform (the screw terminal). Looks like we have multiple subfields, increasing in width. Still not sure how to do the sync with the signal, once I figure that out, I could try to take a picture showing the whole frame. Does anything looks amiss here?

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

The sus period looks stunted. Normally it would swing from 0-Vsus and back many times per subfield (progressively increasing in width) but your waveform doesn't look to be going beyond 50V.

[keats11]

Re: Panasonic TNPA5081 rebuilt, poor image

Tom, are you saying the "shorter oscillations" (which progressively increase in width) should be the same height as the tallest one? The scope is set at 5V/div and my probe says 10x, so it is really 50V per div. So the tallest spike is above 400V. If that is the case, the shorter one may be about 300V. Are you saying this need to be 400 as well? Making sure this is what you mean by stunted.

[tom66]

Re: Panasonic TNPA5081 rebuilt, poor image

The sus waveform swings around 0V, so you're seeing a wave from 0 to about 50V. Yes it should be about the size of that peak at the end of each field.